Author Topic: T-Rex electric build thread (Read 26108 times)

bob branch · « **on:** October 03, 2009, 04:52:30 PM »

I have started a Brodak T-Rex electric arc. I thought, if I can figure out how to download the pictures that I'd share the experience here.

My power system will be as follows: Axi 2826/12 motor. Castle Creations ice 50 esc. Will Hubin 6a timer. Turnigy lightmax 3000 mah lipo. I am setting it up to test two flavors, 4S and 5S. My electric development has been primarily with Rick Sawicki and Frank Carlisle. I bought franks Original 3S axi 2826/10 smoothie from him that Rick helped him set up. This was a clone of what Rick was flying about 4 or 5 years ago. Flying and developing with Rick and Frank genesis went to 4S 4000 mah packs then to Axi 2826/12 motor. Then to Will Hubin timers and 3000 mah 4S power. Props have progressed from woods to APC-E and now APC-E pushers. Frank is not currently flying electric but takes part in a lot of Rick's and my test and tuning sessions. Rick and I have alot of experience with the power system thru the castle creations phoenix 45 but I have switched to the ICE 50 for the data charting feature. I'll probably be changing this esc out with a phoenix 45 as well since I start flying an electric strega on Wen and while I'll start with a pheonix 45 there it will get the ice 50 on occasion as well. We fly the axi 2826/12 planes on 63 ft eye to eye lines usually in the 83 to 8500 rpm ballpark to get 5.3 sec laps with the APC 12X6's. Power has always been outstanding and the /12 motor draws less than 2000 mah per pattern. We have also tested the motor on a 650 sq in 62 ounce plane on the same power and prop system and it flies the plane with authority so motor size is not an issue and we have 3 years of very accurate test data with the system (this year with Will's excellent timers) so we have a plug and play setup that we do not worry about.

Initial weigh in shows the airplane with all components in the bones is 33 oz. The arf covers out in 3.6 oz of ultracote and that is what I will be covering with. The motor with mounts, prop, connectors etc is 9.8 oz with the esc and timer included. Battery options are 11.1 oz for the 4S pack and 13.5 oz for the 5S pack. So all up weight is expected to be 57.5 4S and 59.9 oz 5s. Obviously the 5S will require a different prop combination.

bob branch

bob branch · « **Reply #1 on:** October 03, 2009, 04:58:47 PM »

Well, here goes nothing with the pictures. I hope its easier than our AMA district VII forum. This is a pic of me with the fuse. Frank wanted me in it to show the size of the fuselage. If you get the feeling there is a lot of room up front you are quite right. This is the first electic CL plane (exluding RC conversion) including the strega that I feel I have enough room for whatever I want to do and have multiple options of where to put stuff.

bob branch

Alan Hahn · « **Reply #2 on:** October 03, 2009, 05:00:43 PM »

Keep us informed!

I am not sure if you know how to download the photos or not. In case you don't, all you need to do is to click the "Additional Options" just below the text entry window. Then you will see an "Attach" button that allows you to choose a file. The file size restriction is less onerous than over on SSW, but it probably is a good idea to do a little compression to save Sparky some storage space!

ok you replied when I was typing and clearly know how to download!

bob branch · « **Reply #3 on:** October 03, 2009, 05:18:58 PM »

Fit and finish on the fuse is excellent, btw. This is a whole new level of control line arf constuction. The wood is exceptional. Glue lines are ample. Finally a wood cowl instead of fiberglass. Thank you Paul & John! Now I can finally have a nice film finish on the cowl and not have to paint at all!

This pic shows the front end from the bottom with the cowling off an just after motor mounting. You can see the large fuel tank area. Also note the area that winds up being left behind the motor mount bulkhead. This is a seperate non installed part that you position where ever yo want for your installation. Glow fliers will mount to it as well with RC type mounts. It is absolutely ideal for electric and will adapt to what ever power system you want to use.

The motor mount system I have used I learned from Rick Sawicki. The motor mount bulkhead is located and any motor offset you desire located. A ply strip, in this case 1/8 inch ply is glued to the fuse side in front of the bulkhead location with the bulkhead not in the plane. This is done on both sides. This retains the motor from moving forward. Another similar strip is glued to the fuse side behind the bulkhead. This prevents any rearward motoion. Since most of our stunters have a rail somewhere that is parallel to the thrust line its easy to do this with no incidences. Finally the motor mount bulkhead is slid into place and it is retained simply by two small screws, in this case #2 allen heads that essentially only keep the motor mount from falling out of the airplane. Its simple, light, easy to do, and works. I know doublers are an issue with electrics, to use or not. I use the doubler to act as a stop for these retaining screw heads. It winds up looking leaner than a washer. Thanks Rick, this was my most unfavorite part of electric installations til you showed me this method! I have enlarged the center cutout of the mounting bulkhead to allow more airflow thru the fuse. May not be needed but I am going to be mounting my esc on the front surface of the next rearward bulkhead and want a good air supply going by it.

bob branch · « **Reply #4 on:** October 03, 2009, 05:41:15 PM »

This shows the front end installation a little further down the road. The ice 50 has been installed onto the bulkhead with velcro. Shown is the Turnigy lightmax 5S 3000 mah pack. The fuse is so wide it could be mounted on the outboard side and decrease the amount of tip weight needed. I would do that but since I am going to be moving back and forth from 4S to 5S packs I would wind up with a lateral trim issue so I will mount the batteries on the center line for now. Later when I have settled on the pack I want (and I'm betting it will be the 4S but we will see, that is one of the experiments I am doing on this bird... I always try to do two or three experiments on each new plane to learn more from actual flight testing rather than theory what does what, what works for me and what does not, but always with a distinct hypothesis and planned method of testing each). The timer will be mounted on the inboard fuselage wall in the battery compartment. I use Will's remote start and remote fine tune pot on my timers since I fly with heli hi mode rather than fixed RPM mode. It allows me to adjust the rpm at the circle without a computer, I just dial in the rpm I want. If I want to test a change, I just dial it in and return if I don't get what I want. Same with prop changes. In my hands that's simpler than doing it thru the esc. Your milage may vary. In this thread I'll just be including what has been working for Rick and myself. Btw, Rick usually does not use the remote fine rpm pot, but the one on the board. I just like to be able to change the rpm with the plan on its wheels and running. Once I have what I want I leave it and don't change it. Stays the same every flight just like fixed rpm mode.

