Re: Major Mark IV Problem

[Chris Albertson <chris@topdog.pas1.logicon.com>]

Tom Droege wrote:
> 
> Well, the Mark IV vibrates in RA due to the pulsed drive of the stepping
> motor.  I have done what I can with the magic gunk, and there is still too
> much vibration.  I see two ways to proceed.

How about a flywheel?  I would think that adding rotational inertia
would eliminate any pulsed rotation.  It would also mean that we'll
need to ramp the speed up and down carefully or risk skipping steps.
but the PC software can handle that.
You may also need a massive (five pounds of iron?) clamp on the motor.
You should be able to tune any residance way away from the step rate.

I'm thinking like an 1960's engineer at Cadilliac division of GM
"Given enough mass you can solve any problem"  Those old cars
would give you a boat-like smooth ride over any road.


> 
> My present plan is to switch to a synchronous motor for the RA drive.  This
> would get away from the 8/1 rewind to forward speed problem as I would
> expect to be able to drive a synchronous motor faster.  This will take an
> additional electronics card and testing, and ... and would take a few
> months.

If a redesign is required how about going to a system that uses
two moters coupled through a diferential.  Yes there is some
mechanical complexity but the control is simple. 1) The RA tracking
moter runs at the sederial rate or it is off.  That's it.  
2) The rewind moter runs flat out or it is off,  That's it.
The control is simple enough that you maybe can use the existing
STAMP board's extra control bits.

-- 
--Chris Albertson

  chris@topdog.logicon.com                Voice:  626-351-0089  X127
  Logicon RDA, Pasadena California          Fax:  626-351-0699