Yet Another Brushless Switchback Thread - Page 4 - RC Groups
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Sep 28, 2002, 09:49 PM
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BEC's Avatar
Originally posted by rcflyer11
Have you taken any WhattMeter readings with this setup?

No. I'm a little hesitant to add that much length on the input side when there isn't even an input capacitor (18A MGM ComPro controller). I will have to do so sometime soon, though, and if I toast the controller I can raid the Scout for the Phoenix 25.....
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Oct 07, 2002, 03:15 PM
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BEC's Avatar

Flight report on "B" box and 10X7 SF, 8X1100 HECell NiMHs

Well, I got 10 Switchback Sport RG sorties at the Fall Celebration of Silent flight - all powered by either of two 8 cell HECell 1100 NiMH packs, the miniAC 1215/16 in the GWS "B" box, an MGM ComPro TMM-18e-3Ph controller and the APC 10X7SF prop.

All of them (save for one cut short by the motor pulling off of the stick, but fortunately not departing the airplane - thank you tight 3-pin Deans connectors) were between 10 and 12 minutes long. Battery packs were only a little warm, and the motor seemed not to get too hot either even though I've not yet put a cooling air exit into my plane as we've been discussing in this thread.

How does it fly set up this way? WOW ! While it does not have "unlimited vertical", it can go straight up early in the charge longer than I can keep it going straight with the rudder and elevator (AUW is 16.5 ounces). Insides and outsides are as big as I want and feel effortless. It got to where my favorite way to demo the plane was to take off (two, maybe three airplane lengths), pull to vertical, pull up the gear while going straight up, pull over to inverted flight, and then push in a big half outside loop to straight flight, followed by, as I said, 10 to 12 minutes of serious fun.

After about half the charge the vertical capability is down to a couple of hundred feet, but everything else is still big fun. At about 2/3 throttle it flies like the 9X6SF on 8X720s fresh off the charge. If I left the stick there or lower I'm sure 15 minute flights would be easy.

I did LOTS of touch and goes in which the sequence went something like this: take off, pull vertical and retract the gear, do a stall turn, then one to three rolls on the downwind leg, turn base, put the gear down, float to a three point landing with just a touch of power, then do it again. When I was getting really brave it would be take off, pull vertical and retract the gear, pull to inverted on the downwind (right over the runway), then pull back to upright while putting the gear down, then land.

I let AirJer (Jerry Holcomb, local builder and pilot extraordinaire, and CD of the meet) fly it a bit on Saturday. I don't think I've ever seen such a grin on his face (and he was at the controls when the motor pulled free, but being the expert he is he shut the throttle down, dropped the gear, and made a nice landing practically right in front of us on the runway after this). I checked then reseated the motor and he put another 5 minutes on it, grinning widely. His only negative comment was "how can you do rolling circles on Mode II"?

As it happened he acquired a miniAC 1215/16 and an 18A Hacker Master controller from someone over the weekend and got all the details of the my SBS-RG setup before he went home yesterday afternoon.

Just about everyone remarked on the cool factor of the retracts and the outstanding performance of this setup.

I found myself repeatedly telling folks that they could probably get performance something like this out of a GWS EPS-C setup (Beaver/Zero) but that the motor would be toast in about two dozen flights. I'll have to fly a C box and see if I was telling folks the truth or not.

Doug, the next iteration's gotta have a screw to hold the gearbox to the stick and access for that. I thickened up the stick a bit with some thick CA Saturday night and flew all day Sunday, but noticed the gearbox was about 1/8 of an inch forward of seated when I put the plane away last night.

