3 ms·

Current sensors can respond in microseconds if needed. Tension takes milliseconds to build up. I would say the current sensor is probably the right engineerin

Current sensors can respond in microseconds if needed. Tension takes milliseconds to build up. I would say the current sensor is probably the right engineering design for reliability, but clearly poor implementation choices were made in this case. An even better design is a BLDC motor with saliency feedback. That avoids brushes (wear component), and gives both angle and torque feedback. Unfortunately I think someone must have patented it because nobody uses such a design for cheap stuff, despite it being far cheaper.

numpad0 3y ago
That's complete overkill. Single BLDC driver can drive 3 DC motors each, even in both directions independently if combined with a dual power supply. I think positional readouts from BLDC is still incremental, so either an origin sensor or a separate absolute encoder is going to be necessary on top of current monitor for sanity check. Whereas, that sanity check current sensing channel could detect jams somewhere in the machine which in itself should suffice for detecting lids pressed against stops. If there were even a <350EUR cat feeder with that kind of controls and features - it'll be flying off the shelf into university labs and hobbyists sheds. There will be drones and 3D printers built on that. Perhaps even some guided missiles.
- londons_explore 3y ago
  Tiny BLDC motor controllers can be had for under 1.5 cents, plus a microcontroller (which most devices have anyway). (six 1 amp mosfets, plus a few passives, and about 1 cm^2 of board area)). Unfortunately they normally need a control loop that runs at at least 10kHz for saliency measurement, which means all the other code on the microcontroller needs to be well behaved and not have millisecond long critical sections. If you can't do that, you need to add another 5 cents for another microcontroller.

numpad0 3y ago

That's complete overkill. Single BLDC driver can drive 3 DC motors each, even in both directions independently if combined with a dual power supply. I think positional readouts from BLDC is still incremental, so either an origin sensor or a separate absolute encoder is going to be necessary on top of current monitor for sanity check. Whereas, that sanity check current sensing channel could detect jams somewhere in the machine which in itself should suffice for detecting lids pressed against stops. If there were even a <350EUR cat feeder with that kind of controls and features - it'll be flying off the shelf into university labs and hobbyists sheds. There will be drones and 3D printers built on that. Perhaps even some guided missiles.

londons_explore 3y ago
Tiny BLDC motor controllers can be had for under 1.5 cents, plus a microcontroller (which most devices have anyway). (six 1 amp mosfets, plus a few passives, and about 1 cm^2 of board area)). Unfortunately they normally need a control loop that runs at at least 10kHz for saliency measurement, which means all the other code on the microcontroller needs to be well behaved and not have millisecond long critical sections. If you can't do that, you need to add another 5 cents for another microcontroller.