a different dob drive system

BenK · #1 05-09-2007, 04:34 PM

Hey Mike,

Here are a couple of photos of the Eq platform I made recently..

In the plans a screw thread and tangent arm are suggested to drive the base, but with this set-up there is no slop at all, or tracking errors due to the arm being driven in a straight line.
and to re-position i just release the tension on the cable (like a guitar tensioner) and roll it back to the start position, then tension it again.

The cable goes once round a little roller, driven by a geared down DC motor.

It sure makes viewing more pleasant, with the full sectors it can track for around 90 mins.

I'd like to see what you reckon

Cheers,
Ben

bojan · #2 05-09-2007, 04:48 PM

Looks good...
The only potential problem may be a variable rotational speed of the DC motor... but then again, it can be controlled by tracking software or manually.. so it is not a problem :-)

joshman (Josh) · #3 05-09-2007, 04:53 PM

i like it, simple and effective

rmcpb (Rob) · #4 05-09-2007, 05:10 PM

Ben,

Does the cord go around the bearing or is it a straight pull?

Cheers

BenK · #5 05-09-2007, 06:37 PM

Hi Rob,

the cord is fixed to one side of the timber sector between the 2 aluminium ones under the dob base, then runs along its circumference, around the pulley/roller (seen on the motor assembly) and to the tensioner on the other side.

so it pulls around its circumference.

the base just rolls on 8 bearings seperate to the drive assembly.

I hope this makes sense...

Cheers

centauri · #6 07-09-2007, 10:55 AM

I wonder why people with dob trackers are not using a one way roller clutch in the drive systems, would make it dead easy to push it back to the start again.

bojan · #7 07-09-2007, 11:51 AM

Quote:

Originally Posted by centauri

I wonder why people with dob trackers are not using a one way roller clutch in the drive systems, would make it dead easy to push it back to the start again.

I guess because such a clutch would not move the telescope at all

What is needed is a clutch that can be dis-engaged... like the one used here..

OK, maybe it could have been done better, but it is not a problem to reset the whole thing once in an hour...
Maybe a friction clutch, that needs a certain force to start slipping is a better idea....