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Building Tips and technical articles. => 1/2 A building. => Topic started by: Dennis Adamisin on October 28, 2009, 12:14:24 PM
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Don't know if there is anybody in SH who is better at staying "on message" then our mutual buddy Doc Holiday - who always reminds us to "have fun". I'm in the process of following Doc's orders with this, a decidedly non-competition oriented little time waster - that ought to be a blast!
Those who attended the Brodak Fly-In June '09 got a chance to see ( and some got to fly) the prototype of the new electric powered Baby Clown. Well two prototypes later, the package was finalized, orders placed and complete power systems will be available around the end of November. The new Brodak electric power systems slated for the Electric Baby Clown ARF will be available separately as a set and can be used on most any 1/2A models. Quiet electric power in a 1/2A is the ultimate noise-friendly answer for backyard or park flying and electric twins are WAY easier than IC twins! To prove that, I took on electrifying the Brodak 1/2A Twin Mustang.
Pix 1: The plastic firewall style mount used on many of the Brodak 1/2A’s is pre-drilled with the holes in a rectangular pattern for a Cox reed valve engine. The electric motor mount is an “X” with the mounting holes on a square pattern which does not fit all 4 holes in the plastic mount – but it will fit two holes diagonally - because of this the change out to existing birds built for Cox reedy's should be pretty straight forward. In most cases 2 screws is probably be enough to retain the motor, but it is a cinch to drill the other two holes (3/32” drill) for the other two 2-56 mounting bolts and nuts. The motor mount ends up skewed a few degrees – but that is of no concern and it still covers the mount and the notch for the landing gear wire.
Pix 2: We will be using two motors and two speed controls but only one battery and one timer to control our new thoroughbred. To accomplish this we will add a pseudo “drop tank” to the middle of the wing to mount the battery on. This will make battery access and change-outs a breeze and actually works in our favor by improving the vertical CG.
Pix 3: Two “Y” wiring harnesses are needed: one will connect the battery circuits of the two ESC’s so they can be connected to a single battery, the other will connect the signal harnesses from the ESC's so they can be controlled by a single timer.
Pix 4: A standard RC Y-harness can probably be found for the timer circuits, however one critical change is needed - note the red power wire from ONE side of the harness must be disconnected/disabled.
Pix 5: The two harnesses are installed in the wing center section with the plugs that go to the ESC’s exiting out the leading edge, the common plug for the battery exiting out the wing bottom center – where the battery goes. Finally the wire to the timer will exit next to the inner side of the outboard fuselage. The timer will be installed about midway back on that fuselage to kind of keep it out of sight while still making it accessible. Up front, we will install the ESC’s in the center most sides of the profile fuselages so they do not stand out quite so much.
Pix 6 & 7: The rest of the F-82 build goes pretty much to plan. I will cover all the subassemblies separately – like an ARF – then assemble them. More pix to follow...
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I will say that the Brodak f-82 was a favorite flyer of mine. My son and I just loved this airplane. I had 2 Black Widows on it that just wouldn't run consistently. It would take multiple flights, but I would get them pretty close. The next problem was they wouldn't quit successfully. I think with electric power this problem would be solved. I was able to fly this plane on lines as long as 50'. I stuck with 42' most of the time but it was a surprisingly good flying plane out of the box. It mets its demise one day coming out of the wingover when an engine failed. I bought another kit and haven't assembled it. Ken
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Seen the PM and I jumped over here. That looks like it is going to be fun. Wonder if Clancy's controller would control the speed. Be great to do touch and go's, plus taxi. Again keep having fun, DOC Holliday
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Hmmm, surprised this thread has not garnered more comments - for any of us who have flown IC twins, electric power makes it pretty darned simple.
A few more pix showing the now RTF bird. If you look closely you will see the props are counter-rotating the RH rotating on the right the LH on the left. This was just like the full size F-82. The prototype had the engines the other way around and it would NOT take off due to the downwash on the center panel. The swapped out the engines - putting the RH rotation on the right side - and - problem solved. The F-82 was not in service very long but it established itself as an long range escort fighter (its original intended role), ground attack, night fighter and all-weather interceptor at the time that the USAF was trying to bring the first recalcitrant jets into service.
The model weighs 12 oz, which I THINK is about 1 ounce more than it would have weighted with a pair of Black Widows.
Kenneth: THANKS for your F-82 experiences. Have run the motors in the basement (another advantage to electric!), they start and stop simultaneously, and seem to be in PERFECT sync - imagine that??? I am going to have to watch out to see that the props pull the same. They are APC-electric 6x4's but even though they are SUPPOSED to be mirror imaged and identical, they might have slightly different pitch.
You like???
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Dennis,
Looks really slick.