I'll put the Whattmeter on this setup tonight and see what the full throttle current draw is (and hopefully the long leads won't toast the ESC).
Last edited by BEC; Oct 07, 2002 at 03:25 PM.
Oct 07, 2002, 03:51 PM
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markwild's Avatar
Great Report!
What I'd like to hear about is a completely vertical takeoff. In other words, hold the plane in your hand pointing up, gear retracted. Then apply full throttle and let her go!
I'm gonna try it with my MiniFlash once I get a D gearbox, and I expect it will definitely do it once I get a MiniAC like yours.
Oct 07, 2002, 04:06 PM
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JBowling's Avatar

Re: Flight report on "B" box and 10X7 SF, 8X1100 HECell NiMHs

Originally posted by BEC
Doug, the next iteration's gotta have a screw to hold the gearbox to the stick and access for that.
Agreed. It makes a disturbing sound to hear the prop chew up the front of the plane. Glides amazingly well with it hanging off the front though. Happened twice on mine before I switched to the MiniAC motor.

Oct 07, 2002, 05:03 PM
89" Kool Aid drinker.
Smash McCrash's Avatar
I got a Whattmeter this weekend and put it on my MiniAC 1215/16 powered SB. Only defference in my power setup is the Castle Creations Phoenix 25 instead of the MGM. I was pulling 12 amps static at 97 Watts with an 8C NiMH 1100's.

I too had the motor pull off the stick and decided not to let it happen again. I put a small hole in the side of the fuse to allow a GWS servo mount screw in and screwed that sucker in place. I don't have any worries about it now. I did have the big 10" prop try to eat my plane and didn't like it. The plane does glide pretty well in that respect, though. A little CA and balsa and it was repaired. Not good as new, but acceptable.

Oct 07, 2002, 07:18 PM
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BEC's Avatar
It'll be interesting to compare Whattmeter notes. Motocalc predicts 13.5A (using the 600AE battery numbers).

I think I'm gonna have to put a screw in - the trick will be to make a neat hole in the side.

AirJer shut the throttle down almost instantly and there was very little damage to the nose of the plane from the prop - just a coupla dents in the cowl ring.

As many of you know, I like to do touch and goes and I probably cycled the gear 70-100 times over those ten flights..... and learned a couple of interesting things about the retracts. But that's for another thread, I think.

As for the hold it and let it go takeoff - sorry - for me airplanes with wheels are supposed to roll along the ground (however briefly in this case) then climb out. I suppose such a release would be possible, though.
Oct 07, 2002, 07:51 PM
A Clinger
rclark's Avatar
Here is my solution from day 1. Works very well and easy to remove. No screws to drop.... Just an 1/8" dowel and a hole.... A dab of silicone cement where dowel comes out the top to keep it there (just in case of course) and that's it.

BEC, I kind of thought you'd like the 10x7 ....

Also, I don't do touch and go's with retracts.... Once up they stay up until landing .
Last edited by rclark; Oct 07, 2002 at 07:56 PM.
Oct 07, 2002, 07:54 PM
Space Coast USA
hoppy's Avatar
I use a tooth pick so that it will act as a shear pin...........
Oct 07, 2002, 09:50 PM
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BEC's Avatar

My Whattmeter readings....

Just did a brief Whattmeter run with the miniAC 1215/16 and the 10X7 prop and the 8X1100 HECell pack.

After the intial peak I got:
4650 RPM

The initial peak was about what Motocalc says - 13.5A - but that lasted for only a brief moment. Sounds pretty doggone consistent with Mike's numbers. RPMs went up about 50 when I took the Whattmeter out of the circuit.

NOTE the battery voltage. 1.0V per cell - and this at the beginning (well 20-30 seconds into) the discharge. This tells me that we are pushing these cells pretty hard this way. Of course, in the air it unloads and the fact that I'm getting 10+ minute VERY satisfying flights, and the batteries are only warm upon landing, tells me that they seem to be up to it. How long they last only time will tell. These flight times, BTW, are better than the two sorties I did with these packs and the 9X6 prop even though the performance is up.

As for not shooting touch and goes with an RG airplane.....

If it's got wheels, I gotta ROG, and I gotta shoot touch and goes.

