Date: 19-NOV-74  10:24 PM
From: Vic Scheinman (VDS @ SU-AI)
To:   waters @ MIT-AI
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 	BKPH sent me a printout of some of your arm problems.  I will try to respond to
 some of them
 1) You mention high joint friction.  This is most likely due to poor alignment of 
 the geartrains when someone other than I put the arm back together.  Or else, it
 may very well be that some of the brakes aren't working properly and are dragging
 some when they are unenergized.  Check to make sure that the power supply really turns
 the brakes off- even 1 volt is enough to engage the brakes enough to feel it.  If
 you do open the arm, look at the brakes, the disks should rotate freely, with no
 scraping when unenergized
 
 2) The stops on joints 1, 2,and 3 can be made wider, but this will reduce overall
 joint travel- I will also try to make the pots have a bit more range, so that 
 even if the arm goes off the pot scale, the wiper will read either zero or full,
 rather than open circuit (garbage).
 
 3) Broken gear theeth on joint 3.- where in which gear?- I made a machining
 mistake in the big output gear and the teeth are a bit thin at one spot, but
  this should be out of range.  I dont think you can rotate any of the gears to
 get broken teeth out of range- but check to see if the teeth are really broken 
 completly off.  I find that hard to believe on joint 3 unless something 
 or somebody did something to the gear. High friction in 3 is probably due to
 there being zero backlash in that joint- the gears are pressing together too
 hard.  Loosen some screws and wiggle things around a bit to try to put in a bit
 of free play.
 
 4) Joint 5- Check the motor, it should run smoothly when pure D.C. is applied.  You
 may have burned out an armature winding, but I doubt it.  
 
 5) Joint 6- Check the motor leads- try to run it on pure D.C. from an 
 external power supply- hooked up directly to the motor if possible.  On joint
 number 6 there are 4 brush terminals.  Make sure opposite terminals are wired
 together. (adjacent-90deg. apart terminals are opposite polarity). Does the joint
 turn freely when backdriven by hand?- try it, it not,the motor may be fine, just 
 a bad gear. Wen you tell me what is wrong, I may be able to send out a new
 output gear and pot with a better stop, if that will help.
 
 7)  See BKPH about my messages to him- they may help you out too.  
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Date: 19-NOV-74  10:23 PM
From: Vic Scheinman (VDS @ SU-AI)
To:   waters @ MIT-AI
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 	I hear you are having some problems with the arm
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