Sunday, 15 September 2013

Motor Pulleys - Upper & Fore arm

Today, we're heading back into the workshop to modify the stock 14T pulleys to replace the broken ones on my Armdroid.

These motor pulleys are located at the front of the shoulder assembly and are used to operate the Upper and Fore arm functions.


First problem was how to reduce the overall length, and hold this tightly in the Lathe to perform necessary machining without damaging the pulley:

Original
New - slightly longer which will cause alignment problems without modification

....and this picture shows how we got around that problem


We temporarily bolted the motor pulley onto a 40mm cap-head bolt and secured with a Nyloc.  This allows the workpiece to be installed into the lathe without damaging the pulley flanges.



We also carefully checked the center alignment with a steel rod - necessary for boring out to accept the motor spindles.

After this we started machining away the excess length.  This resulted in a small section which could not be easily machined, but that could be drilled out later!


Now for drilling (after removing the temporary bolt)...


We was a little cautious, and did this in small increments, starting with a 3.8mm drill bit, followed by 3.9mm, and finally 4.0mm.  I wanted these pulleys to be tight fitting onto the motor, and tight is exactly what we got!

Drilling pilot holes for the grub screws:


The mincraft drill is not really suitable for this kind of work, but with a little perseverance and patience we got there!

Finally, tapping both holes to accept M3 grub screws:


This procedure was repeat to make two complete pulley replacements:


Still need a little tidying up, but they are exactly the same as the originals, and almost ready for installation.