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Power Systems Talk about motors, ESC speed controllers, gear drives, propellers, power system simulators and all power system related topics

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Old 08-17-2014, 04:18 PM   #1
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Default Motor cogging / stuttering

I've got an heli where the motor starts cogging whenever I turn down the governor speed. I've got a swith and whenever I command a lower rpm it starts cogging. It happens rarely but does happen when I don't touch the rpm switch.

Symptoms are I loose rpm at the tail starts oscillating whith a frequency of approx 3hz. Same thing happens on the ground without main blades. It's violent enough to cut the screw holding the main shaft on my mini protos 450 within 15 seconds.

I've changed booth the esc, the motor and the tail servo, same thing. Could it be the fbl module (beastx) or the receiver? Now I'm thinking that i should run it without tail blades. And without any load. But I doubt it will do anything.

Any ideas to help?
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Old 08-17-2014, 05:46 PM   #2
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Has the governor got adjustable gain? If so try reducing it.
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Old 08-18-2014, 12:17 AM   #3
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It's an msh 60a, I turned it down to both proportional and integral gain to lowest position. Same problem.

However I noted that problem
- Is not present with motor alone
- Is present even without tail blades
- The main shaft is bent.

So I suppose it comes from the vibrations the main shaft is causing. I'll replace the main shaft.
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Old 08-24-2014, 11:29 PM   #4
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I replaced the main shaft and it is still doing it.

I'm really lost as to what could cause this. It seems that the problem accumulates over the time the motor is run on one battery.

When I connect a new battery I'll get 10-30s of running the motor (without blades) without any problem. If I cut the engine wait for a minute and restart as soon as I get some rpm.

Also using low rpm helps avoiding the problem.

I disconnected all servos, no change.

What should I test next? Change receiver, fbl module? Isolation issues?
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Old 08-25-2014, 01:06 AM   #5
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Maybe the governed speed is faster than the system is capable of holding, hence why it's ok at lower RPM? Maybe the battery is tired and cant hold voltage under any load?
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Old 08-25-2014, 02:14 AM   #6
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AFAIK,"cogging" is usually caused by the esc.
I had that problem recently with the motor in my AXN,and the only thing that cured it was a replacement esc.
I tried re-setting the old esc with the programming card,but no joy,so i think it,s kaput.
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Old 08-25-2014, 07:13 AM   #7
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I'm assuming you've ruled out the obvious, that being a poor connection in one or more of the motor leads between the motor and ESC?

Might be at some RPM, those wires are vibrating, and with marginal connections,

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Old 08-25-2014, 12:31 PM   #8
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Default Re: Motor cogging / stuttering

@beaver @kyle As explained in the first post I've changed both motor and esc already.

@jetplaneflyer the rpm is around 60-80% of max

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Old 09-10-2014, 09:32 PM   #9
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After a lot of experimenting I seem to have found the problem.

It is running in a mini protos. It got a lot better after releasing the tension of the belt between motor and main shaft pulley. Then after changing two ball bearings (guiding the belt) that were not in perfect shape (but not bad shape either), the problem went away.

Interesting.
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Old 09-13-2014, 12:20 PM   #10
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In fact I didn't find the problem.

Now it sometimes stutter when I change from idle 2 to idle 1. It also stops totally whenever descend in an autorotation like speed. i.e. when there is no load on the blades.

It starts back up again but it tries several times before succeeding.

What could possibly cause this??
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