Granted, I'm a bit more selective with the surface with the retracts than I otherwise would be (no touch and goes from my very thick grassy home field unless it is FRESH mowed). But this weekend I had a smooth surface to operate on at the Fern Prairie Modelers field and I shot MANY landings. The SB Sport will slow away down and three point as pretty as you please if you try. And following a three-pointer by shoving the throttle back up, taking off and going straight up again as the wheels come up - well, I've never experienced anything like that before.
Oct 09, 2002, 04:53 PM
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Lefty and Leroy's Avatar
OK guys, after doing some research on brushless motors and getting a better understanding on how they work along with reading this thread several times I think I'm ready.

What do you guys think about this setup below instead of the /16

Motor: Model Motors Mini AC1215/20
ESC: Castle Creations Phoenix-25
Gearbox: GWS EPS-300C-B ratio
Pinion: stock from gearbox
Prop: ACP 9 x 6 or GWS 9 x 7
Batteries: 8 x 700NiMH

My thinking is that I'll get better performance than the stock GWS motor and longer run times. I'm not interested in hovering or unlimited vertical so I wondering how much less performance I would get by using the /20 instead of the /16? I want to keep using the same batteries I have but maybe not push them so hard.

Thanks for the help,
Oct 09, 2002, 04:59 PM
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BEC's Avatar
Motocalc says that will only pull 5A which will give you long run times and be nice to the cells, but may disappoint in performance.

When I first put the 16 turn into my SB's "B" gearbox I ran it on 8 720s and used the 9X6 APC-SF and performance with that setup was about the same or just a bit better than with the GWS motor (timing advanced) but at about an amp less draw, so the good performance lasted much further into the run.

The 20 turn motor needs a bigger prop or more volts. My opinion.
Oct 09, 2002, 05:04 PM
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Lefty and Leroy's Avatar
Thanks BEC What about putting it in a GWS "C" ratio with a 10 x 8 prop?
Oct 09, 2002, 07:27 PM
Senior Member
L&L - if you are not intending on using any "hotter" batteries than 8x700 NiMH, get the Phoenix 10 instead of the 25. You will only be able to yank 7-8A out of those cells, and would be much better off at 6A, IMO. Plus you go from .7oz to .3oz in controller weight and save $10. Of course, if you plan on using that controller with something that draws more juice, nevermind.
Oct 09, 2002, 07:35 PM
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BEC's Avatar
On the 20 turn motor I'd put the 10X7 APC on the B box. I'm curious, though, what exactly are you looking to do differently than those of us using the 16T motor? Higher turns means it wants more voltage (which is why I think the 20T motor would be dynamite on a three cell Li-Ion pack). But since the Rm is higher, the losses at a given current are higher.

The 16T, in the "B" box, with 8X720s and a 9X6 APC SF prop draws right at 7A. This is not what Motocalc predicts, that's what I get testing.
Going to 600AEs or 1100 HECell NiMHs gives a performance boost because they don't sag so much under a 7-9A load. Then adding a bigger prop to boot - well - that gets me to where I am today and boy was it fun last weekend .
Oct 09, 2002, 10:07 PM
Registered User
After further thought/reading, I decided to go with...

Motor: Model Motors Mini AC1215/16 (shaft diameter = 2.3mm)
ESC: Castle Creations Phoenix-25
Gearbox: GWS EPS-300C-A ratio
(so I can use an off-the-shelf 64p pinion)
Pinion: Robinson Racing 64P 16T
(centered on motor shaft with 3mm O.D. brass tube)
- GWS 8 x 6
- APC 9 x 6
- GWS 9 x 7
- GWS 9 x 7 (3blade)
- APC 10 x 7
Batteries: 8 x 720NiMH

I'm sorry I can't report any results yet, since I'm still waiting on
my ESC (ordered two weeks ago). Apparently, CC had a shortage
of ESCs after NEAT, so mine didn't ship out until yesterday.

L&L...if you're sticking with the Phoenix-25, you may want to
consider calling CC to check on their current inventory.

Good luck!

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