Author Topic: HellCat Profile - with gear drive (Read 1944 times)

Dennis Adamisin · « **on:** June 11, 2009, 07:10:22 AM »

I had posted this before but that post got lost in the server crash. Now that it has flown I thought I'd re-show it.

Brodak Hellcat (profile) 53" span, 540 sq in, approx 42 oz
This is an excellent kit; all laser cut, parts fit is of course superb, assembly was pretty darned simple. Only changes made were those to needed to accomdate the motor unit. Color scheme is not scale but sorta copies elements of 1960's Navy (Skyraider) with the red tail of the 1930's birds flying off Lady Lex!

Motor: Astro Inrunner with Superbox gear drive (3.3 ratio)
This is what really sets this bird aprt from the "usu;" electric fare. THe motor is actually left over from Archie's F5 Pylon Racing days. Its attached to an all-metal Astro Superbox and a 3.3 ratio. Set the gear lash per Astro's direction and added some silcone grease - a little dab will do ya! The question is: how will it respond and is the naturally higher effieciency of the Inrunner motor great enough to ovrcome the losses inherent in adding a gear set?

Phoenix 60 ESC
Will Hubin FM-4 timer
Rhino 4S x 2350 pack
11 x 5.5 APC-E
63' lines (eye to eye) Approx 5.6 lap time
1840 mah over 5:45

Test flew last weekend, airplane and power system work very well, albeit nosier than the normal outrunner. Even with the unusal power system dialing in e-power is really simple compared to IC. To me the gear drive sound kind of mimics a over-muffled piped motor system. Heck this may eve appeal to our IC bretheren (OK that might be a stretch) We wee flying in nearly dead air, and could hear it governing to keep up. at shutdown the prop QUICKLY brakes to a stop - hinting that the motor braking effort is amplified through the gear drive. If so this woulod seem to bode wll for governor-braking in windy wind-up conditions. We'll see.

It will be at the Fly-in next week...

Alan Hahn · « **Reply #1 on:** June 11, 2009, 07:27:39 AM »

That's a really nice clean installation!

As I recall, this is one of the Brodak Warbird series planes, so it's about the size of a Nobler---or is it a little larger like the P40??

Also even though your lines are ~3 feet longer than mine, your level flight time seems really slow to me. I guess you are comfortable with the time--for some reason I have never been able to slow down that much. Just a comment....

Dennis Adamisin · « **Reply #2 on:** June 11, 2009, 08:37:23 AM »

Thanks Alan.

One nice thing about the gear drive is that in its narrowest direction it is roughly 1" thick, that means a virtually "internal" installation in a 1" thick profile. Some of the battery packs will fit that way too. Wanted to do that here, but the Hellcat nose is a little too short to let everything fit.

The bird is larger than most of the Brodak warbirds but the wing is much thinner than the P-40. If I had to guess I would say it is a Nobler wing, modified to equal span. THe wing is low so an IC engine would likely generate some vertical CG worries. in that sense the electric installation is an improvement - because I put the battery about as low as it could go.

Archie & I were also surprised by the performance at that airspeed - especially since it was flying in dead air. We think the large side area is a big enabler. THe forward fuselage averages about 4.25" tall, and at the canopy it is about 6.5 " tall - that is a LOT of side area! We think that (and the light weight) is responsible for the low speed capability. THat side area MIGHT become a problem when the wind blows, hope that governor works!

Archie Adamisin · « **Reply #3 on:** June 11, 2009, 10:32:41 AM »

I was lucky enough to get the second pattern on the Formly known "Heck"cat. It flew really well. Very easy to fly. By far the best profile stunter I have ever flown. I don't want to classify it that way though. It did everything right.

Historically, we (Uncles Dennis and I) have set up our IC systems to fly in the 5.5-5.6 sec/lap on 63' lines. I had some birds that flew well @ 5.8. I would have liked the Hellcat @ maybe 5.4-5.5 in the dead air, but if there was any air at all, 5.6 was perfect.

We test flew it on the 10 x 5 prop and it was flying @ 5.4 (if I recall) that way but seemed not to have the authority upstairs. With the 11 x 5.5, no issues even at the slower lap time. Uncle Dennis added some tip weight & rudder offset and we were flying patterns.

The power-system worked very well. The motor is not laboring at all. Definately need to play with props, but as is really works nice.

Anyone wanting a natural ECL conversion kit, I would most certainly recomend this one. What a bird!!!

Dennis Adamisin · « **Reply #4 on:** June 22, 2009, 06:23:37 AM »

Well, I'm afraid the gear drive experiment hit a serious snag. On the TENTH flight the pinion was worn smooth. Not a very effective way to deliver motor power to the prop I'm afraid. Gear lash was set and greased per specs. Prior to the final flight there was some evidence of gear wear but I thought I could get two officials out of it - didn't.