I have a problem retaining little screws in my life. Grass seems to eat them and gravity doesn't pull down in my part of the world (maybe because I live on an island) it seems to pull sideways. All little screws seem to have a habit of jumping sideways out of their holes and into the grass. Also I don't like the idea of pulling 4 screws every time I change the battery. Sometimes I use the quater turn latch I learned from Bob McDonald, but I am a little leary of one of those flailing around with all the wires in the front end of an electric fuse. My solution for the T-Rex is magnets. I have place 4 one half inch rare earth magnets (available cheap at Jo Ann Fabrics). Two are in the nose block, and two on the sides of the fuse. I had hoped to get by with only one in the aft section but the cowl didn't sit flat when I did so I had to add the 4th for esthetics. NOT for retention. Good thing the nose is wide open. It takes a small explosion or strong karate chop to open the cowl with half ounce magnets. But the flip side is the cowl will not come off in flight. I retained the mounts for the screws that were in the kit and mounted on the cowl itself as they provide lateral and for and aft limitation for the cowl. This is the ideal situation with magnets. Don't ask them to do both lateral guidance and retention. Lots of cowls and canopies littering the woods and fields around our RC sites from doing this.

bob

bob branch · « **Reply #5 on:** October 03, 2009, 05:55:57 PM »

This is the cowl showing the magnets and their mounts in the cowl. Notice also the glue lines on the stringers. Oh, no blocks on this kit, its all stringer and sheeting and the sheeting is nicely blended, not corners but nicely rounded and blended. Kinda looks like how you might build one yourself doesn't it? The installation of the magnets I learned form my RC building partner Jerry LeLacheur. The mount plates are 1/8 ply. I use a brad point 1/2 inch drill to drill a shallow recess about 1/2 the thickness of the magnet, ie about 1/16 inch deep into the ply. The magnet is sanded to roughen the flat surface and edges that will get glued and it is then glued to the ply with epoxy or thick CA. If using thick CA I wet the bonding surface of the magnet with CA kicker and place the glue in the recess in the ply plate. That causes it to kick and set completely on the inside. One plate is then mounted, I mounted in this case the fuselage plates first. Always check before you glue the magnets by the way that they are facing each other in attraction and not repulsion... they are polorized and only join on one surface. Only each pair has to match. To mount the opposing magnet place a piece of wax paper between the magnets and join them. Apply glue to the ply mount to be mounted (in my case the cowl ones, did one at a time, and join them then seating the cowl. I did it this way cause I had access inside the cowl from the front intake and I had cut out the air duct channel in the bulkhead just in front of the wing. If you look at the first pic of the front fuse area you will see that in the kit this has already been mostly cut through. This allows for the pipe tunnel if you are going that route in glow or for our air exhaust in electric.

I should point out that the magnets wind up being a little proud of the mount plate. That is what you want. On the nose block to orient the opposing magnets, I installed the fuse ones first. Then I painted some black dope on them and seated the cowl down on them. This left a nice black mark on the cowl nose block exactly where the cowl magnets should be placed. I then cut the receiving hole for the magnet deep enough so the magnet would not hold up the cowl fuse joint, put the wax paper between the magnets, and filled the recess with epoxy and set it all together. After the epoxy kicked I separated the parts and trimmed the excess epoxy.

bob

bob branch · « **Reply #6 on:** October 03, 2009, 06:21:28 PM »

Here is a look at the wing. I have assembled it and failed to take pics during assembly. The wing is very similar to the current strega wing. There are two spar boxes in the wing, one in front, one in back which receive lightweight joining spars. These perfectly align the wing halves. They are epoxied in place and the center ribs are epoxied together as well. The manual doesn't mention it that I could find but in that I found a strip of fiberglass tape in the kit and no where else it could be used that I could think of I attached it over the wing joint with thin CA (rather than have the weight of epoxy). Any new arf is going to have some issues on the first go around. This is commonplace in RC and control line. And while this is a much higher step in CL arf/arc construction than anything we have seen before, there are one or two wrinkles to be ironed out. First the pushrods are too small for the pushrod end fittings. I believe I encountered this on my last strega (my fourth btw and first one to get electric power, ... two with Saito .72, one with PA .51 on a pipe (best performer by a very long ways so far). In that I keep carbon fiber pushrod tube on hand that fits the 4-40 end fittings this is no biggie for me. Just made new ones. I missed it in the manual but the tubes are not the correct length in the kit and must be trimmed to the right length. I know it sounds like a no brainer but the RC kits I build alot of that have carbon pushrods all have them precut to the correct length these days. My bad!

A second issue I encountered you can see in the pic. The exit slot for the pushrod is on the wrong wing panel. It needs to be on the inside panel, not the outside. Again, no biggie, just cut a new one. Also, the flap pushrod must be installed before assembling the wing halves. I did this but did not realize that the slot was on the wrong side til I tried to assemble the wing together (with the glue on it of course... good thing I used 30 minute epoxy). The wing will not go together with the pushrod going out the slot on the outboard wing. The alignment spars will not allow it. So I had to remove the pushrod and assemble the wing halves real fast so I didn't get the glue kicking and then later cut a second flap exit slot in the outboard wing. Since I could not get to the bellcrank hole for the pushrod (its a large belcrank, all Tom Morris like control system... ball links, suspended bellcrank... nice job Brad, nice bellcrank reinforcement system too. Be proud of it!) I had to cut a longer slot and again an access in the bottom of the wing to get to the nut to mount the pushrod. Again, no biggie. I may do primarily arf's these days but I spent a lot of years building and it drives me crazy when RC fliers grip about a little mod like this. Be nice in a perfect world if everything was perfect, but first go around it rarely is.

