Re: [ATM] Equatorial platform

["Chuck Shaw" <cshaw@ghg.net>]

Geoff,

I have also built several platforms with roller drives (probably need to
take some pictures and post an article on this on my website, it needs
updating really badly anyway!).

There is no real problem in rewinding using the motor (one set of poles on a
simple multiple pole switch is used to change the direction signal to the
stepper driver chip, and another set of poles changes the R/C circuit to the
555 timer (assuming thats what you are using the generate the pulses to the
stepper driver chip) to a different set of resistors to drive things at a
high rate of speed.   A third set of poles can be used to turn the power off
to the system.

Using the output shaft should work just fine for the drive roller. You can
use the approach in the preceeding paragraph for re-wind, however, I found a
very easy way to rewind using a drive roller system that you might want to
also consider.   The idea is to introduce another roller under the sector
that is on a lever arm.  When you step on the lever, it lifts the roller up,
lifting the sector off the drive roller.   You manually push the platform to
the "reset" position, and then lower the sector back on to the drive roller
by lifting your foot off the lever.  Rewind takes about 10 seconds, the
drive motor never stops, and you are done!   You do not want to lift the
system off the drive roller more than what it takes to just barely clear the
drive roller.

If you want to do any imaging sometime in the future, a drive roller system
will probably give you better performance, but either approach can provide
performance good enough for imaging.

Enjoy!!

Chuck

Chuck Shaw
cshaw@ghg.net (home)
cshaw@ems.jsc.nasa.gov (work)
http://www.ghg.net/cshaw (S4: Stars, Sailing, Spaceflight & Stuff)



----- Original Message -----
> From: "Geoff Nelson" <gjnelson@absamail.co.za>
>
> If I am going to use a radial arm screw as recommended by Chuck Shaw
> on the atmsite. I will have a very low total gearing but also not be
> able to do a simple re-wind using the controller and reversing the
> motor and increasing the speed.
>
> So I looked at the option of using the shaft of the gear-box as a
> roller drive. Chuck indicates in his article that as long as you are
> above 20 steps per second then the vibration should not be
> objectionable in the eyepieces. I am on that limit. This option will
> allow me to automate the re-winding of the platform easily
>
> Now for the actual question. What have other people done to connect
> the roller to the 'cylindrical bearing'? Is it possible to use it as
> one of the support bearings rather than a separate drive entity? If
> you have done just this and have a website can you please send me a
> link so that I can have a good look at what you have done and copy it
> if it will work for me.



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