So do you think the 2s850(more or less) battery will be large enough for a full pattern or not?
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I can't wait to get in line to fly this baby. Bring out the 35' lines!!! I had a blast with the EP baby clowns!!! Bet it sounds great too!!! It is going to go like hell!!!!!
Archie Adamisin
Muncie, Indiana
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Dennis,
Looks really slick.
So do you think the 2s850(more or less) battery will be large enough for a full pattern or not?
THANKS Alan.
The Timer is fixed at 3 minutes, on a single motor and a 6x5.5 it draws 320mah. What I am perplexed about is HOW MUCH current will the twin use? I do not think the answer is 640 mah. The "work" being done is not much more than on the Baby Clown single, that is the F-82 is about 30 squares larger, roughly the same airfoil thickness, and 3.5 oz heavier than the Baby Clown. Plus (for now at least) it has 6x4's which will draw less current than 6x5.5's. My "guess" is that it will not draw that much more than a single, and that the extra current will mostly be due to the fact that I have two sets of motor inefficiencies to deal with (that make sense?)
I'm sure that a flight or two of DATA will be worth a couple pounds of speculation!
Did I mention how easy it is to start, stop, and sync the motors ;D
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Quote: "What I am perplexed about is HOW MUCH current will the twin use?"
I have been wondering this myself. Exceeding the discharge rate of this battery can be very dangerous. There was a good article in Fly R/C a number of years ago regarding how to wire a multi and formulae regarding different arrangements including running off a single pack.
Remember that the current draw will be virtually twice normal with two engines. A larger pack with a higher discharge rate may be the answer or two separate packs both of which will give a weight penalty.
I no longer have that issue of Fly R/C but I believe it was Bob Selman who wrote the article. A very learned man in electric power for small models.
Robert
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Hi Robert, good comments. I think I am safe on battery capactiy:
* If the current draw is DOUBLE the single on the same battery I should be safe: 2 x 320 = 640mah = 75% of capacity on the 850 pack.
* Since (at least for now) I have lower pitch props (6x4's instea of 6x5.5's) the current draw should be less - which is safer yet.
* Finally, (and for me this is the speculative/perplexing part) since the two motors are not required to do double the amount of work, the current load from each motor should be LESS. Again this should be safe
(I think!) ??? :o
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I will be watching this with intrest. Just a few days ago my lovely wife gave me a F82 for a birthday gift. I was not looking forward to fighting with 2 cox engines. I have a whole basket of parts, but black widow tanks, backplates and needle valves are in short supply. I considered 2 norvel's but the airplane is way too small for that.
Then I saw this thread. You can get small brusless motors for about what a cox glowplug goes for now, so I think this is the way to go. Since I already mess with RC parkfliers, I have the chargers and probally some batteries that would work.
check out hobby city for cheap brushless motors and batteries.
How is the balance? Becasue of the electric are there possibilities for putting the plane on a diet?
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Geez Dave with your park flyer experience this ought to be the proverbial no brainer for you!
The airframe, covered without any hardware on it weighed 5 oz. I think the fuselages could have had some lightening holes added I probably could have carved some weight off the plastic firewall mounts too, but frankly the pay-off is pretty small. BTW the kit built wonderfully - excellent diecutting and pieces all fit fine. I'm optimistic you will enjoy building yours.
The two Arrowind 2205 motors weigh the same as ONE Black Widow. My best guess is that the total power system weighs about 1 oz more than dual Black Widows would have.
The lither electric motors made the balance turn out a lot less nose heavy. THe combination of lighter motors and putting the battery on a pseudo drop tank below the wing also improves the vertical CG by a LOT.
We are in the midst of catz & dogz kinda weather, with more of the same plus wind predicted for tomorrow; so the test flight is on hold for now...
DId I mention motor start/stop/sync are EASY??? ;D
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I was thinking about this motor, only 8$ each
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=2069&Product_Name=hexTronik_24gram_Brushless_Outrunner_1300kv
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Dave:
Small props seem to have to spin really fast to get anything done. The motor you linked to is a 1300 kv, I am using 1650 kv. I think the one you picked is going to need 3S to get the job done - and it will do VERY WELL on 3S, not so good on 2S. Might need to cut back to 5x4 props to keep the current draw under control to.
For 2S I'd suggest you look at a similar motor but with a higher kv rating...
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Yes I missed that, most of packs are 3Cell. So I look for motors about that Kv. Hobby city has many motors all under $20 with Kv's from 980 to 3000.
The quality is sometimes poor, but I have had good luck. Some have metal all over the internals, and the motor leads need some goop on the m for strain relief.
