6 More Days to Zero-G: A Few Steps Forward, and Some Back

Sorry for the late update. We actually wrapped up a little early tonight since tomorrow is Mother’s Day. I had to prepare a talk for Church tomorrow, so I’m only now getting a chance to write a quick note for our loyal readers.

Progress:

  • We got the drive system components in as well as the ribbon cable.
  • We got the boom installed in the deployer, and the drive system components (belts and pulleys) installed.
  • With some help from Brian Bernhard, Forrest was able to get the microcontroller running the boom deployer motor driven by proportional feedback from a thumb potentiometer (like what the Wii Nunchuck has).
  • We were able to figure out a lot of how we’re going to do the HMI interface mounting. We still need to actually finish the design and fab of that piece, but we now have a good idea of how.

Challenges:

  • When we got the PWM control code problems sorted out, the pinch roller was adjusted too tight, and we stripped the teeth off of one of our three timing belts. In hindsight, with a 200in-lb stall torque on the gear motor, this shouldn’t have been too surprising. We’ll be trying to troubleshoot this on Monday. It may be as simple as just adjusting the amount of pinch on the belts, or it may involve some modifications to our drive system.
  • The ribbon cable was thicker than expected. It turns out that while the conductors were .009in, the cable itself was quite a bit thicker. We might be able to make it work as is, or may need to get a backup on order (maybe something like FlatWire or maybe something else). The challenge is that even if we can get it overnighted on Monday, that still leaves little time to integrate it.
  • Gripper hardware is on order, but the pads and hardware are unlikely to all be here before Tuesday. That doesn’t leave a lot of time for integration and/or hardware iterations.

While we definitely hit some snags, we also made a fair deal of progress. This will probably be a very down-to-the-wire ordeal again, but we’ve come a long way in such a short time.

Ok, I need to run. Happy Mother’s Day everyone, I’ll be back with an update Monday night. Hopefully with a successful boom deployment movie.

Comments
  • Ed Minchau
    Reply

    Is the boom a good insulator? If so you can probably dispense with much of the insulation on the ribbon cable with a rig consisting of a few rollers and a pair of razor blades placed at an angle to the cable and each other, spaced at precisely the thickness you want. The rollers are to keep the part being shaved in tension; you would probably pull the cable through the rig by hand.

    OTOH that Flatwire data cable is 0.015″ with no fiddling around. How much current needs to go through these wires?

    How about having twisted pair wires running along each edge of the boom instead? It would increase the width of the deployment mechanism slightly and probably require altering your guide mechanism a little bit to allow room for them, but you wouldn’t have to provide for the thickness of a ribbon cable in your reel. The wire bundles along the edges would be the same thickness as the boom. You could probably carry more current than on a thin ribbon cable, if you need that extra oomph.

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