Flaps are built up and covered. Look adequately stiff especially since they are not full span.

Well that is as far as I am for tonight. I'll post further as the process goes along.

Btw, I will apologize now. I am a terrible speller, a terrible typist, and make no apologies for odd grammer. You get how i talk. Besides you all know Midwesterners have an accent don't you?

bob branch
Harsens Island, Michigan.

Dennis Adamisin · « **Reply #7 on:** October 03, 2009, 06:35:08 PM »

Great start Bob! that AXI loooks lost in there, heck you go room for TWO packs!

Harsens Island, that's almost a yoooper isn't it???

bob branch · « **Reply #8 on:** October 03, 2009, 07:49:41 PM »

Dennis

Those Uppers got nothing on us Islanders. Canada is only north and east of them. Here Canada is north, south, east, and west of us! Neat piece of geography!

So what are you saying? 10S?

bob

bob branch · « **Reply #9 on:** October 03, 2009, 08:10:25 PM »

On to cooling issues. There is a very big hole in the nose of this airplane. Air can get in but if it can't get out we are no where. And a small hole ain't gonna do it. We need about twice the area of the hole up front for air exhaust. My solution is going to involve 3 exhaust ports. One on each side of the aft section of the lower cowling, and one in the belly pan. There is an opening in the aft bulkhead of the battery compartment as i already pointed out but its only about 1/3 the size of the intake opening so air flow thru that alone will not pull adequate exhaust flow out. My solution was to cut two openings in the lower cowl one on each side of the centerline stringer and extending up to the first lateral stringer on each side of the cowl. Each is by itself almost the size of the area of the nose intake opening. Add to that the bulkhead exhaust thru an opening in the belly pan larger than the bulkhead opening (just to make sure I get draw) and we have more than twice the intake opening in exhaust opening.

I was concerned though about loosing structural integrity of the cowl when I did this, especially with the strength of the magnets holding the cowl down. Sure enough the first time I removed the cowl it started to crack down the center stringer at the openings. So I placed a vertical keel between the aft and mid bulkhead of the cowl. To reinforce it and help direct air flow so I get exhaust flow thru both the bottom cowl openings and the belly pan opening I placed a divider above the keel that is glued to the keel and the two lateral stringers in the cowl. The structural integrity was recovered and I think airflow will be improved, especially out the belly pan opening. Additionally it resolves the visual impact of a hole completely thru the fuselage from one side to the other. In 100% scale aircraft one of the major issues we encounter is cooling air flow for the air cooled aircraft motors. Full plenum boxes are the norm to direct airflow around and thru the cylinders. Directing the flow the way you want it to go along with adequate exhaust opening are the keys. Many a homebuilt 100% scale aircraft goes thru a long arduous teething process getting this worked out. A little duct work can go a long ways.

Bradley Walker · « **Reply #10 on:** October 04, 2009, 10:20:22 AM »

Quote from: bob branch on October 03, 2009, 05:18:58 PM

Finally a wood cowl instead of fiberglass. Thank you Paul & John! Now I can finally have a nice film finish on the cowl and not have to paint at all!

Heh heh... that would be "thank you Brad". HAHAHAHA!!

The proto #1 had a fiberglass cowl and I hated it. So I specifically asked them to make it out of wood. So they did. I like it much better. they did a wonderful job in fact. It fits like a glove, is lighter, and looks much better cosmetically... and you can cover it will film.

The magnet idea on the idea is one that I missed. I will look at putting it on the next run. I have seen the magnets on many of the other RC ARF cowls and they work great.

Bradley Walker · « **Reply #11 on:** October 04, 2009, 10:31:47 AM »

Quote from: bob branch on October 03, 2009, 06:21:28 PM

(its a large belcrank, all Tom Morris like control system... ball links, suspended bellcrank... nice job Brad, nice bellcrank reinforcement system too. Be proud of it!)

I am... it is one of the major accomplishments of the design.

I wanted a way to join the wing and still make a fully suspended fuselage supported bellcrank system THAT THE USER INSTALLS THE MOUNTS.

Read that last part again. I wanted the builder to glue in in his OWN bellcrank. So, no more bitching when one pulls out. If it pulls out is your own dang fault. The system that I designed not only makes the bellcrank attach the to fuselage sides, it help join the wing itself.

I have all the pictures I sent to the manufacturer. I had to make 3D models!!!

bob branch · « **Reply #12 on:** October 04, 2009, 10:37:42 AM »

Brad

Yea, where did I get "Paul" in that post for cryin out loud!

Was too late last night when I posted it. I should have stopped earlier.

bob branch

Bradley Walker · « **Reply #13 on:** October 04, 2009, 11:37:31 AM »

Bob, you are doing a great job. I am forever your humble servant.

bob branch · « **Reply #14 on:** October 04, 2009, 06:20:21 PM »

Brad

Just hope everyone will be patient with me as I usually only get to build on weekends.

