Dec 24 2010

Robot eye tinkering II

Okay, so I’ve spent a little on the eye. I grabbed a £10 PS3 Eye while grabbing some other casting supplies for the business. And since whether the robot it’ll be attached to works out, I can still use it for webcasting from the workshop.

Also grabbed some M3 nuts; for some reason I have hundreds of M3 screws but no nuts.

Oh, and four flanged bearings. I don’t know the exact strength of these old servos, so didn’t want to make their job harder. For once I found prices cheaper than ebay. Most of the ebay flanged bearings were as pairs, so about £2.50 each for ones with a 3mm ID. Fast Lad Performance did a set of four for £4.08 (£6.45 inc signed postage).

The bearings arrived the other day along with some of the plain (not nyloc) nuts.

While I was waiting for them, I managed to do some repair-soldering on three of the servos with cut-short wires.

This is the sort of thing. Wires under an inch long from the PCB. I cannibalised the cables from some PC case-fans since they already had 3-wire cables with connectors on them at a standard 0.1″ pin spacing. Handily the wires are also the same colours as the servo ones!

Had to trim back the rubber gland a bit on one so the wire could bend sharply enough to clear the mechanism.

Why are the wires always at the end with the mechanical output too? It seems to mean robotics using standard servos end up using oversized brackets to clear the cables.

I also cut up the small servo with broken gearbox and got the potentiometer hooked up to a gear after a lot of trial, error and fusing gear & hubs together with the soldering iron.

When the cross-piece was cut down a bit I also drilled holes and bolted the pot-end to it, and then added the other half of the servo carcass to the conveniently identical-sized focus motor. Means I’ve been able to hide the servo’s PCB in that half for safe-keeping. Nice & tidy.

With the new bearings I drilled out some slices of the old shower cabinet frame and used them as brackets to mount one of the servos. The join is a bit loose because I over-filed the square hole, but it’ll do for the rough version.

I pressed the cowling on and loaded some nuts into it for weight. Weighing them after it drooped, I’ve got another 80grams before the servo gears won’t hold it locked in position it seems. I might be able to get away with that just fine, but it may mean bigger servos if I add an auto-focus mechanism later.

I then grabbed the tin-snips and made up a small mount for one of the small speakers from an old laptop. It looked okay, but I quickly realised it would foul the pan-tilt mechanism. I’ll have to go inside the cowling somewhere.

Need to fab up the pan mount next. Trying to get some weight away from the arms end I’m going to try and run it from a servo near the elbow using some old printer toothed-belt if I can find a matched set of belt gears.

I can probably clear up some of the tinier parts now and make some space again now the basics are together. It should get bigger & cruder as it goes down toward the base. Got some old printer flanged-bearings for the elbox & shoulder (8mm ID).

It’s enjoyable so far. But I really want that cheap camera to arrive. I know xmas post slows things down a lot, but I am a little concerned.

Please excuse the photo quality. These ones were grabbed quickly with the mobile phone. There’s enough loose glass-fibre in the workshop at the moment I’m loathed to take the good camera down there.

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