Startup failure at load

[TKara.2]

I profiled my motor using the Profiler application while it was not under load. Afterward, I used the obtained values to generate new software. However, during testing on the motor pilot application, the motor does not start under load, regardless of whether it’s in torque mode or speed mode. When it’s not under load, there are no issues. Do I need to perform PID tuning?

here are videos under load and not load https://youtu.be/hOYXae-8l-M?si=RV6EAJ2st8wsGWhU

https://youtu.be/sTGa2zcNCKY?si=5_LyxKUZ59Qp4z13  • The Profiler application cannot obtain values when the motor is under load.

[TKara.2]

Do I need to use open-loop control for a better startup?

[Gael A]

Hello TKara.2,

Let's first clarify a point :

Motor Profiler is used to get your motor's characteristics. Those characteristics do not change whether the motor is loaded. Exceptions are made for inertia and friction of course, but those are only used for speed PID gains computation. Thus, the Profiler should always be used on the easiest of conditions, that is without any load.

Concerning your issue, at first glance, it looks like everything is working fine : under load, your motor may not turn but the MotorPilot does not return any error, and current is drawn up to your maximal value (50A), it just looks like your load is too high for the input current. However, your power output is a bit strange. At 72V, a 50A current would give you a much higher power value than 80W. Plus, it really looks like on your video that the torque is rapidly lost, with no effective power. There are two different solutions to this :

- Your current is wrongly estimated, which is unlikely since your motor is running nicely once unloaded. Having a look at the current curves would still be a good idea though. You can do that by using the datalog feature on the top right of the Motor Pilot.
- Your VBus is dropping, which can happen undetected only if you are using the Virtual Vbus feature. Is it your case ? If yes, then it means that your power supply may be at fault here, or limited.

[TKara.2]

Hello @Gael A, thank you for replying.

Here is my VBUS feature schematic.

I’m using a Li-ion battery pack (20S10P configuration).

I’m struggling to understand why the output power (W) does not increase under load. This issue occurs in both speed mode and torque mode. When the motor is not under load, I can provide a 50A reference in torque mode and get a corresponding power (W) output. However, under load, it seems like the battery or the software cannot provide the required power (W) momentarily.

When the motor is under load, I expect the inertia and friction forces to increase. Therefore, shouldn’t I adjust the gain? Would PID tuning help resolve this issue?