When I get there I'll cover how to do a quality film covering job. With practice (well, ok, its taken me 7 years with guidance from a very good RC coverer, but who ever learned to do a quality paint result in one airlane?) you can get to the point where you can do a contest level film covering job with curves and shapes. There are some tricks though and when I get there I'll cover some of the things I have learned. Here's a picture of my electric Strega as an example. Everything is film including the lettering.

bob branch

Dennis Adamisin · « **Reply #15 on:** October 04, 2009, 07:16:53 PM »

I used the small 1/8" magnets on a Vector and they were not up to the task. Yours look like the 1/2" size? Gotta be great. NICE job on the airflow management too. Neither the AXI nore the batteries stand much of a chance at heating up.

bob branch · « **Reply #16 on:** October 05, 2009, 05:54:32 AM »

Dennis

Yes they are 1/2 inch magnets and are very up to the job.

bob branch

Allan Perret · « **Reply #17 on:** October 05, 2009, 07:43:09 AM »

What is the weight of the magnets you are using for the cowl ?

What is the total cost of the electric power system you are installing in the T-Rex ?

bob branch · « **Reply #18 on:** October 05, 2009, 07:08:22 PM »

Allan

Magnets are 0.1 oz each, 1/2 inch diameter

Motor: Dualsky XM4260CA..........................$99.99 (dualsky america)
esc: CAstle Creations pheonix 45...................74.99 (Todd's Models)
timer: Hubin 6a w/ 2 remote leads..................30.00 (Will Hubin)
battery: Turnigy lightmax 5S 3000 mah........... 37.79 (hobby city) (I have 3 of each of the batteries with CL stunters. seems all I need)
apc 13X6.5E pusher prop............................... 7.50 (Tower Hobbies)
charger: Turnigy accucell 6 balancing............. 34.99 ( Hobby City)

That's the whole deal. Dennis Adamissin is flying his with less expensive and smaller motor and it is working fine. I would use a Turnigy but I wanted to try this size motor to see what it is about. Its larger and more expensive than needed, but several of the experiments I am conducting on this model relate to larger motors in heavy airplanes and how they act in comparison to smaller motors on governor mode. Dennis and I will be comparing data very closely on this. I have an ice 50 esc that I will take some data with as well for comparison and may go to that esc in the end. But this is where I am now.

bob branch

bob branch · « **Reply #19 on:** October 05, 2009, 07:28:51 PM »

Allan

Excuse me I gave you the data on the strega electric in the previous post. Sorry.

The T-rex system is as follows:

motor axi 2826/12 $109.99 (Lobby Hobby)
axi radial mount 17.00 (lobby hobby)
ice 50 esc 80.99 (Todd's Models)
turnigy lightmax 4S 3000mah battery 31.55 (Hobby City) (Again I have 3 of these)
turnigy accucell 6 balancing charger 34.99 (hobby city)
APC 12X6E pusher prop 3.39 (apc)

Also as an alternative one of turnigy motors of similar kv and weight class would provide motor for under $40.

As you can probably see from following the forum there are lots of ways to skin the cat. I look to keep my battery costs manageable after starting in electric with at the time very expensive polyquest batteries none of the 4 of which laster 20 flights in the cl environmnet. My turnigeys have been going multiple years with no issues. Good news is when the plolyquests were not longer adequate for cl they still made great sport flying cells for my electric rc airplanes. Also until I recently purchased teh turnigy chager I have been using cellpro's 4C charger, also a very nice unit but limited to 4 cell packs.

bob

Bradley Walker · « **Reply #20 on:** October 06, 2009, 10:32:38 AM »

That's it?

How long will that rig run (pattern time).

Is there such a thing as a remote shutoff?

bob branch · « **Reply #21 on:** October 06, 2009, 11:05:26 AM »

Brad

I can fly the entire pattern with a 5min 32 sec run that starts the prop when I reach the handle (32 sec delay after hitting the start button... so I use no energy while I saunter to the handle). This gives me 6 to 10 laps after the pattern before engine stops ... the timer does this.

but that is not the good news! The good news is you don't need to fly an entire pattern. I set the timer for its minimum run during all trim flights. About 2 minutes. That way I can do the trim flight. Evaluate the changes on several maneuvers, land, make any additional changes, and fly another trim flight without changing or charging batteries. I can easily get two flights from the 3000 mah packs. Used to easily get 3 from the 37-4000 mah packs but prefer now not to carry the weight. Could easily get two trim flights from a 2600 mah class pack as well. Its amazing how much more trimming you can do in a day not having to fly entire pattern for each flight. You really can get a plane dialed in alot faster electric than glow because of this.

bob branch

Allan Perret · « **Reply #22 on:** October 07, 2009, 02:36:59 PM »

Quote from: bob branch on October 05, 2009, 07:28:51 PM

The T-rex system is as follows:
motor axi 2826/12 $109.99 (Lobby Hobby)
axi radial mount 17.00 (lobby hobby)
ice 50 esc 80.99 (Todd's Models)
turnigy lightmax 4S 3000mah battery 31.55 (Hobby City) (Again I have 3 of these)
turnigy accucell 6 balancing charger 34.99 (hobby city)
APC 12X6E pusher prop 3.39 (apc)

No timer ??

bob branch · « **Reply #23 on:** October 07, 2009, 05:06:13 PM »

Alan sorry, the timer is the Hubin 6a with 2 remote leads, start button and fine tune rpm pot.

