Motorising a Dob

[sharkbite]

Hi folks - after months of waiting for things to arrive in the post...
I have finally motorised my Dob.

The aim of this project was not to be able to do long tracking
or take DSO pictures, but track long enough to
keep a planet in a camera viewfinder for more than 5 seconds,
and have a bit more stability than bumping with my clumsy
mitts.

Purists might notice i only have one 30cm azimuth track (what a cheapskate) This was most definitely a money saving plan -
bearing in mind that this gives at least 4 hours of tracking.

Here is a basic parts list:

Altitude bits

1x 0.45rpm dayton motor (altitude motor)
1x 128t 32p aluminium hub mounted gear (1 inch bore)
1x 1inch hub mount for above
1x 48t 32p 1/2 inch bore aluminium gear
1x 3/8" hub mount for above to attach to motor


Azimuth bits:
1x 0.5 rpm gearmotor (azimuth motor)
1x 16t 32p 1/4" mount gear
1x 30cm 32p acetal gear rack.
Sundry metal items for mounting

Control
2x 12v PWM motor controllers for speed control
2x DPDT cetre off switches for direction control
Jiffy box to stuff it all in.

For mine, i think the altitude gear ratio is too low, so
it moves the scope too quickly - but 48t is the smallest
i could get to fit on the 3/8" motor shaft -if it is too
much of a problem some re-engineering will be required.

Here is a quick video showing the bits and how they work:

http://youtu.be/0V4lAv7nrsc

Shamelessly plagiarized from a video

by "Dakota Starry Nights" on youtube

Finished just in time to see the first cloudy nights in a month :-(

[White Rabbit]

Thats pretty cool, is there someway you could house the motor to muffle the sound as your neighbors are going to hate you at 02:00 in the morning.
I have my G11 run at less than half the speed to keep the noise down.

Thats a very cool mod though.

Cheers.

[sharkbite]

Thanks - i'm pretty happy with how easily it was done...

In truth the motors are not that noisy -
the azimuth motor can't be heard even at full speed,
and the altitude motor is only audible when slewing.
Your neighbours woiuld have to have extremely sensitive hearing
to hear it let alone be bothered....

You could use a quiter motor there, but since i use a sodding
heavy SLR for imaging, only the dayton has enough torque to
hold it.


Tried it out on saturday night when the seeing was terrible....
i am not brave enough to post the resultant Mars pic here yet,
but as far as the project is concerned my objective has been met!

Instead of having to edit down half an hours worth of .avi
to distill enough usable footage for stacking,
I managed to keep Mars in the camera viewfinder for 5 minutes straight before the clouds came and spoiled the party.

It is a bit harder to get the object in frame, but once there,
is is a snack to keep it there with the basic up/down and left/right
switches.

The altitude gearing is a tad fast, but not so much that
i am going change it.
Azimuth is bleedin perfect - once i had matched the sideways speed,
i only had to correct the altitude.

[Pinwheel (Doug)]

Great Idea, How much did it cost to build?

[sharkbite]

Thanks -

I spent around AUD$250 all up

($50 of which was postage)

[Pinwheel (Doug)]

Originally Posted by sharkbite

Thanks -

I spent around AUD$250 all up

($50 of which was postage)

Have you got plans & supplier parts list? I would like to make one too! I have an electronics background & can read Schematics.

[sharkbite]

Sorry i didn't work off, or create plans - i just loosely followed what "dakota starry nights did"....

I'm handier with a metal file than with a wood saw so all the
hard bits are aluminium.

I sourced all the gear parts from Little Bird Electronics in Hornsby (Servocity reseller)
Switches, boxes and connectors are from Jaycar.

The motor controllers are 12v PWM of which there are tons on ebay or dealextreme.com.

Sundry nuts, bolts and aluminium flat bar were in my shed,but
if pressed, i'd have got them from bunnings.

hope this helps - love to see someone elses take on it - so good luck!

cheers,

[Pinwheel (Doug)]

Could you post some photos on here please. Your YOUTUBE link doesn't show any real detail, also Photos could be printed out for workshop reference.

[sharkbite]

Sure - hope these have enough detail...
(i'd have to take it all apart to show more)

The dayton motor has 4 mounting bolts for which i cut
slots in the aluminium jiffy box so it slides up and down
(to engage/disengage gears)
It is held in the engagaged position by a bolt placed
in an appropriately postioned hole underneath the motor.

The azimuth motor was a lot simpler -
a single bolt holds it on a swing arm -
the motor is held up by friction,and you simply
push it down when you have the target in the sights of the
spotting scope.

As luck would have it - The GSO680 mount has a 1" diameter post - perfect for 1 1" hub mount for the large gear.
You do need to drill a hole to put a bolt through the hub - the hub cant grip the post tight enough to move the OTA. without it.

[Pinwheel (Doug)]

Great detail thanks, Now I can see what you did. Just a question but why didn't you use a pulley & belt instead of that large Alt gear combination. It would have been cheaper & easier to control the speed via a motor controller & potentiometer, not picking just wondering.

[sharkbite]

Cupla reasons...

Not sure if it would be cheaper or simpler to use pulleys....

The 2 gears + hubs cost all of AUD$40, straight off the shelf,
and fit to the scope like a bought one.

I have seen DIY pulley systems, but they all involved
having to make the large pulley yourself -

With the gears - there is no tedious mucking about with belts which can stretch and flex, creating wobble in the scope.

the "dakota starry nights" solution that i blatantly copied
seemed to be the easiest for me....

it is in fact being controlled by 2 motor controllers & potentiometers - i might go to computer control one day - but for now its good enough

cheers,

[Pinwheel (Doug)]

Thanks Sharkbite I'll take that on board.