Friday, 7 March 2014

Drive Shaft Replacement

Today, I have been busy replacing the main drive shaft and reduction gearing....

I started by scavenging parts from the "donor" Armdroid....   I'm interested to see if the reduction gearing is in better condition than on my other Armdroid, so these were extracted, after removing the arm from the shoulder:


Nothing much left here now - motor pulleys have also now been removed for spare parts:


After a quick inspection, only two have hairline fractures, and none have splits extending to the edges, which is good news.  I'm going to use them all, but will swap those with hairline fractures to drive the wrist actions - this leaves the pulleys in absolute best condition to drive the shoulder and elbow joints.

I also made a last minute decision to reuse the drive shaft as this appeared in slightly better condition than my original.



The pulleys cleaned up very well - after trying various cleaning products, I found Lemon Cream Cleaner (what you use in your kitchen) worked best, and as an added bonus, they all smell rather nice!

After installing into my Armdroid, I thought it would be a good idea to perform another bench test, and see if this has made any difference to the performance.   Yes!  Things have certainly improved, and that "clunking" problem seems to have been solved.

When fitting belts, they should be placed fully on the motor spindle and worked gently onto the reduction gearing.

I also took the opportunity whist the arm is out of the shoulder to run plenty of WD-40 onto the drive shaft and started lubricating the spur gears for re-assembly of the arm.   Using my precision oiler, I managed to run plenty of oil onto the roller bearings and swung the entire arm assembly around 360 degrees to ensure everything was coated well.


Another thing was to pull on the motor end-floats and lightly lubricated around the pulleys and motor spindles.

Next, installing the interface board back into the base:


I soldered up a new power connector - not pictured, although you can see the chassis socket has been re-installed in the next photograph:


All motor channels plugged in following the suggest motor/function assignments:

CHANNEL
FUNCTION
1
GRIPPER
2
LEFT WRIST
3
RIGHT WRIST
4
FOREARM
5
SHOULDER
6
BASE

After bolting the base plate back in, one last bench test to verify all motor channels are still running.  It took some gentile persuasion to get the board along with all the wiring into position.


At this point - the base of the Armdroid is in super running condition.  Tomorrow, I will remounting the arm, possibly this might require re-stringing.   Once of the problems I've been suffering is an excessive tight spot on the shoulder & forearm joints.  I'm wondering if in my previous attempt to restring the arm, I over-tensioned some of the cables, and is causing too much friction.

Something else I recently noticed on my Armdroid, the finger terminating cable clamps are worn/damaged. This might actually be the reason why a string broke back in December.

I was curious how these fingers come to bits, but after trying with several different pairs of circlip pliers, I just can't find anything that fits these small circlips:


I popped down to a local Model Shop in Milton Keynes, and the guy in the store was also stumped as what to suggest.  So, I am on the lookout for an extremely high quality set of mini circlip pliers, and this job will just have to wait for another time.