The T-rex system is as follows:
motor axi 2826/12 $109.99 (Lobby Hobby)
axi radial mount 17.00 (lobby hobby)
ice 50 esc 80.99 (Todd's Models)
turnigy lightmax 4S 3000mah battery 31.55 (Hobby City) (Again I have 3 of these)
turnigy accucell 6 balancing charger 34.99 (hobby city)
APC 12X6E pusher prop 3.39 (apc)
hubin 6a timer w/ 2 leads 30.00 (Will Hubin)

bob branch

Dennis Adamisin · « **Reply #24 on:** October 07, 2009, 05:07:29 PM »

Bob laments his typing lapses, and looks like you caught him in the act. The Hubin timer is listeed in one of his equipment posts but not the other, he WILL be using it tho!

bob branch · « **Reply #25 on:** October 07, 2009, 06:51:01 PM »

Dennis

I hate it when someone beats me to a pun. Good job! Everyone else: I apologize

In these photos I am showing the install of the Will Hubin 6a timer. This version of the timer has the following features: Adjustable flight time from 2 to 6.5 minutes. Adjustable start delay from 0 to 32 seconds. switch to set either governor mode or fixed rpm mode. Two speed adjustment pots. Gross adjustment pot on the board for setting governor high or low and ballpark rpm setting, and fine tune pot on a remote for fine rpm adjustment with about a 1500 rpm range. Provision for retracts. Ability to select multiple rpm settings for flight. I fly in governor mode vs fixed rpm mode so the mode switch on the board is in that position and I set the final rpm with the fine tune pot. Also the second remote is a start button. The first pic shows the setup from the outside of the plane. The red button is the start button. The stem is the fine tune pot. To those of you who fly glow power, think of it as my needle valve. I use it the same way you use yours to adjust rpm. I adjust it to create the rpm that gives me the lap times I want. If its windy and I'm going too fast, I slow it down. If it is dead calm and I need a bit more power I dial it up a bit. But once I set it it does not need to be adjusted again unless I want to change rpm. It will always fly to exactly the same setting throughout the flight. The two 4-40 allen bolts are the mounting bolts for the timer.

The second pic shows the inside of the plane. The start button is the rear most remote, the fine tune pot the closest to the timer board itself. The orange wires are the communication wires from the timer to the speed controller. The blue square devices on the timer board are the adjustment pots and the black switch on the red section is the selector for governor or fixed rpm mode. The 3 bottom connector wires on the board not used are for a retract servo if used. The velcro will be discussed in the next sequence of pics.

bob

bob branch · « **Reply #26 on:** October 07, 2009, 07:07:19 PM »

There are probably as many battery attachment methods as their are electric fliers... probably more. We each have probably tried a bunch. This one is one i have used often in both rc and cl and works well in my hands. It allows me to move the battery forward and aft for cg adjustment, and it allows me to change to different size batteries but use the same mount system with no modifications. In my RC planes I can vary from 2300 3 cell to 4000 mah 5 cell without changing anything, and have in the same plane. But again, its just what works in my hands. Your milage may vary. (Its the first place I try to peak when I see someone else's cl electric.)

First pic the velcro loop material is epoxied to the what would be the tank upper floor if this were a glow model. This is ply in the T-rex and in Strega as well. I think most battery mounts I have seen are ply these days. I also use two #2 X 1/2 inch allen head screws with washer heads (though the washer heads do not show well in this pic) that I get from R&L fasteners. btw, they have excellent fittings at exceptional prices. Good folks.

The second pic shows the battery. I epoxy velcro hooks to the top and bottom surface of the battery. Notice that I have the battery so that it will mount not lowest profile to the mount surface, but highest. This lets the cg of the battery be lower and helps bring the lateral CG closer to that of the glo motor. Just decreases another trim issue that a few have noted with electric since our power systems usually have more localized vertical cg than glow installations.

The third pic shows the battery installed. It is at the rearmost position in the compartment. I have about 3/4 of forward movement without modifying the bulkead at the front of the compartment. If I need to of course I can open that up and move further forward if I need to. The velcro hooks on the side of the battery you do not see (ie against the tank floor) locates the battery from moving for and aft and laterally. The Hooks on the bottom of the battery, the surface you see, retains the pack. Gives good stable battery location with out any more weight than required, even in 3D rc with 4000 mah 4 cell pack and extremely violent 3D snaps.

That's all for tonight. Winds in the 45 to 50 mph range here in the Detroit area prevented my electric strega having its first flights today. Maybe Friday, but we have wind in the forecast then too. We'll see. Sounds like a few of the glow T-Rex arf's are ready to fly. Looking forward to reports.

bob

Mike Scholtes · « **Reply #27 on:** October 08, 2009, 02:01:24 PM »

Hi Bob:

Many thanks for your most informative build documentary. This is very helpful to E-neophytes like me and I have adopted several of your ideas into the China Clipper E-project. It is so much better to have a road map than have to find the way by yourself. I really look forward to the "covering with film" segment when you get to that point.

What holds the motor mount plate in place? It appears to simply slide into the slot between the bracing ply pieces.

bob branch · « **Reply #28 on:** October 08, 2009, 05:49:47 PM »

Mike

The motor mount does indeed slide into place as you envision. There are two #2 allen head wood screws (from R&L Fastenings), one on each side of the fuse going thru the fuse side and into the motor mount plywood. Their only load is to keep the motor mount from falling out the bottom of the plane. That is all that is needed. Because there is a plywood doubler on the inside of the fuse, I did not use the version of the screws with a built in washer (allen head servo screws). I used the version without the built in washer and when I placed it the first time (use a 1/16 inch pilot hole) I just drew the screw head into the balsa fuse exterior until it bottomed out on the plywood. Deal done and the head comes out flush with the fuse side.

I'm glad you have found some things on the thread you can use. Whenever you can get a look inside anyone's planes you can to see the methods they use. Nothing original in any of my work. I'm just copying what I have seen others do and where I can remember the original source I'll certainly give them the credit they deserve. Where I can't remember, just know its copied from someone.

bob branch

Han Slaats · « **Reply #29 on:** October 09, 2009, 09:09:04 AM »

Bob,

I noticed that the picture of the T-rex wing shows far less ribs than the prototype pictures I saw from Bradleys thread. The gaps between the libs look major to mee. Any issues with torsional stiffness of the wing ? How about covering sagging between the ribs ?

Keep up the good work; we are all taking a lot from this thread.

Han Slaats

RickS · « **Reply #30 on:** October 09, 2009, 12:15:27 PM »

Hi Mike, Hi Bob,

Mike, in response to your question 3 up. This is from Rick Sawicki, we chatted earlier in the "45 year old model" thread.