The gear train is rated for 600W continuous, and we see maybe 300w peak loads, so it is not a simple overload; more likely it is some kind of dynamic misalignment or vibration (harmionic?) with the propo loading/unloading as it goes through square corners and such. At any rate, we need to add at least one zero to the flight durability score!

Gonna send the gear system off to the elves at Astro and get some help. I hope to get it repaired, then bolt it in again and fly up to 10 more flights with it and see if THEIR way works any better. I am not real optimistic at this time.

Of course there are alternatives, it would not be THAT painfull to hog out the nose for an outrunner...

Alan Hahn · « **Reply #5 on:** June 22, 2009, 07:53:56 AM »

What was the gear material?

Dennis Adamisin · « **Reply #6 on:** June 22, 2009, 07:57:48 AM »

Quote from: Alan Hahn on June 22, 2009, 07:53:56 AM

What was the gear material?

Brass pinion and steel (stainless?) driven gear, helical cut. Driven gear does not show any obvious signs of stress, pinion is toothless! Pinoin is roughly 3/8 long with a 1/4" wide strip missing in the middle whre the driven gear resides...

Dean Pappas · « **Reply #7 on:** June 22, 2009, 09:36:25 AM »

Hmmm,
Methinks we should either be running a steel pinion against a larger soft metal gear like brass, or better yet a steel pinion against a "maintenance item replaceable" hard urethane or Delrin gear. That would be quieter too.
What's the motor RPM in this setup? Under 20,000 RPM? Round-toothed belts would be an excellent option.

The reduction system has a lot to offer, so I think this is worth pursuing.
Dean

Alan Hahn · « **Reply #8 on:** June 22, 2009, 10:02:10 AM »

Back when I was flying a RC Helicopter, I was always surprised to find white flakey things on the inside of the Plastic body shell. Eventually I realized it was the Delrin main gear that was being eaten away by the aluminum pinion gear. What was particularly surprising was that the aluminum pinion gear teeth had a sharp knife-like edge---the Delrin was apparently sharpening the aluminum, which then reciprocated the favor by slicing the Delrin. So I replaced the aluminum pinion with a a steel one, and of course a new Delrin gear too. Also made sure about the gear lash after that.

It's amazing what moving parts can do to each other!

Dennis Adamisin · « **Reply #9 on:** June 22, 2009, 11:01:17 AM »

Dean: Prop at 9,500 RPM with 3.3 reduction so motor is at 31,350 RPM (whew!). Noisier than an outrunner but not obnoxious - I think Astro originally went to helical cut to reduce noise versus straight cut gears. I cannot say for sure what the mechanisim of failure was.

Belt drive holds promise, and outrunners are a sure thing. However I do not want to run away from the promised efficiency of an inrunner just yet...

Alan: after you went to the steel & delrin, did you have to change-out on regular basis? I do not think Astro has an alternative gear set for any of there gearboxes, so something else would have to be adapted.

Robert W · « **Reply #10 on:** June 22, 2009, 11:56:08 AM »

Hi Dennis

It was nice meeting you and watching the plane fly at Brodaks'. I can not remmember if your model blipped at the end of the flight, so if this is not the case please ignore my thoughts. After reading in another post about the blips at the end of the flight adding stress to the gears if cycled fast, I could see this giving a reverse loading on the gear tooth. Now the question would be what is the real force imparted to the brass tooth?

Regards
Robert

Archie Adamisin · « **Reply #11 on:** June 22, 2009, 01:12:27 PM »

I have flown the Astro 710 on several sport RC planes without failure using both an 02 & 05. When he called and told me it failed, I was speechless. But now we know and we move on to fix it.

I like the belt reduction idea. Better for tooth engagement, better for dealing with high loads, and much quieter. I have used a Modelairtech belt drive on a speed 400 semi scale plane and it worked well. I remember the Kieth Shaw's big EP Bearcat originally flew with a belt drive and it was scary quiet.

I still believe that even with the added complexity, the reduction idea using an in-runner is valid. The added efficiency of the motor and I believe the added governor sensitivity with the 2-4 pole motor will show it's face. The Hellcat was truly a constant speed airplane. I attribute that to the Gear drive. Not to say that outrunners don't do a good job, but ask how many EP F3A airframes use outrunners. No one that I have talked to. Everyone uses in-runners with gear drives. (Dean, please jump in here) Heli guys use belt driven tails and have great success with it. There is learning here.

We'll have to see where this goes. Fix for the Hellcat coming soon.

