Energy recuperation

Hi,

Is there regenerative power in the SOLO module-uDriver setup? If so, how much?

We are using the SOLO modules on a bipedal robot with springs and in part of the gait cycle there might be some energy recuperation from the modules measured with external current sensors connected to the power source of the uDrivers.
Also, we connected a small DC motor to the power input of the uDriver and turned the SOLO module by hand. Turning the SOLO module by hand in either CW or CCW direction resulted in CW rotation of the connected DC motor, so there has to be some small amount of current going back to the system but when we measured this, it was very small, in the range of noise.

My question is, what is happening with the returning current on the uDriver, does it go to resistors/capacitors so that only a small amount goes back on the power line? Did you do any measurements on the energy recuperation efficiency of the SOLO modules?

Thank you for the help in advance!
Bests,
Bernadett

Hi Bernadett,

I got to know your work https://arxiv.org/pdf/2203.01588.pdf, nice motions!

Regeneration can happen when you command a current Iq that is opposed to the velocity sign.

When not powered on, the uDriver can allow regeneration current (that you observed in your test)
but this is much lower. Indeed, The driver just act as a 3 phases full bridge rectifier formed by the parasitic mosfet diodes. In this case, you need to have a voltage higher than the diodes forward voltage (so some velocity), and a load that can absorb the current at low voltage. For your robot setup, this would mean that you need crazy speed to reach a BEMF higher than bus voltage to charge the battery or simply help to power other axis.

Instead, when you actively control your joint with a control low that makes the power negative, you will see proper regeneration. You can try for example

Iq = -Kd * speed

with Kd>0

To see the regeneration, you should monitor input current and voltage of the uDriver when applying mechanical power to the joint.

We never quantified how much we could recover from the uDiver yet. Power loss are expected due to the motor coil resistance and uDriver logic consumption.
Please keep us posted!

Hope this helps,

Best,
Thomas.

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