MMM cutting off prematurely
 

Hello, I have an MMM that I am using with the CC/NEU 2200 kV motor in my HB D8T. For some reason, the ESC cuts off prematurely. I thought that perhaps my cutoff was too high so I dropped it to 3.2V per cell. I am running brand new 5s lipo 5000 mah Turnigy packs. When the pack cuts off there is still 70% left in the battery. Also, the resistance of the pack is good, 1.2 milliohms per cell. Strangely, if I let it sit for a couple of minutes it just starts to work again and will run for about another 30% of the battery. I thought maybe it is thermalling so I checked the ESC temps and they are only around 140 and of course the fan never turns on that thing. Probably a broken wire like all the MMM's I have purchased. :lol:
I have tried different gearing and right now I am using a 13T pinion with a 50T spur which should put very little to no strain on my car. I am also using the elite RC motor mount which is similar to the Losi 8/T mount.
Other things I have tried was to update the firmware and change timing settings on the ESC through castle link. No luck.
The ESC itself looks fine. It is clean and mounting on the ESC end of the Losi battery tray so it has some flex to withstand some of the harsher landings. Any help would be greatly appreciated!! :smile:

Interesting- most people have the opposite problem with the LVC kicking in too late unless they raise it up around 3.4-3.6v per cell.

Umm, try dropping it down to 3.0v per cell, same as the auto-lipo setting, see what it does then; you should notice the power start to drop off as the lipo becomes depleted, so stop running it anyway if thne lvc hasnt kicked in by then- thasts what I do with my zippy-h lipos and I haven't had any issues thus far (The Force lets me know when the lipos are approaching ~3v per cell, but they still rebound back to about 3.3-3.5v once you take the load off them....).

Ok this is interesting I think the issue is with my motor somehow. First, I tried turning off the voltage cut off and the same thing happened to me. I then changed the ESC to the MMM in my 8ight and amazingly it still kept prematurely cutting off. I never had issues with my 2200kV CC motor and it was in my old HB lightening which I rarely drove. Guess the motor is somehow no good afterall even though the motor temps never reached above 150 degrees. Gonna try putting in a 1700 kV buggy motor I have to see if the premature cut off goes away. I don't get how the motor can cause the ESC to cut off like that. It's just weird because the ESC will kick back on after 5-6 minutes of inactivity. :oh:

Usually, if a motor is bad, it either will not run right or get hot for no apparent reason. But, if the motor was somehow bad (rotor partially demagnetized), it will pull much higher than normal currents, which will cause larger voltage dips therefore tripping the LVC. Could also check power connectors (on battery and ESC) to make sure there isn't a problem there, which would cause voltage drops on higher currents and trip the LVC early.

The motor feels strong. It doesn't cog or anything and the magnets on the rotor feel strong. I don't think it is the connection to the battery that is bad as I changed ESC's and still have the same problem. I can only guess maybe the leads from the motor causing too much resistance? Or perhaps the connections underneath the plastic cover on the motor are bad? :neutral:Also, I know the shimming between the pinion and spur is good and not loose. Also, the drivetrain in my car is very smooth especially with my elite RC mount.

Well, if the problem persists with different ESCs, then it has to be elsewhere. Some things I can think of:

1) The battery could just be weak, or maybe one cell is weak

2) The battery connector is dirty, worn (from hook-up spark, or just from use)

3) Motor is faulty. But again, this would usually be evident by the motor, ESC, and/or battery getting hot from the large current draws.

I would not suspect motor wiring because if the motor wires or connectors had a higher resistance connection, you'd probably have abnormal operation, which is pretty obvious. But anything is possible.

An eagletree device would probably help here. It won't tell you if the motor is bad per se, but it would show you the current and voltage points and can help you narrow the search.

There is some guys in the trx forum having issues with the turnigy packs coming unsoldered. Maybe its intermitent problem where when the batt heat up a little expansion break the conection. IDK Try different packs

same here dude....hmm....jedi?

After a cut off, if you go to off throttle and leave it there, and the ESC flashes green and yellow the ESC has hit Low Voltage Cut Off (LVC). It this happens prematurely the battery pack cannot maintain voltage under the load of the motor. You will need better batteries.

Bernie

Could your Rx be losing signal as well?
Just a thought of something else in there.