10" computerised dobs

[rikyuu]

hi All,

well, I've had a busy few nights. After my failed attempt at an equatorial platform for the Dobs, I bought a cheap Meade goto mount of ebay with the thought of computerising my Dobs. As the 10" OTA is 12Kg and the goto mount will support only about 4kg, I decided to build a Dobs style mount to take the main support of the scope, then integrate the goto into it to drive the ALT/AZ axis. One difficulty was the balance, the goto won't take too much imbalance on the alt drive, but with the finder scope and focuser on the top of the OTA, the centre of gravity shifts as it tilts. Fortunately, the new cradle it sits in adds some weight to the underside and balances out this quite well. I have to slide it slightly back for the heavy 2" lenses. It's gripped in the cradle by foam pads each side which will hold onto it to near vertical, but a couple of bungee straps around it makes sure.

Got my first chance to try it tonight, only had 30 mins though, but it seemed to perform quite well. The goto function was not entirely accurate, some grains of dirt on the platform bearings I think causing the Az clutch to slip, but once centred on Saturn, it stayed within the field of view for minutes at 187x mag, whereas before it would vanish in a few seconds. Plus when it did drift slightly off centre, it only required a short tap on the controller arrow buttons to bring it back to centre, without touching the scope, no vibrations, fantastic! Even at 375x mag, it still took about a minute to drift off, I'm so pleased, now I can look at my favourite planet as long as I want!! Time to try some DSOs too.

Here's a pic of my creation it's more function than form!

(click to enlarge)

[Astronut]

That's an intriguing (possibly unique?) and excellent mod. What a great idea

I'd like to do something like that myself but would have no idea how to go about it.

I take it the goto unit came complete with altitide and azimuth motors or did you have to get those separately?

[rikyuu]

Thanks, it was actually relatively simple, (sort of!), the mount was a DS2000 I think which included the controller and mount. The black arm unsrewed from the circular black basee and I extended the wires to the motor and sensor in the arm from the base. The other side of the a-frame is a couple of bearings on the alt axis, so the arm is only taking half the weight. The base of the mount simply rotates the frame on 4 bearings. It could probably be a bit neater as it's more of a working prototpye that had a few changes on the way, but it essentially works fine.

[G4AQB]

A wonderful piece of engineering!

Fred Dibnah would be proud of you!

I'm sure others would be keen to see plans of how it's done, especially as GoTo mounts can often be picked up cheap on ebay.

Steve

[rikyuu]

Thanks Steve, of course Fred's would have been steam powered!

Plans....ah erm, it sort of evolved! I'll try and describe it more detail when it's not so late

Cheers Lee

[GazOC]

Thats a very impressive piece of work!!