Tal 2 mount DEC bearing overhaul- please help

[CraigT82]

Nice work Mark! Looking forward to seeing the end result (if there is such a thing for the modding enthusiast 😉). 

Are you building a mount from scratch now? Based on the harmonic drives?

[markse68]

Thanks Craig  That’s my plan but it could take some time. I think a motorised dec is pretty essential for long exposures and whilst I like the Tal, it’d be a real bodge to motorise it. 

It’s filling me with excitement and an equal amount of dread at the moment- there’s a lot of bits of aluminium to design and machine and the costs involved in that and then there’s the interfacing it to a pc which i know nothing about and it’s all so confusing. But i work with v clever programmers so i’m hoping i can convince one or two of them to help me out with it if i need it. 

Harmonic drives are great but not really ideal for the accurate motion we need but the PE tends to be low frequency and predictable so I’m hoping it’ll work ok- there’s a few commercial mounts out there that seem to work ok anyway. The nice thing is the freedom from backlash

Mark

[CraigT82]

Sounds exciting! Might be worth exploring if you could build it around the brains of an existing model? Motherboards from EQ6s are pretty easy to come by, though not sure if you could control harmonic drives with one of them. 

Just thinking that way it would then be really easy to control it via ascom using SGpro/NINA/APT or whatever.

[markse68]

Yes that’s a great idea- I’ve been trying to get my head around Onstep and others- i definitely need it to be Ascom compliant either by emulating another existing mount or whatever. Right now though i need to figure out how and if i can drive them at all- the built in motors are AC servos designed for 50-100V but i’m hoping they’ll have enough torque with just 24V DC. I think it should be ok- I don’t need much speed after all. They came with ac resolvers which i can’t use so I’ve picked up some encoders that i need to fit. Lots of fun

Mark

[Retro]

On 28/06/2019 at 22:24, markse68 said:

I know this isn’t very interesting to most but I couldn’t find this info anywhere so maybe it’ll be of use to someone down the line.

Made progress today- I made a spanner for the upper bearing housing using the heads of 2 m4 Allen screws to engage the notches in the housing.

Alas I still couldn’t unscrew it...

This part had me beat and couldn’t undo threaded collar 😔

[markse68]

19 hours ago, Retro said:

This part had me beat and couldn’t undo threaded collar 😔

Hi Retro, did you remove the threaded part from the other end of the shaft first- the part that the weight bar screws onto, and the little locking grub screws? I got that bit really wrong at first. Maybe warming the housing up a bit with a blow torch would help?

Mark

[Retro]

Yes Mark everything went great apart from that but all is good now, all back together, apart from a little play in ra axis, might need nipping up a tad more

Cheers