Pan/Tilt Prototype is Complete

The pan/tilt hardware for my antenna tracking tripod is finished.  It even looks kinda like my design :D .

With the layer of zinc I didn’t account for, everything is actually pretty tight (after some sanding).  There is no play anywhere except for some slight backlash in the gears.  The mounting brackets don’t slide on the shaft and the chassis doesn’t rock on the main bearing at all.

The unit as a whole is pretty solid and weighs more than my scales will tell me.  My CAD software tells me it’s around 4 to 5 kg.

Unfortunately the small gears I received had the wrong bore size.  I couldn’t be bothered having new ones shipped from the US so I decided to drill them a bit larger myself.  This ended in fairly average results.  The gears fit the motor shaft fine, but they have a bit of a ‘wobble’ as they rotate which is less than ideal.  They’ll work for testing, but will be an issue when I put some load on them.  Some new gears from a local supplier are on the way.

The bends in the metal were off by a degree or two.  Not much, but the very tight tolerance on the shaft mounts mean that if the holes don’t line up then the shaft jams when I try to assemble it.  This was solved with my trusty sledge hammer, which was odd given the 0.05mm tolerance.

The electronics and their mounting are probably one aspect I put the least thought into.  I’m just using the Pololu A4988 controllers and mounting them in a very flimsy plastic frame.  It’s not my proudest moment, but will work for now.

I’d actually like to make my own board at some point.  The Pololu controllers are a bit pricey compared to the chip that actually does the work.  They also won’t easily accommodate a heatsink.  Without the heatsink I can only run the motors at about half their maximum power.  My own board would have actual mounting holes and a heatsink making the whole arrangement much neater.

The gears come with an M2 grub screw which is pretty small considering the load I’ll be putting on them.  These tiny screws need a 0.9mm hex key which is very small and not amongst my collection.  It also doesn’t appear in any sets I could find in the shops.

I had a go at tapping a new M3 hole for a bigger, more convenient grub screw.  This pretty much failed as the hole for a set screw is very shallow, and a hand-tapped thread tends to be crappy at the top.  So there wasn’t enough thread for the bigger grub screws.  I’ve decided to order the tiny hex key and see how the small screws go.

Right now I’ve mounted two SLA batteries on the chassis itself along with Asity as the controller.  This should let me play with it, without worrying about tangling cables.  I still haven’t written any software to control it, so no movement yet.

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