Hi,
Apologies if this is a silly question but I can't seem to find the answer. My application is an electric constant torque winch, motor will be sensored or encodered as required using FOC. The operator would request the motor apply a specific torque to the winch, say 50Nm. The load on the winch is dynamic meaning it may exceed the motor applied torque, how does VESC behave when this happens? Ideally I would want the motor to still apply 50Nm torque and the motor will decelerate and start to turn the opposite way (the winch would pay-out) since the load torque would be greater than 50Nm. In this way the force on the winch cable remains constant irrespective of the load.
I guess on a skateboard the hypothetical equivalent would be what happens if you are going up a constant incline at constant throttle and gain mass (somehow) until the torque is insufficient to continue climbing, would the board stop and then if you gained even more mass would it slowly start to roll back down the incline?
Thanks,
Joe
You just need to set your VESC to current control mode. Motor torque is proportional to current. You can get 50Nm from a large high torque direct drive ebike motors or using geared motors (beware many geared motors have integrated freewheel). If the load on the winch exceeds the torque set by your current setting, your winch will unwind the cable, and opposite if the load is lower. The motor inertia will play a role, the the cable tension will not be perfectly constant (unless your motor inertia is very small)
Anyway, you need to take care what happens when all the cable has wound/unwound from the winch... You could also adjust your current setting as a function of motor turns, to stabilize.
An encoder and FOC mode is a must to get smooth operation, even at lower speeds and especially while changing the direction of rotation
Thanks for the details.
There is an overall management system running controlling limits, measuring rpm, absolute tension, line length etc, the VESC would just form the torque actuator part.
I'm mainly interested in the case where the load on the line is greater than the torque applied by the current control loop of the VESC and the winch is therefore paying out. In this condition the controller is still driving current into the motor windings (this is not regen braking correct?) , is there excess energy within the motor from the external load driving it (like a generator), if so where does this go?
Thanks again.
What sort of gearing will this winch have?
A motor can be back driven with motor predictably resisting the movement as long as the gear ratio is 1:10 or less. I think this is called "pseudo direct drive." One of James Bruton's recent Open Dog YouTube videos discusses this. If you're interested, I'd probably be able to find the exact video where he talks about this.
While the torque a motor produces is proportional to the current, a gearbox complicates things when it comes to back driving the motor.
Duane Degn
When your load overcomes the motor torque at very low speeds, the controller will draw power to maintain torque. If the load continues to drop and pick up speed, then the reverse torque will result in regen braking. The speed where the controller transitions to regen is quite low, probably a few percent of maximum.