3 ms·

> Complex in that they built so much more functionality into the device than was really needed. This thing is covered in sensors; it's got two scales, ostensibl

> Complex in that they built so much more functionality into the device than was really needed. This thing is covered in sensors; it's got two scales, ostensibly for measuring the weight of the hopper and the weight of food dispensed, a pair of infrared sensors to detect when the hooper is empty, sensors that monitor the motor's turning, and others that I haven't figured out the purpose of. I'd love if Surefeed, a competitor, had gone the way of shipping more sensors. Instead, they just monitor the current going through the motor to detect if the lid is closed or opened (the current will spike when it reaches either end position)... and the motor is relatively powerful, powerful enough in fact to shred the plastic gears. It's laughable - this thing consists of a few pieces of plastic, an RFID antenna loop, a motor and a tiny PCB, but costs 160€.

stavros 3y ago
A current sensor is much better than a position sensor, as you don't want to keep trying to close the lid if it catches on anything.
- mschuster91 3y ago
  A rotation sensor would detect a blocked gear just as fine, maybe even faster than a current monitor - with the advantage of the rotation sensor being unimpeded by slack in the gear train.
  - stavros 3y ago
    Why is the current sensor impeded by slack? It's also much cheaper and more reliable.
    - mschuster91 3y ago
      By the time the current monitor senses the spike, a lot of tension can build up in the gear train from slack and torsion. A rotation sensor on the outermost axle can detect a blockage way earlier.
      - londons_explore 3y ago
        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.

stavros 3y ago

A current sensor is much better than a position sensor, as you don't want to keep trying to close the lid if it catches on anything.

mschuster91 3y ago
A rotation sensor would detect a blocked gear just as fine, maybe even faster than a current monitor - with the advantage of the rotation sensor being unimpeded by slack in the gear train.
- stavros 3y ago
  Why is the current sensor impeded by slack? It's also much cheaper and more reliable.
  - mschuster91 3y ago
    By the time the current monitor senses the spike, a lot of tension can build up in the gear train from slack and torsion. A rotation sensor on the outermost axle can detect a blockage way earlier.
    - londons_explore 3y ago
      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.