4 More Days To Zero-G: Electronics Progress and Getting On Our “Go-Go-Gadgettude”

Good solid progress today.

Forrest and Kirk stayed late on Saturday night and made some major progress on the controls and electronics after I left. By the time we came in this morning, Forrest had the electronics to the point where we were able to run the boom deployer using the Wii Nunchuck controls. Forrest bypassed the circuit board in the Nunchuck, so we were able to directly use the forward and back potentiometer to control the PWM output from the microcontroller to the “Simple-H” H-bridge we’re using to control the motor. This allows us to deploy at various speeds both in forward and reverse.

Forrest and Kirk also got the 6-cell battery setup so we can actually charge it using our balancing charger. I made the silly mistake of assuming that a 6-cell LiPo was a 6-cell LiPo, and that the interfaces must all be the same–but alas, that would make too much sense. Fortunately they were able to make some modifications and now we’re able to keep using the charger we already had. I would’ve just ordered the other charger, but it would’ve taken too long. So I’m glad that got that working. That also allowed us to drive the system at the full speed we wanted to.

Forrest right now is working on putting all these things that he’s done on a breadboard and putting it into a more robust and compact proto-board that we can actually mount into the boom deployer. We still have the boom-end electronics to do after this, and the deployer to boom-end cabling, but the human controls portion of the electronics is going well. Forrest and Kirk also were able to spec out a thinner ribbon-cable with end connectors that should hopefully do the job.

Also, in order to descope a bit, we will be ditching the position feedback sensors for now. Our Gripper hardware is designed in a way that we can mount those later, but for this flight they won’t be on.

Boom Deployer Work
First, some youtubery:

As you can see, with the 6-cell LiPo pack driving it, the boom deploy speed is respectably fast. We’re still having some issues with the 1/4″ MXL (Miniature Xtra Light) timing-belt drive we picked. Relaxing the pinch rollers helped a lot, but we still managed to eventually strip the teeth again. Fortunately after doing some checking it looks like there are some XL timing belts that will still fit, but have about 2.5x the breaking strength. Also, we found some 1/4″ pitch belt drive as another backup.

We also got the sheetmetal parts back from the Kenray Corporation here in Lafayette. They turned us around those replacement brackets with PEMserts in them really fast. Hill Mfg out in California did a great job on their parts, but it’s good having more than one supplier who can do quick turns and good quality. Hopefully next time I can give them more advanced notice.

The main remaining tasks for the boom deployer, other than doing another iteration on the drive system, are making the battery mount and making the Human Machine Mechanical interface. We made a lot of progress on that last task today. We’ve got models now for the sheet metal, and we’ll be hand-fabbing that tomorrow. For the part that grips the Wii Nunchuck, we actually printed out a drawing on a 1:1 scale, and cut it out using some stiff Manila envelope material to test the fit-up:

Mocking-Up the HMI Structure

Our plan for tomorrow is to get some sheet metal locally, cut and bend it manually around the Wii Nunchuck, drill and tap some holes to secure the sheetmetal to the Nunchuck housing, and then clean the interface up using some filler material and shrink tube. We’ll also use that to mount the wrist cuff and the arm strap.

Gripper 2B Parts
We got the first of the Gripper 2B parts in today, including the rest of the brakes, the ball joint, and the Torlon “Bogie Links”. While I never heard for sure if they got them off, Wayne will hopefully be sending the rest of the mechanism hardware, and we should hopefully also be getting the rest of the sticky pads as well. If all those parts arrive tomorrow we should be testing the integrated gripper mechanism on the balls tomorrow, using Ron’s set of high voltage electronics. If that works out, we’ll have Wednesday and Thursday to implement our own set of the high voltage electronics and brake controls.