I can offer a little more about the motor mount system and offer an additional use of it. I developed the motor mount system about 4-5 years ago back when electric stunt was in its infancy. At that time we did not have the wealth of data and data sharing that is now so readily on the web today. The system was initially developed to allow a "quick change" of motors in an airplane. Different motors could be pre mounted..including any spacers, washer offsets etc onto their own firewalls. All of which were made to fit in the same location on the plane and anchored by, in my case 4 screws through the body sides (all the planes had plywood doublers added) and in Bobs case 2 screws, same method. This proved invaluable about 4 years ago on an electric Viking OTS when I had 3 different motors all individually mounted on their own firewalls and were taken to the flying field for an all day session (weather was perfect). By the end of the day all 3 motors were tried several times each and one was selected as being superior to the others in this specific airplane. Being able to change a motor is less than 5 minutes sure helped. I have been using it in all my planes since then and so has Bob. I think it is a great, easy to install, and easy to change motor mounting system.

Mike,...you mentioned you were looking forward to Bobs "covering with film segemt"...believe me it will be well worth the read. He truly has done some fantastic work in film covering.

Hi Bob,

You are doing a great write-up with a lot of important detail that I'm sure will help many others in their incorporation of electric power into either a T-Rex or also be very useful in adapting electric power into other planes. I am really looking forward to your sharing with the electric community your methods of film covering since I have seen all of them first hand and can atest to their beauty.

Rick Sawicki

Mike Scholtes · « **Reply #31 on:** October 09, 2009, 02:35:03 PM »

Hi Bob and Rick and anyone else involved:

I do want to try several motors in the China Clipper so this approach to motor mounting is very useful. I plan to use the TGY 42-50 as the primary motor but have that AXI 28-26 on loan and want to pick up a Scorpion 30-26 (probably) to compare. Like Goldilocks, I want to see which of the three is "just right." Incidentally my TGY seems to be put together well, no visible problems. Has 5mm shaft and Japanese bearings. I will say the "notchiness" as you rotate the can is much more pronounced on the AXI than the TGY but don't know if this has any operational implications. The Adamisins (IIRC) are using this TGY with great success, and it sure is a bargain.

Bill Ervin · « **Reply #32 on:** October 09, 2009, 05:11:59 PM »

Bob, I'm enjoying every post of your T-rex electric build, finally understand the motor mount system you're using and that Rick developed. Being able to slide the firewall in and out for quick motor swaps is pure genius! Things like this make this forum a great place!

bob branch · « **Reply #33 on:** October 09, 2009, 07:29:09 PM »

Han

I do not see any torsional rigidity issue at this point. In 3D RC this kind of spacing is pretty much the norm and no problem with film covering, even crapcote which none of us use here (I hope). From quality films like monocote and ultracote certainly no issues at all. I'm not sure about silkspan and polyspan. I have not done silkspan since I was a kid. Polyspan doesn't seem to pose any issues from my experience but maybe someone with more than the 3 or 4 planes I have done in it could confirm that. I am sure someone else will do an arc and paint it. I just don't paint any more and will not accept the weight. (note: not accept the weight is slang for "I've wet sanded for the last time in this life!".... just more in stunt slang. Bless you all who do it so light and so well!).

Bill

I know Rick doesn't want me to say this and no one on this forum wants me to but since there are some glow fliers reading it I thought I would interject, this mount will also work for glow motors easily if you want to trade in and out.... or IF you have the courage to compare your glow powered version tit for tat with an electric powered version. Just slide the motor and tank out, slide the electric system in! Don't look now, but we are going to beat alot of the glo powered planes weights that have already been posted with some electric power sytems in this bird!

bob branch

Douglas Ames · « **Reply #34 on:** October 10, 2009, 12:26:12 PM »

This may sound like a silly question,
but do you think that your multiple cowl magnets might interfere with the operation of the ESC or Timer?

Alan Hahn · « **Reply #35 on:** October 10, 2009, 12:49:55 PM »

Quote from: Douglas Ames on October 10, 2009, 12:26:12 PM

This may sound like a silly question,
but do you think that your multiple cowl magnets might interfere with the operation of the ESC or Timer?

Not a silly question, but no it won't matter. The ESC could careless since a static magnetic field wouldn't affect it in the least. And any effect on the motor also would be slight---maybe a small eddy current in the iron shell. I use them in all my setups.

bob branch · « **Reply #36 on:** October 10, 2009, 05:35:39 PM »

Before I leave the cowl and engine compartment for other components I'm going to jump ahead a tad to a step of the film covering that I will go into later in more detail. But this comes under the area of a minor detail, but one that can make a nice difference in presentation of the finished project and a huge decrease in frustration level. The basic color scheme of this aircraft is going to be similar to the strega pictured above. Black primary color, white secondary and trim in yellow and orange. Maybe a little something else, I have to wait to see how it lays out. But the entire lower half of the fuse is going to be black. Some places are just aweful (read nearly impossible) to cover well. So why kill yourself? Most notably in this plane the area where the cowl joint is at in the nose block that the magnets are mounted in and the air exhausts and ducting. If you notice when I did the air exhaust I added a keel between the two openings to visually eliminate the hole thru the fuselage that would have been visible both on the ground and in the air. Then I added a duct above it to increase stiffening and direct air thru the belly pan as well as out the exhaust ducts. Covering all that intricate small surface would be nuts. (sorry my humble perspective there). Its inside the fuse. Its not part of the outside surface. It doesn't have to be high gloss, or even smooth. Its all in shadows. It just needs to not be seen. In this case it needs to be black. The area were the magnets face on the cowl nose block will be similar, you could look into that area and not see black and its going to be a tough area to cover and the bottom of the nose bowl opening the same. Solution? The traditionalists are going to love this..... dope.

