I need some serious help! - RC Groups
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Apr 30, 2002, 04:12 PM
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ScotY's Avatar

I need some serious help!

A friend has a custom electric helicopter that he built about 10 years ago. It uses some Kalt components and is about the same size as a .30-.46 glow heli (depending on blades, rotor head, boom length). It weighs about 65 ounces with everything except motor/controller/batteries.

He doesn't really remember exactly what motor he used but he has a bunch of Astro 40 and 40 FAI motors in his shop. He says he used 24 cells! but this doesn't sound right for these motors. Anyway, specifics are pretty blurry at this point. He did say he could get almost 10 minutes of gentle flying using old technology Panasonic 1700ma cells. This is all he remembers.

Gear ratios that he has available are 11.3:1, 9.7:1, and 9:1. It can easily use .46 sized rotor blades. I'm thinking that due to it's relatively high empty weight, the larger the rotor the better and a relatively high cell count. He'd like to get a controller that he can stick with throughout his experiments but realizes that he may have to try several motors before he finds one that's ideal.

I really need some help to come up with suitable motors and controllers to recommend to him. He's a serious helicopter nut but has not done much with electrics. Somebody please help!
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May 01, 2002, 03:45 PM
ChrisS's Avatar
Look at the Actro line from Koehler (www.actro.de). I'd guess a 24 series in either a 3 or 4 turn stator. You should be able to make a good guess just using the tables on thier website.
The Astro's will work but will be marginal at best and prone to overheating. But then, if you already have them maybe it's best (or at least fun) to experiment a bit.
May 01, 2002, 04:08 PM
Our Daddy and Heli Junkie
Fred Bronk's Avatar
Yes, if you are going to put together an electric heli go brushless for sure!

The gear ratio is about the same as many helis out there of that size.

Look for a motor with around an 800KV for 9-10:1 ratio and 20-24 cells.
May 02, 2002, 01:49 AM
Registered User
ScotY's Avatar
Thanks for the direction, guys. I hadn't considered the Actro motors since they seemed too large in diameter. Can anyone confirm the dimensions? I did check on the website but the 24-4 which sounds like it has potential, didn't have a diameter listed. Also, where's a good place to order them?

May 02, 2002, 02:06 PM
ChrisS's Avatar
On their site there is a dimensional drawing of all the Actro's except the 32-x series. They are accurate. Order them from Koehler direct, I have gotten two motor sets from Reto and the transactions have been smooth. They do not take credit cards so you have to mail them a check but other than that his prices are good and turn around has been quick. He is very good about returning e-mails but remember Stuttgart is 7 or 8 hours ahead of the U.S.
At first you will probably gasp a little at the prospect of how to mount the thing into your heli. But once you get started, it's really easier to mount a motor from the back end than it is from the front like most motors...or at least I have found this to be the case. All you need to do is put a plate across the bottom of the heli, make standoffs to raise the motor up to the correct hieght from there and run the pinion through a bearing block. All parts are either sheet or lathe turned...no mill needed.
Diameter-wise, the motors are certainly no bigger than the engine that came out of there to begin with. I think I know the heli your friend is trying to convert, metal head with a cast aluminum seesaw, yellow bubble canopy...can't remember the name just now, (I converted one too, many years ago) and the Actro 24X series should fit without problem.


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