Stepper motor question

[Bassnut (Fred)]

Just quietly, why arnt belt drives used stock on (any?) mounts these days?. Seem better, logical, and cheap, so..........

[kinetic (Steve)]

Originally Posted by aokman

has anyone taken into account the step rate of these motors also. At work we use types ranging from 3.6deg step down to 0.8deg step 3 phase with weighted dampeners and the driveline vibration is vastly better with a smaller step

im currently trying to incorporate one of these puppies as a focuser

I use 20 microsteps per step on the Bartels system but it is capable of
40.This is on a 400 step/rev stepper(0.8)
On siderial rate the steppers sing at a fairly high pitch, almost silently
if I have late night redneck AM radio on in the dome too.
I have to actually strain to hear it.
I have the Astrosyn stepper mounted on a round washer made from
a tube of neutral cure silicone sliced up into a thin 'rubber' mount.
I have experimented with 'rubber' flywheel couplings between the
motor and gearbox but a simple coupling of medical tubing works best.
High speed ramped slews are smooth as well. I can't really complain.
But all of this was done over years of refining.
The Bartels system will work 'out of the box' with default settings on
most stepper/ gearbox arrangements but it will need some settings
custom tweaked. Things like microstep spacings, motor currents, duty
cycles. All of this takes time. And patience. But it is well worth
persevering. Most of the criticism of this fabulous (free BTW) system
comes from people who haven't even tried the solution out.

Sorry for meandering OT!

Steve

[bojan]

Originally Posted by Bassnut

Just quietly, why arnt belt drives used stock on (any?) mounts these days?. Seem better, logical, and cheap, so..........

Well, timing belts are not cheap.. gears are cheaper.
Also it may be that it is simply "this thing is done this way" attitude..

In motor industry, timing belt is a norm today.
I remember when first cars with timing belts (instead of chain) appeared on the market: they were looked at with suspicion...

[aokman]

Originally Posted by alistairsam

Hi,

I salvaged a few steppers, helical gears from printers and fax machines after reading threads here, and wanted a control circuit for a 6 wire stepper.

one of these from a fax machine happens to have datasheets on the manufacturers website, and from that, its a 1.8deg stepper, 2A max, 50-850mNm torque. It has 6 wires. Not sure if it is unipolar or bipolar.
I've seen posts using the bartel system, but i don't want to use a laptop yet.

Just wanted to have three switches or options - slew, forward/reverse, track using micro stepping, and possibly micro stepping before tracking.

I've built a fork mount for my 8" Bintel Newtonian, so my prime objective is just tracking on the RA axis.

any suggestions, ideas?

would a servo be more appropriate if requirement is just tracking, or a PWM based speed controller for a normal DC motor.

I've seen the circuits from oatleyelectronics, but found this site to have better kits http://www.ozitronics.com/

i have been playing with a few lately ranging from a 0.8deg 1.5A 3 phase which i havn't had much luck with (yet) due ot the controller chip integration. Having more luck with the 3.6deg screw drive ones i have though you can just controll them through a parallel port if you wish, im assuming a 6 wire is a unipolar motor with 2 wires connected straight to supply.

Belt drive would certainly be interesting, like i said we use it at work but i would have thought the load of a mount with scope would cause a bit of stretching in the belt and maybe throw the alignment out ever so slightly...