Notice I did not do the entire insides of the plane. You can. But I have found I often need to do additional grinding and glueing later on. Paint just inhibits the bonds. Remember, battery packs will change (as we will find later, already have), timers and esc's may get changed out, indeed motors and mounts may get redesigned and changed. Not having paint in there leaves this a much easier deal. Glow folks obviouisly have to seal some how. Your choice with your favorite. And I know there has been some discussion about protection from glow fuel at circles getting blown into electrics. Again, your choice. But all I want is to get rid of non black visuals on the model when its done. On the inside all I did was the areas that might show. The battery will cover the rest of the opening area of the exhausts when viewed from the bottom looking up so no reason to black there.

Also, I do not want a smooth nor a sealed surface. When I go to cover, I want the surface as porous as possible. I want grain and as we will see later, I'm even going to make the surface so porous you aren't gonna believe it. I'll warn you now, you will think I have lost it when we get there. Suffice it to say now that smooth, non-porous surfaces trap air and make bubbles that are difficult to make go away. I want to avoid having film finish on painted or sealed surfaces whenever possible.

bob branch

bob branch · « **Reply #37 on:** October 10, 2009, 05:49:00 PM »

Now onto the wing for a bit. I'll have to defer to someone who got the wing together correctly. I just missed how to do it right and as no one esle has mentioned it this was obviously an area of brain lock on my part. The flap pushrod exit is indeed on the right side of the wing as it is in the kit. I still no idea how the wing goes together when the pushrod is in, but since others have done it it obviously does. Sorry for the confusion to everyone following this and my apologies to Brad for not being able to figure it out. At any rate, as we all have to do from time to time, I had to improvise to get myself thru it. I had cut an additional opening on the inboard wing section. Didn't want to leave that open and wanted to strengthen the area so I added a bit of sheet balsa on top of the wing. Its going to be in the fuse, so not seen. Just me an one or two of you will know and I know none of you will tell.

I am not using a standard flap horn. I have an adversion to tweaking wires in flaps to get wings to fly level, and I'm not good at it. Many of you are masters at it. I marvel. Frank Carlisle is just scarey good at it. I used to use separately hinged and adjusted tip trim tabs like beyond the flaps on this plane. But Bob McDonald showed me a fitting he makes that I have used for a number of years now. The horn is in two sections with the actual horn arm on one side and a quadrant with a slot on the other half. A locknut is soldered to the side of the horn arm opposite what we see in the pics and there is a slot in the quadrant so that the two sides of the horn can rotate free of each other and be locked by tightening down the bolt. There is also an index of one side of the horn into the other so that there is no flex between the two halves and they stay centered. Sorry, I'm not CAD literate to do a nice cad representation like Brad and some of the rest of you, but I show it here just to show what it looks like and the extent of the travel available. A small hole is placed in the fuse side opposite the head of the bolt for the allen wrench to pass thru to loosen and tighten as needed. Of course once you are trimmed you are done. .... unless you change something, in which case you can reset it any time. No torquing on the horn wires or the flaps themselves. The flaps do not have to be made so strong and heavy where the wire passes because they do not have to be able to handle the loads of tweaking the flap wires. For me its just easier. You milage may differ of course.

The first pic shows the horn locked with the tow sides even. The second shows the range of adjustment available.

bob branch

Crist Rigotti · « **Reply #38 on:** October 10, 2009, 06:06:32 PM »

Bob, how about another picture of the flap horn from the opposite side..please?
Thanks.

bob branch · « **Reply #39 on:** October 10, 2009, 06:33:38 PM »

Christ

Here ya go.

bob

bob branch · « **Reply #40 on:** October 10, 2009, 06:54:18 PM »

You may recall I also made the flap pushrod too long. So tonight I am redoing it. Now that I had the flap horn glued in and connected so I could get the right length. One of the things this let me do was some deconstruction analysis of my end fitting joint to the carbon tube. I have used carbon tubes exclusively since returning to cl and had used them a lot in rc previously. I was really surprised when I read reports of failures by some folks. I spoke with Curt Nixon about it at the time and we compared methods of joining and found we were both doing it the same. I learned this method in bonding sailboat masts and carbon fiber canoe paddles. Its used in other places and I'm sure by many of you, but being able to deconstruct this end fitting shows why the key step works so well.

In assembling the end fitting its important to make it so that it cannot rotate. There is no anti-rotation built into the end fittings other than the bond of the J.B. Weld to the tube. This is normally very good, but there is a way to get extra security to enhance anti-rotation properties and to give a better bond in the process. The key is to provide relief to the J.B Weld inside the tube and to provide exits for the epoxy that key it further to the tube. I do it by drilling several 1/16th inch holes thru the tube at 90 degrees to each other in the area the end fitting will be. When the end fitting is slid into place it the J.B. Weld will flow out these holes, seal them, and create antirotation for the fitting. Also one of the holes must be beyond the end fitting at at least one end of the tube. Otherwise the epoxy will form a seal, compress the air inside, and partially push the end fitting out during the time it takes the material to set... ie a number of hours. When you go to place the J.B. Weld into the tube after it is mixed, angle the tube at about 60 degrees to the mixing pad and scrape the tube into the mixture tube opening first. This will force the material up the tube. You will be able to confirm it cause it will flow out the holes! When it has come out the last hole that the end fitting will pass it is filled. Dab some on the end fitting and slide it to place. Wipe off the excess and then apply heat shrink to the end of the tube and the end fitting. This helps hold the end fitting in place and strengthens the tube against splitting, its weakest direction. Then do the other end. The J.B. Weld fills the hole and restores sturctural integrity to the area the hole was drilled in.

