Saturday, September 09, 2006


Volumetric Model of GM8 Gearbox...

I spent the evening with calipers trying to get the better of the Solarbotics GM8 gearbox.

The green dots at the right edge of the gearbox are bolt holes.

If anybody needs a copy of the .aoi file of this let me know.

The point of this exercise is to design a mounting for the AS5035 shaft encoder chip and its magnet. Here you can see the chip in grey atop the yellow magnet. There's not a lot of elbow room for this sort of thing with the GM8 geometry. As I see it at the moment the problem is largely going to lie with the securing of the chip itself to a mounting block.

Here is a mounting block being designed. The green rods are positioning holes for bolts and the red ones feed holes for filaments leading from the AS5035 chip to the top of the mounting block. You can see the AS5035 chip embedded in the block.

Here is the mounting block seen from the top. The red rod with the rounded tip is to create a slot for the comms cable connecting the shaft encoder chip and the control board.

Finally, you can see the lid in yellow that locks down the filaments and comms cable.

Here are two exploded views of the mounting block and the lid.

Would you then recommend going with the G8 motor configuration, given your testing? I didn't see the option to order it with 12V motor on the internet site... have you been in discussion with the guys at solarbotics on this particular model?
I'm not recommending anything till I get one actually running properly in-place. All I can say is that so far it looks pretty good.

Solarbotics doesn't have the 12v GM8 and GM3 up on their site yet, but you can call Dan Gates there and order them at the same price as the 6v versions.
Okay. I'll hold off ordering motors for now. I'll just experiment with the motors I've scavanged from printers, etc. until you've run a few more tests. They should be adequate to let me know my electronics are working or not. Let us all know how they work out.
On second thought, buying a GM3 or a GM8 won't break your pocketbook. You do need some of those AS5035's to go with them, though.

I'm just a little gunshy, beagle, because I've bought NEMA 17's, Siemens gearmotors and Frankenmotors at considerable expense thinking that all those were the way forward and getting it wrong for one reason or another every time. As a result, I'm feeling a bit like the little boy that cried wolf.
Well, I'm still holding out for an optical encoder.

If I need to put it at the drive shaft end, I'm thinking a disk 3cm in diameter, with 3mm black/clear marks at the perimeter. This could be attached directly to the threaded rod, rather than to the motor, and would have accuracy to about .01 mm for a 1mm pitch thread.
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