I like glow power better, my day job is an electric drive control engineer. I build software that control large 3 phase motors. My hobby is getting too much like my day job. :-[
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Dave,
The motor you listed runs great on 3S with a GWS 8x4 Direct drive prop. I bought one of these to use on an indoor ECL airplane. It is very efficient. Likes the GWS slow fly prop too. Pulls a measily 8 amps on 3S and either the 8 x 4 or the 7 x 6.
For the F82, might I suggest the Emax 2805 2800 Kv. It will handle the load and cost is $4.99 ea. They also make it in a 1600 Kv. I like the 2800 Kv cause it has some power. On 2S 5.5 x 4.5 props turn around 13,500 @ 12 amps static.
Archie Adamisin
Muncie, Indiana
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That's really neat!! I have one that has 2 Cox 049 on it that is hanging up for the last 10 years or so that I never flew. Now you're giving me a reason to take it down and do something with it. I bet it will be a fun plane.
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William,
Dennis sent me some pics of his airplane today. I gave him some of the set up and flying parameters that I am using for my F-82. Get yours down off the wall, get the engines running and take it out to fly. For reference, I am using .012"x35' lines (maybe a hair fast), 2 twin port Golden Bees with Tornado 5x3s running 10-29 all castor fuel. Make sure you have a good amount of deflection in the elevator and that the push rod is well supported and take it out for some fun. Mine weighs in at 11.5 ozs and can loop inside, outside, do lazy 8s and fly inverted without any problem.
John
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Hi Dennis,
Very nice fun project. :-)
I don't mean to hijack your 1/2A thread, and maybe you should ans. my question in the building or design section?
Do you have any close up photos, and details of your neat looking take-apart system for your profile? I want my new profile ECL plane to be a take-apart, but I don't want to reinvent the wheel if someone has already done it. ;-) ..... TIA
Regards,
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Hi Dennis,
Very nice fun project. :-)
I don't mean to hijack your 1/2A thread, and maybe you should ans. my question in the building or design section?
Do you have any close up photos, and details of your neat looking take-apart system for your profile? I want my new profile ECL plane to be a take-apart, but I don't want to reinvent the wheel if someone has already done it. ;-) ..... TIA
Regards,
Oooops: there is no take apart. I covered everyting in pieces, then assembled like an ARF. Easier to cover that way...
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Oooops: there is no take apart. I covered everyting in pieces, then assembled like an ARF. Easier to cover that way...
Bummer Dennis, I was getting so excited! I hate to reinvent the wheel when there are so many people around me that are much smarter than I am! :! ..... well, back to the drawing board. n~
Regards, H^^
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The F-82 has flown - and I can report YEE HAW!
First the easy stuff. THe two motors weigh the same as 1 (dry) Golden Bee, the battery is installed even with the wing - putting it just a smidgen behind the CG. Thus the CG was well aft of a IC version, but it flies very nose heavy. On 35' lines there is plenty of power for manuvers, but it will only turn 90 degree loops! inverted flight and LARGE lazy eights quite doable. It will not do very much but, being a twin, every thing it does is quality time.
Last flight I used a 3S instead of 2S battery and moved it aft as far as I could on the battery mount. Speed went way up (duuuuh!) and it pulled a lot harder. turning radius did not get much beter, but it was easier to turn. WIth the 3S pack it was going fast enough that it would probably have flown on 50' lines, no doubt it would be happier flying in the bigger sky...
Really cool with the simultaneous starts and shut-offs of the twin motors, actually it behaves like a single but still has that twin sound!
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The F-82 has flown - and I can report YEE HAW!
First the easy stuff. THe two motors weigh the same as 1 (dry) Golden Bee, the battery is installed even with the wing - putting it just a smidgen behind the CG. Thus the CG was well aft of a IC version, but it flies very nose heavy. On 35' lines there is plenty of power for manuvers, but it will only turn 90 degree loops! inverted flight and LARGE lazy eights quite doable. It will not do very much but, being a twin, every thing it does is quality time.
Last flight I used a 3S instead of 2S battery and moved it aft as far as I could on the battery mount. Speed went way up (duuuuh!) and it pulled a lot harder. turning radius did not get much beter, but it was easier to turn. WIth the 3S pack it was going fast enough that it would probably have flown on 50' lines, no doubt it would be happier flying in the bigger sky...
Really cool with the simultaneous starts and shut-offs of the twin motors, actually it behaves like a single but still has that twin sound!
Twin sound? I thought electrics were quite. LL~
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Quite quiet.
The props however are every bit as loud.
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Good one John! LL~ LL~ LL~
Of course Ray is right on target - the sync sound is from the props - plus the 14 pole (Twin Wasp???) firing pattern!
TOp it all off, I wear hearing aids - by the time I get to the handle 35' away from the F-82 it is Pretty Darned Quiet!