In this pic I have cut off the end of the tube with the end fitting in it. I then used side cutters to crush the tube and pealed it away on one side. You can see the JB Weld clearly around all areas of the end fitting and in the indentations in the end fitting. I removed the J.B. Weld that was beyond the end fitting into the tube, about 1/4 inch of it. Sorry, would have been better had it been there for you to see but I was trying to capture one of the relief holes. If you look very closely at the pic at the tip of the arrow you will see one of the relief-anti-rotation holes with the lighter gray J.B. Weld filling it. As you can see, like the rest of the fitting, its an intimate fit. Hope this helps clarify this type of pushrod and end fitting some. They really do work well and you can do them yourself. Just be sure to give the J.B.Weld a full 24 hours before disturbing it.

bob branch

bob branch · « **Reply #41 on:** October 10, 2009, 08:04:38 PM »

Hmmmmmmmmmmmmm. Now this is disappointing. I went back down to my shop to see what was to do next. Set all the hinges in place to prefit everything.... it did. All of it. Well, I had to increase the depth of an elevator hinge pocket. That was it. There are no cowl holes to cut. The cooling openings are all done. I joined the shortened elevator pushrod end fitting. Now I am at major disappointment. BRAD!!!!!!!!! What have you done to me? The rest of it is perfect! You have left me with no choice but to do my most unfavorite part of the whole thing! I have to start sanding! EUCH!

Its really that well done! So tomorrow I will start the sanding. I'll start at about 150 grit and take it out to 320 and do any filling I need to. Some of the dents will come right out with a few drops of water and the heat iron to swell the wood back up to contour. One or two I may have to add a little filler but not much. After the sanding is done at 320 is when I will return cause one of the most important steps in covering follows before final sanding. It the one that will abhore you.

See ya when the dust settles.

bob branch

bob branch · « **Reply #42 on:** October 16, 2009, 11:33:41 AM »

Oh Yea! I found one more thing to do before I had to start sanding! Here I am constructing the belly pan air exhaust. I did the same thing as with the cowl. Cut the openings, built a keel, and topped it with a floor. In addition as you will see in one pic I closed off the lightening hole at the back the duct area. There is a mid bulkhead in the belly pan that has an opening to i imagine ease pipe installations. Least that's what I would use it for. Anyway, I want the air directed out this opening and so do not want air going aft in the fuse past it. Lastly of course, I got out the dope and turned the area black for the same reasons as before.

EUCH! Now to sanding!

bob branch

bob branch · « **Reply #43 on:** October 16, 2009, 11:36:34 AM »

Guess it would have helped in the last post if I had added the pictures. Sorry, senior moment.

bob branch

bob branch · « **Reply #44 on:** October 16, 2009, 11:38:45 AM »

You might think that is alot of exhaust opening but its not. Each pair of exhausts is 3.5 inches long and the area of each pair is the equivalent of the area of the intake in the nose. Its a big hole up there! So twice the exhaust area as intake area will give good airflow.

bob branch

bob branch · « **Reply #45 on:** October 16, 2009, 01:37:14 PM »

I'm including this next step just cause I learned it this last year. I know many of you know about it but no one told me before and since I hate to sand it saves a lot of sanding and filling and sanding. Its the way to get rid of dents and scratches and such without sanding. The pics are of the top of the horizontal stab. But if you want to know the magnitude of what the method can do, if you have a T-Rex you will probably have already found the dent in the wing tip caused by the packing of it next to the bellcrank nut. I have seen it mentioned by several people so I am sure someone else has seen it. Unfortunately, even I did not think the method would remove it, but it did. If you have the arf and need to get it fixed, it might be worth opening the wing tip covering to do so.

To do this you place a few drops of water on the divot, dent, whatever. Then you apply a hot monocote iron to it. I use 300 degrees on mine so we are not talking low temps but pretty high. You do not want to rub the iron over the surface, but lay it on the surface of the wood and let it steam the defect. You should hear a good hiss and see steam rise if you are hot enough. The iron should be to temp and you should apply it right after applying the water. You are going to steam the wood. If you are on a curved surface, roll the iron over the defect so the iron is able to provide the limit of contour for the raising of the wood. The wood will swell and come right up to the contour of the iron. If you move the iron or run the iron over it you will probably not transfer enough heaat right where you want it and you will probably mar the very soft wood at this point. (No fear, just steam the area you dented.

The pics were taken with a macro lense from about 6 inches away. The two pics were taken about 30 seconds apart.

bob branch

bob branch · « **Reply #46 on:** October 16, 2009, 01:38:36 PM »

I won't say my next thought, but you can probably guess.

bob

Alan Hahn · « **Reply #47 on:** October 16, 2009, 02:22:51 PM »

hmmm, that doesn't sound good!

Bob Reeves · « **Reply #48 on:** October 16, 2009, 02:33:20 PM »

Quote from: bob branch on October 16, 2009, 01:38:36 PM

I won't say my next thought, but you can probably guess.

bob

Nothing left to do but sand....

Dennis Adamisin · « **Reply #49 on:** October 16, 2009, 03:42:15 PM »

Quote from: bob branch on October 16, 2009, 11:38:45 AM

You might think that is alot of exhaust opening but its not. Each pair of exhausts is 3.5 inches long and the area of each pair is the equivalent of the area of the intake in the nose. Its a big hole up there! So twice the exhaust area as intake area will give good airflow.

bob branch

Bob:
Seeing how old Rex was designed for one of those Infernal Combusting engines, the air intake actually may be larger and in the wrong place for your needs - Have you considered baffling? Maybe closing off all but a circle around the AXI, so that all the air tat comes in MUST pass by the motor? That would certainly re-balance you areas too - exits would be comfortably large...

Looking most excellent - now get back to your sanding.

Author Topic: T-Rex electric build thread (Read 26108 times)

Alan Hahn

Alan Hahn

Alan Hahn