Tal-1m stepper drive

[markse68]

Hi, I just recently bought a Tal-1m on ebay after a strange urge to look at the moon and Jupiter again took hold of me- something I haven't done for years... My previous experience had been with a Tal 65mm newt I bought brand new back in the day from, I think, Telescope House- lovely little thing but this Tal-1 is something else!

I wanted a motorised equatorial mount as that was the thing that was a bit of a pain with the 65's alt-az mount and when I looked it was there waiting for me on ebay-  and I love it

The plan is to stick it in the boot of the car and drive off somewhere with a  bit better seeing than SE London so I wanted to convert it to battery power. Plus the synchronous motor drive was very noisy...and shaky- you had to turn it off if you wanted a clear sharp image

I opted for a stepper as I knew about these Trinamic drives with built in controllers and opted for one with "Stealthchop" which gives very smooth motion at low speeds. Bit pricey for a stepper but worked out quite neat and simple. You can programme in the speed you want it to run at and it will just start up and run at that speed as soon as it's powered.

It runs off a Makita battery pack through the original connector, draws about 250mA so should last for hours, and is very very quiet. I got my measurements a bit wrong I think when I was drawing up the 30:1 reduction gears so I have to mount it slightly off line to avoid the big worm gear clutch screws clipping the new brass gears but it works fine and tracks the moon well.

Mark

[sloz1664]

Hi Mark,

That's an excellent solution to the old Tal clock drive. I was always worried about the transformer to the original 12vac supply.

Steve

[Mick J]

Delightful piece of work,  so that's Makita to 12volts/5volts ?

[markse68]

Thanks Steve and Mick. I quite like the look of the old transformer as it goes 😉 but it’s not very portable- and that old clock drive was very noisy and shaky. I had to slacken off the worm a bit as it had a tight spot and I’ve limited the winding current to 200mA on the stepper to get it really silent, and it was stalling, but now it seems to be working excellently. I was using it last night for 3hrs(!) on the first clear night in what seems like ages with all the rain. Best nights viewing since I bought the scope- Jupiter, Saturn, Moon- so crisp and clear and the drive makes it so enjoyable 😊 Tried to split Antares and failed lol- think I might need more than 4” for that- though it did look different from other stars.

Dont know if it’s because they were all fairly low but they did drift a little- I can probably tweak the speed a little but it’s so much more stable an image than with it switched off I probably won’t bother.

Yes Mick- it’s meant to be a USB charger that you clip on your battery packs but makes a great little interface to other things with a simple drilled hole and soldered wires- I should fuse it really. They’re 10.8v (3cell ) packs so 12.6 fully charged and the stepper runs down to 8 or 9V I think.

Mark