Archie Adamisin
Muncie, Indiana

Dennis Adamisin · « **Reply #12 on:** June 22, 2009, 01:43:08 PM »

Quote from: Robert W on June 22, 2009, 11:56:08 AM

Hi Dennis

It was nice meeting you and watching the plane fly at Brodaks'. I can not remmember if your model blipped at the end of the flight, so if this is not the case please ignore my thoughts. After reading in another post about the blips at the end of the flight adding stress to the gears if cycled fast, I could see this giving a reverse loading on the gear tooth. Now the question would be what is the real force imparted to the brass tooth?

Regards
Robert

RW:
Yes I enjoyed meeting you too and enjoyed our conversations. My end of flight warning consists of a power down from 9600 rpm to 8000 rpm for a couple seconds followed by a power up back to 9600 rpm.

However, you might still be on to something.

With the governor trying to keep speeds constant the motor is alternatively pushing the prop or retarding the prop speed. Off the top that does not sound like the "smoking gun" but since the demonstrated failure is 10 flights, all ideas are on the table!

I did notice that when the motor shut off and the prop brake set, it seemed to stop the prop faster than an outrunner does - as if the motor working through the gears had a advantage for prop braking.

Alan Hahn · « **Reply #13 on:** June 22, 2009, 03:09:35 PM »

Now that I think about it, I wonder if the governor might be part of the problem. If you were normally flying around burning RC holes in the sky, you tend, I think to always be driving the prop with a positive forward load. If the aerodynamic load decreases, then the motor simply spins faster (assuming the throttle stays constant. So the gear teeth would tend to always be contacting on one surface (until the throttle is lowered, but we are talking about relatively slow variations of the gears slopping back and forth on each other.

With choppers, the blades represent a pretty big flywheel and so I am also thinking the gear load would tend also to be positive.

Now we come to our application, where our flywheel is pretty minimal (especially for all those who like those light props!

) and I know a lot of you have really boosted the governor gain up there. So I bet the motor torque is really jumping back and forth as the ESC tries to keep the rpm constant. Which means, I think, that the gear teeth are constantly rattling back and forth (at high frequency for sure so you probably can't easily hear it). However the brass pinion probably is just being eaten alive by the constant whacks from the steel teeth.

Seems reasonable to me since that gear was eaten up pretty darn fast! I can't imagine a metallic gear wearing away so fast without something going on at high frequency. Even my old Delrin/aluminum setup lasted a fair length of time. I didn't have an issue with the steel pinion /delrin gear afterward.

My solution would perhaps back off a bit on the governor gain (as long as the rpm plots look reasonably flat).

Dean Pappas · « **Reply #14 on:** June 22, 2009, 03:22:57 PM »

back off on the governor gain? Heresy!
Hi Alan

Dean

Archie Adamisin · « **Reply #15 on:** June 23, 2009, 10:33:19 AM »

I had the oppurtunity to talk at length with Patrick about the Castle governor gain while at the Toledo Show. What he told me was set the governor gain as high as possible until the motor started to chatter and then back it off. It works similar to a Heli gyro when you adjust the gain until the tail hunts and then back off. Since taking this approach, we have turned the gain back a bit on the outrunners and they got smoother. The gain was set to default on the astro geared motor and it seemed to hold steady. The Astro is a much higher inductance motor so that makes sense. It is a 4250 Kv as well which is high for the 3.27:1 (36/11) ratio on 4S, but it worked.

The reduction seems to work by just dividing out the Kv by gear ratio and that would point you the correct Kv. In this case 3000 Kv would be in the sweet spot in this configuration. I have a 3T Astro which is in that sweet spot range for Kv @ that ratio.

I look forward to more testing. I hope that Castle releases the ICE controllers soon so we don't have to lug around the Eagle tree loggers for Data.

Take Care,

Archie Adamisin
Muncie, INdiana

Will Hubin · « **Reply #16 on:** June 23, 2009, 07:56:07 PM »

Here's the Hellcat on its flight at the Brodak contest, Day 1, which began very well...

Dennis Adamisin · « **Reply #17 on:** June 23, 2009, 09:01:24 PM »

Now THAT is a great picture! THANKS Will!

Seems like the task at hand is to make the electric Hellcat drive system as dependable as the prototype's R-2800 (no small task!)

Dave Adamisin · « **Reply #18 on:** June 24, 2009, 09:15:28 AM »

Looking at the elevator it looks like it's in the bottom part of s round loop......

Dean Pappas · « **Reply #19 on:** June 24, 2009, 09:45:36 AM »

Hi All,
Hi Archie,
Yes, the geared motors have been dominant in F3A early on, but things are now about 50/50 geared vs outrunners, and the reason is noise and maintenance. soft mounts, curiously enough, dramatically improve gearbox longevity in Pattern ships. I still think that a belt or urethane gears offers an ideal compromise.

Dean

Author Topic: HellCat Profile - with gear drive (Read 1944 times)

Alan Hahn

Alan Hahn

Alan Hahn

Alan Hahn

Dave Adamisin