Wednesday, 4 September 2013

Restringing - Part 1

Finally, I have started restringing my Armdroid....   It has not been without complications I can tell ya.....

The manual covers the stringing procedure (cable threading, pp 2-13 / 2-14), gives advise on the best order, some useful hints, and suggests threading is ideally done before bolting the arm into the shoulder - which eases access considerably:

Luckily... My arm is not currently installed in the shoulder in any case !

I decided it would also be good idea to remove the finger assembly, tension equalizer, and tape up any strings that might interfere with the new stringing.   I will start with the Wrist cables, before moving onto the Elbow, Fingers, and finally, Grip action cable.

But....  Trying to release the tension equalizer to release the fingers was a problem.... it wasn't coming out in a hurry, it was completely seized!

I couldn't get enough leverage on the retainer with my tools whilst still installed in the arm.  I had no option but to extract this component completely, and get the big guns (grippers) out on the case!

Couldn't quite make out from the blueprints how the finger cables are held in place - but after closer inspection discovered the cable is clamped by a pair of grub screws hidden inside the finger support on both sides:

The string pulled out after releasing these grub screws.

With the tension equalizer completely out and dissembled with Circlip pliers.  Liberally spraying WD-40 to penetrate, then with a pair of grippers wrapped by a cloth to protect the stub-axle, eventually the screw cracked...

I couldn't see any visible signs of corrosion, maybe it was glued in!

This picture shows how the tension equalizer is constructed:

And reassembly of the device:

The fingers are now completely removed from the arm, and will be strung later :

Remaining strings taped out of the way:

After final preparations, I was ready to start restringing the left hand side Wrist cable....  I made a number of false starts... what worked for me was starting at the very front, then working backwards....

I used everything possible to clamp the strings down to maintain tension as I worked the string through the next set of obstacles:

Next problem....  where had the tension spring gone?????

I then spent the next 1 2 hours searching my study looking for it... nowhere was it to be seen....  suddenly I spotted it... stuck to a reed switch magnet on the reduction gearing at the other end of the arm!  Having pulled it free, this was then installed as follows:

And eventually, persistence paid off....    SUCCESS

The excess string will be cut off during finally assembly & trimming

You can see the new Cable Camp being used here.  I still say, if you crimp it, your in for a world of hurt when it comes to tensioning.

 The string is looping around the drums and idle pulleys without any kinking or crossing itself....   Perfect!

I won't be surprised if the string needs some re-arrangement later, but basically, it's in place now and follows the blueprints exactly.   I am pretty happy with the result, but one thing is for sure....  You really need six hands, and four pairs of feet to do this !

Tomorrow, I will acquire a few extra 'bulldog clips' which should make life significantly easier when restringing the right hand side wrist.   If all goes well....  I might even make a start on the elbow cabling which on paper, looks a whole lot easier than the wrists!

If you've never done this before, like myself, then I would recommend buying a good pair of strong tweezers...  This is really fiddly stuff !