We are using a Neo Brushless motor for our lift system and when we were testing it this evening it began to smoke. We were stalling our lift for about a minute and this is when it began to smoke. Can anyone suggest anything to fix this? We are currently replacing the motor with a Mini CIM but would like to use the Brushless. The motor was also extremely hot, about 150 degrees F is our estimate.
Don’t stall the motor for a full minute is my suggestion…
First thing is no motor can be stalled for a full minute and expected to come out fine. Cims and mini-cims would still feel the effect.
You can supplement the need of stalling the motor by counter balancing the weight of the arm. Use some thick surgical tubing, a constant force spring or a gas spring. These will help get rid of the “weight” the motor would have to feel. If you add enough it could just float at that level.
We’ve gone back over our video and it looks like it was only stalling for somewhere between 30 and 60 seconds before it began to smoke. At this point we’ve decided to use the Mini CIM for now and we are wondering if this is a general problem with any amount of stalling with a NEO.
Stalling any motor to hold position is not good design practice. Each different motors have different characteristics that will determine how long they can survive a stall condition. A CIM can last longer than a NEO but a NEO can last longer than a 775pro so it is all relative.
To get better performance with a NEO I recommend using current limiting, as your stall time will extend with lower peak current. The other thing to look at is if you can lower the effective power of the system by using constant force springs or counterweight.
The best elevators run as fast as they do because the amount of work the motor/gearbox needs is low when you make your system weight lower.
What voltage were you stalling at? What is the gearing of the system and the weight on the elevator? As you can see at the Vex motor data page a CIM or MiniCIM will also release magic smoke if you stall one at 12V for a minute.
Did you have the motor’s internal Hall effect sensors hooked up to the MAX? If this is not connected, the NEO/MAX combination will draw a LOT more current than necessary, and I wouldn’t be a bit surprised if most of that was turned to heat in the NEO.
that is an exceedingly long time to stall a motor of any kind, even if the cims don’t immediately smoke they will build up greater internal resistance if you continue to do this repeatedly to the point of failure. I would really recommend balancing the lift with constant force springs, then you still have to stall to hold at a position, but you can greatly reduce the voltage and current necessary to do so saving the motor, another option would be to add a bike brake to the lift system to hold it in position, there are many ways to fix this issue, but overall just stalling a motor to hold position is a bad design choice.
These are good suggestions. Our arm is so well counterbalanced, and the gear reduction between the motor and arm big enough, that we don’t need to give it any power - the arm doesn’t move, regardless of where we put it. In fact, there’s about a 40 degree arc, centered around horizontal, where the arm won’t move even before we got the motor/gearbox on there.
Another option is to add a physical brake to the arm. Before getting it all assembled and seeing the behavior, we had planned to use a bicycle disc brake to hold the arm in place (in fact, there’s one in place on our practice robot, although it’s not being used). The disc brake would have let us easily hold the arm in any position and cut power to the motor.
Do not that a Mini CIM has less power and probably can’t take much heat either. I would recommend a CIM but you might end up replacing it thought competitions
You can run the motor sensorless?
For proper operation, no. Apparently it is possible to get something which initially appears useful to happen without the sensor: (Read OP, then skip down to post #9.)
The topic I linked.
To be absolutely clear, the NEO must have its sensor cable plugged in to the SPARK MAX to operate. SPARK MAX does not support sensorless brushless operation at this time.
As others have correctly pointed out, the heating is due to the very long stall.
I will speak to our programmer about it.
We experienced a very similar event with our Lift system. In our case the lift was being commanded via the USB interface (so no log file…) at less than 40% output for about 30 seconds when it began to smoke heavily. In our case I can confirm that the sensor lines were installed.
Stalling motors for any extended period of time (greater than momentary 1-2 seconds) has the potential to damage any motor. CIMs are super abuse takers, but expecting a NEO, 775, 550, bag motor, etc, to last for extended stalls is going to lead teams to not having a good time.
The exact time for a neo is going to highly depend on your specific robot design, max configurations, and the loading conditions at the time.