4 ms·

> Where did they get a shaft encoder with over a million counts per rev? The article says they put the encoder directly on the motor, before gearing it down.

> Where did they get a shaft encoder with over a million counts per rev? The article says they put the encoder directly on the motor, before gearing it down. So the effective resolution after gearing is magnified. But the encoder moves much faster accordingly, hence the need for higher speed / fpga decoding.

Animats 8y ago
No, the article says "Dexter’s optical encoders are placed directly on each joint, and have resolutions that aren’t possible with any other control system." The usual approach is an encoder on the motor, before the gear train. They probably have one too, so they can see what the motor is doing vs. the joint. Remember, none of this is rigid under load.
- cbames89 8y ago
  There's just one encoder per joint. The encoder disk is 3D printed and the cruft from the print is used to refine the encoder ticks. Instead of fighting noise they save a map of all the systematic noise and then can use a lookup table to localize. *I went to Vegas and built an arm with the founders.
  - fest 8y ago
    Like an optical flow applied for radial motion?
    - cbames89 8y ago
      Like optical flow in that features are used, not like optical flow in that there's one standard by which all measurements can be compared to.
  - ggm 8y ago
    Does this introduce risk of future noise (fluff, chad, whatever: it's industrial applications == dirt == hostile environment) being misread, and require recalibration? Not saying wontworkbecause. I think this calibration trick is very good and I am imagining it's applications to other things eg more precise disk head placement from noise maps of the interblock separation reads
    - cbames89 8y ago
      Ya recalibration is definitely a necessary aspect of this approach if the optical reading changes. For example if IR light levels change.
      - kevin_thibedeau 8y ago
        Which is guaranteed with aging.
- JamesMNewton 8y ago
  Encoders at the joint only. Motors are steppers, so we have some idea where they are but that is open loop.

Animats 8y ago

No, the article says "Dexter’s optical encoders are placed directly on each joint, and have resolutions that aren’t possible with any other control system." The usual approach is an encoder on the motor, before the gear train. They probably have one too, so they can see what the motor is doing vs. the joint. Remember, none of this is rigid under load.

cbames89 8y ago
There's just one encoder per joint. The encoder disk is 3D printed and the cruft from the print is used to refine the encoder ticks. Instead of fighting noise they save a map of all the systematic noise and then can use a lookup table to localize. *I went to Vegas and built an arm with the founders.
- fest 8y ago
  Like an optical flow applied for radial motion?
  - cbames89 8y ago
    Like optical flow in that features are used, not like optical flow in that there's one standard by which all measurements can be compared to.
- ggm 8y ago
  Does this introduce risk of future noise (fluff, chad, whatever: it's industrial applications == dirt == hostile environment) being misread, and require recalibration? Not saying wontworkbecause. I think this calibration trick is very good and I am imagining it's applications to other things eg more precise disk head placement from noise maps of the interblock separation reads
  - cbames89 8y ago
    Ya recalibration is definitely a necessary aspect of this approach if the optical reading changes. For example if IR light levels change.
    - kevin_thibedeau 8y ago
      Which is guaranteed with aging.
JamesMNewton 8y ago
Encoders at the joint only. Motors are steppers, so we have some idea where they are but that is open loop.