Fixing a hobbled droid

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Fixing a hobbled droid

The past year, I’ve taken R2 out on various outings and had lots of fun.

However, I’ve made the biggest mistake of them all.

“If it ain’t broken, don’t fix it!”

I had a working drive train with R2 using scooter motors, but I wanted to change into a better drive system that uses up less power and weighed a lot less than the old system.

I opted for using Jaycar motors, and found a wheel with a hub that was made for mounting directly on the the drive shaft. Only problem: it had another dimaneter than the drive shaft on the actual motor.

Not a big issue, I found a piece of fitting aluminium pipe and cut that off to the correct dimensions and all is well.. or so I thought.

On the first real outing, I encountered a piece of thick, sticky carpet, the worst kind of surface to drive on –ever! Half an hour into the event, He stopped moving. HE. STOPPED. MOVING! .. Panic!

So what it turned out to be, was that the small grub screw that locked the hub on to the ankle had slightly loosened, and the entire hub (with wheel) was just spinning loosely around the shaft.

So, I had to do something about this. I worked on another system, based from fellow UK R2 Builder, James Short, using two drive motors in each foot, hoping that the added torque (and better fit with better wheels) would prove better and fix the issue.

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Well … it was better, but it did not fix the problem.

The grub screw still comes lose and skids around the shaft, damaging it, and makes R2 immovable. This time we had two wheels on each side so it is a lot better but not good.

This is what the shaft looks like after a short while. Note the damage on the left side. The dent is due to the grub screw slipping.

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Removing the hubs from the shafts turned out to be quite difficult. I had to oil up the shafts and start the motors running at full speed, while trying to pry and slip the wheels off.

I asked around for various solutions, and fellow R2 Builder and good friend Sigge, checked with a few people at work, and basically came back with the best option: To drill a small hole (not through) into the drive shaft, so the grub screw would have somewhere to really stick, and seal the position of the grub screw with a thread locker, such as Loctite 272, the hardest out there.

Drilling a hole in to the shaft turned a bit easier than I thought, possibly due to me just byuing hardened steel drills that were up to the challenged. I started with a 1,5 mm hole, went up to 2,5 mm on the second time, and finally settled in a 3,2 mm hole. The hole itself is about 1,5 mm deep into the shaft, so just deep enough to allow the grub screw to take hold.

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Not bad for being done freehand without a pillar drill!

I am awaiting new wheel hubs, since they old one did not get through the removal process untainted, and the thread locker. Once that has arrived (should be next week) , the wheels will be assembled again, and hopefully it will all work out as intended!

My last option, is to drill down through the hubs and shaft all the way through and insert a steel pin, but that will severely weaken the shaft… but if worst comes to worst, that is the last option! =)

So, for now, this is the situation. Next up: time to rewire the electronics in the dome and mount those servos!

By | 2016-12-06T00:00:29+00:00 January 5th, 2014|R2-D2|Comments Off on Fixing a hobbled droid

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