Motor Chatter & Backspin - RC Groups
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Aug 19, 2013, 04:00 PM
Fly It Like You Stole It !!
Paulbilbo91z9f's Avatar

Motor Chatter & Backspin

I need some help.

I'm having a sporadic problem with a motor and ESC setup on a 3.7M Electric Sailplane that I've just recently put together. The equipment I have is;

Hacker B40-12L Inrunner with a 4.4-1 Maxon Gearbox spinning a 17" x 13 Folding Prop.

The ESC is a Castle Ice Lite 75 Amp, and I'm running a separate Castle 10 Amp BEC for the servos and receiver. The Red wire is cut between the ESC and Receiver so no power is crossing between the BEC and ESC.

I'm running a 3S, 2,200Mah Battery.

My problem is, about every 3rd time I power up the motor it wants to turn backwards for just a second or two and it chatters like hell. As soon as it starts going in the correct direction it smooths right out and pulls GREAT! I've tried a different battery, but that is not the issue. I suspect it has to do with motor timing but I don't want to just start fooling with the settings in the ESC not knowing what I'm doing.

I have the ESC set for 80% soft breaking for the folding prop and auto detect for the Lipo Cutoff. It is also on the factory setting for the motor timing as I have not changed anything.

Any Advice would be great.

Thanks, MURPH
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Aug 19, 2013, 04:17 PM
JimNM's Avatar
Yes, motor timing is the problem. Set it to "high" or "hard" - then gently throttle up. Do you use the left stick or a switch to run the motor?

The esc is hunting for the right return signal from the motor, so that the esc will know "where" to send the pulse of electricity to turn the motor in the right direction. It is quite common to see power set chatter back and forth slightly. Go easy, take the prop off to reduce the load on the gearbox and let us know how it goes.
Aug 19, 2013, 04:50 PM
Fly It Like You Stole It !!
Paulbilbo91z9f's Avatar

Thank You

Thanks Jim,

I'll try it later tonight and let you know what happens.

Because I'm going to use the sailplane for ALES Competition I have the motor on the trainer button set for 100% power. The ALES timer only gives you a 30 second max. motor run to get to 200M altitude, so it's full tilt when I press the Trainer button and then motor"OFF" after the quick burst of 20 to 25 seconds at 100%. There is no "Soft Ramp-Up" on this system at all.

I'll let you know.

Aug 19, 2013, 07:26 PM
Fly It Like You Stole It !!
Paulbilbo91z9f's Avatar

It Works....

Hi Jim,

Okay, Here is what I did.

I got to thinking about your advice and why having the motor on a switch rather than a stick would make a difference. Obviously slamming the motor to Full 100% throttle with the push of the Trainer button just doesn't let the ESC spool-up the motor. After your explanation I started thinking about how I could bring the motor up to speed a bit slower but still use the Trainer button as my On-Off switch.


I am using the new sailplane program from Spektrum on my DX-8 transmitter. In the servo set-up part of the programming it allow me to set the servo travel speed, even for the motor. Bingo! I set the motor speed to 1 second and gave her a try.

That 1 second of servo timing gives the ESC a chance to start the motor spinning slowly and calibrate itself. Out of 20 tries, it only chattered once, and that one time was FAR less abusive than what it was doing before. If I slow the motor servo timing a little more, say 1.2 or 1.4 seconds, I'll bet it never shakes again.

Thank You So Much for Your Help!

Aug 19, 2013, 08:35 PM
JimNM's Avatar
That's why we are here, amigo. I was going to suggest that very thing. The gear box will thank you as will the ESC.

Good luck with ALES! I am very interested in that format, too.
Aug 21, 2013, 01:23 PM
Fly It Like You Stole It !!
Paulbilbo91z9f's Avatar

ALES & ESC Size?

Hi Jim,

While I have your attention I'd like to ask another question. I know if you under-size and ESC or battery you can damage them or your motor, but is it possible to "OVER-Size the ESC?

I'll tell you why I'm asking. A friend of mine blew out an ESC in his plane last week. It probably needs a 35 to 40 Amp ESC. He had a 100 Amp Castle Ice-Lite and put it in the plane. Now, when he tries to run it the motor fires up for about a 2 second burst and then the ESC shuts down and just signals and over-draw.

So.... Did he damage the motor when the first ESC fried????? Or is the 100 Amp just too big????

Any input would be welcome.

Also, This is my second summer doing ALES. I went to the Pole-Cat contest in PA back in mid-June and there were 58 pilots there for the 2 day event. It was a real blast and I had a great time. If I can return the favor and give you any pointers in how to get started, I'd be happy to.


Aug 21, 2013, 01:57 PM
JimNM's Avatar
Oversized esc will only hurt you for weight and size. Your friend's issue may be a cell count issue. Is his esc an auto detect or is it hard set to a known number of cells? Sounds like the esc is set to 4 cells and he is using a 3 cell. Initial power level on 3s will meet 4s voltage requirements for a second or two - then it will drop into LVC area.

Take a multimeter set to measure resistance - check two motor leads at a time a-b, b-c, c-a. The resistance should be very low. Then check each lead against the motor housing to see if there is a short. Usually a shorted winding will not let the motor run at all as it will confuse the esc (refer to post #1 what a confused esc will do )

Some esc will not work at lower voltage (i.e. 3-4s vs. 4-8s)- check to see that the battery meets the esc specs.

As far as ALES goes - I need people to fly that profile with. I have a couple of RAM units and even a couple of extra gliders. The glider guys around here are DLG addicts, getting them to stop spinning long enough to fly ALES doesn't happen often. I did set up a loose set of rules to play ALES like golf for an hours at a time on the field, so I can measure my progress against a "handicap" system.

Be well, amigo - let us know if you still have problems. I did stay at a Holiday Inn...
Aug 22, 2013, 03:44 PM
Registered User
peterangus's Avatar
Be aware that when the motor is "chattering", there is zero back EMF.

This results in very high current if you apply full throttle [about four times the max when running normally].

So, fitting an on/off switch rather than a progressive throttle, is not a good plan.

Keep the throttle demand low [until normal running is achieved], and monitor the motor temperature.
Last edited by peterangus; Aug 22, 2013 at 06:11 PM.
Aug 23, 2013, 06:49 AM
Fly It Like You Stole It !!
Paulbilbo91z9f's Avatar

On the Button

Hi Peter,

I hear your warning about not putting the throttle on a switch. However, the ALES Contest format that I'm flying makes it necessary to do so. I haven't had a lot of time to test it out yet, but the idea of simply slowing down the servo travel seems to work. (at least in the workshop) I assumed that slowing the servo travel time from the switch would be the same result as taking a second or two to advance a stick from 0 to 100%.

I'll let you know how it works when I get it in the field and give it a real life test.

Aug 25, 2013, 06:40 PM
Fly It Like You Stole It !!
Paulbilbo91z9f's Avatar

All Set !!!

Finally got out today and put the Aspire up for 3 nice flights over 20 minutes each. Ran the motor up to speed at least 8 times and did not have a bit of chatter. At full-power the Hacker B40 takes the 3.7M sailplane to 200M between 26 and 30 seconds. (Good time, but not great! I'd like to see low 20's on launch.) I have room to angle up the pitch on the prop and think I'm going to try going from the 17" x 11' to a 17" x 13' and see if it will shave 4 or 5 seconds off my climb.

Thank you both for your help and advice.


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