Wednesday, August 18, 2010

Poor Man's SkySensor 2000 Re-Engineered

Lalai and I went to Punggai, Malaysia, last 7th - 9th August, with the SingAstro folks. The first day was a bust due to clouds, but the second day was quite OK. I just had a lot of problems with my Vixen Great Polaris with Autostar refit. The most annoying was the tendency of the Oldham couplers to slip, which caused loss of tracking. But the killer bug was the C9.25 OTA colliding with the motor bracket when pointed at Lyra (basically to the North-East, above a certain altitude).

Also, the Autostar hand pad was very unresponsive due to the well-documented wearing-out of the rubber keypad. These problems really got me thinking that I should be buying a Takahashi mount. Sure it's lots of money, but leisure time is valuable too and wasted doing field repairs. I guess I am a bit lucky; one of the folks who went to Punggai couldn't get his new Meade LS-6 working.

To avoid the mount collisions, I had to re-fabricate the brackets so that the motor doesn't stick out where the OTA can hit it. To do this, I had to use some pulleys. The problem with such a scheme is that the Meade DS motor shafts are not held in place by anything, they rely on being mounted straight-through to the couplers.

I found these "rod end bearings" from RS Online, which I'm using to fix the end of the motor shaft:

I used a 6mm bolt (with the head cut off) as replacement motor shaft. From left to right, the rod end bearing (self-aligning); timing belt pulley with two set-screws; and the Meade plastic gear.

Here's what it looks like on the motor:

I fabricated some new aluminum brackets for the motors, and screwed these brackets to plywood scrap.

Close-up of the RA axis:

and the DEC axis:

It ended up really easy to mount the rod end bearing to the aluminum plate, as the bearing had an M6 bolt as part of it; a simple wing-nut held it in place.