From: hutto@SMTC.engr.scarolina.edu (Brent Hutto)
Subject: Re: Electric Power Recomendations
Reply-To: hutto@smtc.engr.scarolina.edu
Organization: NIST Southeast Manufacturing Technology Center
Date: Tue, 26 Jan 93 16:26:00 GMT

In article <JMOONAN.93Jan26094904@ccv1.bbn.com>, jmoonan@ccv1.bbn.com (John Moonan) writes:
>
>	I'm a long time wet power flyer but this past summer I decided to build
>an electric powered glider for a change of pace.  Ended up building a
>Goldberg Electra.  Power is the stock motor with a Master Airscrew 2.5X1
>gearbox and 12X8 folding prop.  Battery packs are 6 cell 1400 SCR, 7 cell 1400
>SCR and 7 cell 1700 SCE.  It flys great and I've had a lot of fun with it for
>the last 6 months.  Has a good climb on the 6 cell pack and very good climb on
>the 7 cell packs.  Now the question:

    I have an Electra, too, but I've never put a gearbox on it. With a 6-cell
    1400SCR pack and a 7x4 prop, climb is marginal, but acceptable.

>	The motor seems to be drawing about 25-30 amps on a fresh charge. I say
>this because it blew 20 amp fuses after about 30 seconds of run but has not
>blown a 30 amp fuse yet.  Is this a reasonable current for this motor?  Would
>I be better off going to a 3.0X1 gearbox or a different prop?  Am still using
>the original motor (has about 40 flights on it) and wondering how much longer I
>can expect it to last.  Any suggestions for replacement motor (other then
>AstroFlight which are expensive) when the time comes?  Would some of the
>modified motors that the car racers use work?  How many turns, etc.??

    You are probably pushing the motor quite hard at 25 amps, but you're in
    no danger of burning it up on a given flight. You're probably OK as long
    as there is plenty of cooling air available to the motor. How long does
    a battery pack (of each type) run the motor?

    After 40 flights, especially at over 20 amps, the motor brushes are no
    doubt either shot or close to it. You can't conveniently change them so
    it is time to think about a new motor. Go ahead and run the Goldburg one
    until it won't run any more and then throw it away. It sounds like you've
    gotten you money's worth out of it.

    If you want an R/C car motor, stay away from so-called "ROAR Stock" or
    "Outlaw Stock" ones and get a motor without a lot of timing advance.
    Tower Hobbies sells Kyosho R/C car motors. Look for one with around 20
    or 22 turns of wire. The Kyosho LeMans 360ST is a fairly strong motor
    with bushings (no ball bearings) which is reputed to be very durable.
    Tower has it for 20 bucks a pop. As an upgrade, look for a motor with
    ball bearings and around 22 turns of wire. The Kyosho "20x2 On-Road"
    motor is around 30 bucks and should last a long, long time if you keep
    it clean and change the brushes after 20 or 30 runs (whenever they look
    worn). If you shop around, you can find a Trinity-brand "350 2WD" motor
    for 25 to 30 bucks (more like 40 bucks at a local hobby shop) which is
    an 18-turn ball bearing motor. This is a very good motor, although it
    would pull much more than 30 amps with your current gear/prop combination.
    Use it with the same prop (bigger fuse) for really strong performance,
    but be sure to keep it cool. Or, drop down to an 11-inch prop and you'll
    have a strong climbing aircraft and a motor that, with care, will last.

    I just mention the Kyosho motors because I happen to have a Tower Hobbies
    catalog handy. The important thing is to stick to 20 or 22 turns (or at
    the very hot end of the scale 18 or 19 turns) and decide whether the ball
    bearings are worth 10 or 15 bucks difference. FWIW, car guys routinely
    pull 30 to 40 amps for 4 minutes at the highest level of competition, but
    the motors don't last forever and it takes really, really good batteries
    to make the 4-minute run time.

>--
>
>					THANX, John Moonan
>					SYSOP, 495th R/C Squadron
>					Groton, MA

    You're quite welcome, hope it helps.
-------------------------------
Brent Hutto
hutto@SMTC.engr.scarolina.edu
Newsgroups: rec.models.rc
From: bob@harrier.demon.co.uk (Bob day)