Saturday, 20 July 2013


I started stripping the arm down this morning...  After reading the construction instructions a couple of times and plucking up some courage, I eventually unfastened the two bolts holding the arm onto the shoulder...

...and the forearm & upper arm assembly came out surprisingly easy

The shoulder assembly itself was really dirty and greasy, so I started to swab where possible...

...but soon discovered cleaning wasn't going to be possible unless the shoulder side plates are removed... so having decided this, next job was figuring out how to release the reed switches and spacers without loosing everything in the process:

Removing the sensors wasn't such a problem, removing the main drive gearing however was a major hassle... One of the bolts had rusted slightly causing the axle to seize.  It took a number of attempts, and a lot of shouting, and swearing to work things free!

With the sensors, timing belts and drive gearing out of the way, the side plates came out without any further problems:

I also removed all the remaining pulleys from the steppers, the hand motor and it's supporting bracket:

Ah!  Much better now...  Nice and clean!

But... and this is a real big BUT

When I was looking at the main drive gearing I noticed the large pulleys are split, and it wont take much before these guys start failing apart:

You can see the hair line crack in the pulley in the picture above ^^^

What's really worrying, is that all of the reduction gears have failed in this way:

This looks to be real week point in the design.  I'm pretty convinced the base gearing will also be suffering with the same issue.

The sprockets appear standard stock, as too with the 72 teeth single flange pulleys, but they've been pressed together with a little machining.  If anybody out there used to work for Colne Robotics, and can let me know exactly how these parts were fabricated, that would be fantastic... Otherwise, I'm going to have to measure everything up, and call Davall Gears once again!

Next job will involve taking a look inside the base...