Off-Topic > Robotics

Things you've built/invented/programmed (or want to)

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MarvinMan:
This is a place to share and discuss your own hardware and software projects.

Feel free to post or ask about anything vaguely related, from your first attempts at controlling servos to building your own terminator army.

MarvinMan:
Here's a child size prosthetic hand I built for the group design project part of my degree.

The fingers can spread the load between all of the finger sections, and the two pairs of fingers can be independently driven. The fingers are actuated by a pair of screws directly driven by brushless motors, and the thumb is driven by a micro servo. We had a few problems with the screws sticking, but once it's moving it can grab things with a surprising amount of strength. It's meant to be controlled by an EMG sensor, but that stopped working a week before the final demonstration.

Almost all of the parts are hand machined, and the outer shell is moulded in fibreglass. I originally wanted to 3D print most of it, but the printers we have at uni are pretty poor quality despite being obscenely expensive.



z26:
That's pretty awesome.  Sucks about the 3d printers, tho.  You could always have gotten something from shapeways or the such, but I guess that would have been even more expensive than machining.  I'm curious, why did you went with fiberglass?  I must admit the rest of the hand looks much better relatively speaking.

I haven't done anything this cool (in fact not even sure these things qualify for this thread) but I have made a crude vacuum chamber (rather than buying the 150$ one from ebay)  Turns out Walmart do sell big, conveniently shaped vacuum proof jars at 30$, even with a convenient hole for the hose.  I agonized over a cheap yet stiff cover material (small pieces of thick cell cast acrylic aren't obtainable without costly shipping)  But finally went with a floor ceramic tile, since the jar is transparent anyway.  for the seal I cut some rubber mat thing that was made for chimneys.  The plumbing however was complicated.  Hose clamps were very useful, but I didn't have standarized parts so I had to fit a bunch of components not meant to join together.

In the end, it does work alright, which is very surprising.  Keeps reasonnable vacuum overnight.  With all the mistakes I made however, it cost me as much as a real one...  At least its pretty big.




Also, After I had to bring a plumber to defrost my water pipes (200$ a time) i ripped off the technique for myself with a tea boiler, a bucket, a hand pump meant to siphon gas (15$, wasn't going to wait a week without water for an electric one) and some silicon tubing.  While the pump did eventually fail, it did save me two calls, so this time I definitely saved money.

MarvinMan:
The fibreglass is mostly the result of not being able to draw something like that in solidworks. I had a few attempts at modelling it, but it was easier just to sculpt a form out of wax.

What do you use the vacuum chamber for? If you want to hold a vacuum for longer, greasing the sealing surfaces a bit should help.

z26:
The reason I wanted to make a vacuum chamber was for resin casting, which can make much stronger and lower tolerance parts than your typical 3d printer can.  This guide http://lcamtuf.coredump.cx/rstory/07-planetary-parts2.jpg is what gave me the taste of doing this.  With a good cnc mill you can do stuff like this.





Whats stopping me is that a decent cnc costs around 1500-3000$ and as you can see with my other post I'm strigny with money.  But maybe I'll do the leap one day...

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