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My new drills have arrived and I’ve now drilled all the holes for the RA motor mount. It looks a bit like a Swiss cheese. This is the “outside” face, with holes for the motor flange, the four mounting screws, the RJ11 socket for the motor cable, one for a cable tie to keep the wiring neat and an access hole for fitting the motor mount to the telescope mount.

The face that fits against the mount has access holes for reaching the motor mounting screws and a large one to make sure there is clearance for the pulley.

In fact, having fitted the motor I didn’t actually need the clearance hole, though there’s not a huge amount of space between the face of the pulley and the aluminium channel.

I filed a flat on the end of the motor output shaft for the pulley grub screw to bear on, fitted the pulley and drew the wires through some heat-shrink (as yet unshrunk) to keep them neat.

The last step for this motor is to solder the motor wires to the RJ11 socket, after which the entire unit can be fitted to back to the mount.

My pulleys and drive belts arrived today.

I removed the grub screws and drilled out the 48-tooth pulleys to 6mm (from 5mm) in the lathe to fit the worm spindles and the 16-tooth pulleys to 5mm (from 3mm) to fit the stepper motors. I chose to use the lathe rather than the pillar drill purely to give me a better chance of keeping the bores central. Unfortunately that’s pretty much all I can do for now, though the stepper motor spindles don’t have a flat so I may need to grind one for the grub screw to bear on if it doesn’t work without.

I need to cut a 22mm hole in the mounting brackets for the motor body to sit in, but that will be much easier to do with a 22mm drill in the pillar drill rather than trying to centre an oddly-shaped piece of material in the lathe, taking it out to about 18mm with a drill and then boring the hole out the rest of the way.

I don’t have a 22mm drill bit at the moment, but one is on order. As soon as I have that I can get on with cutting those holes, drilling the mounting brackets for the motor mounting screws and assembling all the parts. After that I think it’s just cabling that will be left.

I ordered some aluminium channel (1″x2″x1/8″) to make up the RA motor mount which arrived yesterday. I chose this size because there’s only one mounting hole for each of the normal aftermarket motors on the EQ3-2 and this would give me a reasonable spacing between the pulleys whilst allowing one edge to be flush with the back edge of the RA gear housing so that even with just one bolt holding it in place the mount won’t turn. I cut the metal to fit and drilled a hole to take the bolt in the back, matching up with a larger access hole in the front.

The DEC motor mount is a piece of 2″x2″x3/16″ aluminium angle that I found lying about in the workshop.  That I cut so it could use the existing motor mounting lug, but again fit flush against the mount body to prevent it turning.  I’ve not drilled it to fit yet however, as I want to see how the pulleys will line up first.  Once I know where everything is going to fit I might well cut it down so it isn’t quite as bulky.  Here you can see the RA mount in place with the DEC just resting where it will eventually go:

With the RA mount in place I could work out what sort of spacing I’d have for the pulleys and therefore what sizes I could use.  I’m going to use MXL belts and was tempted to go for a 12 tooth pulley driving a 48 tooth to give a nice round 4:1 reduction, but the 12 tooth pulley would need drilling out a little to fit the motor spindle.  As doing so would leave very little meat on the pulley boss, I instead opted for a 16 tooth pulley and a 3:1 reduction ratio.  With a 75 tooth belt that gives me 42mm spacing between centres which works out nicely.  I’ve ordered the belts and pulleys and will cut the holes for the motors once they arrive and I can check exact spacings.

I’m thinking that I might need to cut away some of the back face of the channel for the RA motor mount to give a bit more room for the pulleys and belt, but I’ll see how things work out once they arrive.