Dob OTA counterweights

[Astronut]

I need one or two counterweights to balance my dob's OTA altitude movement. When I've got a big train of eyepiece, powermate and paracorr in the focuser, the altitude movement is out of balance and the tube slowly tips downwards below 40-45 degrees. Tightening the altitude tension to compensate kinda defeats the objective of smooth altitude movement.

A couple of easily removable and positionable magnetic weights attached to the top of the tube at the mirror end would be ideal. I read somewhere one solution is speaker magnets wrapped in felt (to prevent scratching) but where the hell do I get speaker magnets from?

Just wondering what solutions people are using with their dobs. Material sources would be helpful too.

[ringz]

Hi Astronut.

I've heard of people making bags of lead shot or marbles, something fairly dense, and using velcro to attach them to the OTA.

Thats a nice cheap thing to try

Regards,

Martyn.

[Doc]

Maplins sell speaker magnets.

[Astronut]

Thanks I'll have a look at Maplins. I'd rather have magnetic weights than velcro attached ones.

[Andrew*]

Maplins sell speaker magnets.

link?

Andrew

[Andrew*]

Is there anywhere one could get dud speakers? They would cost next to nothing...

This is one idea here - stick them to something nice and heavy (up to 0.9kg) and you have up to 4.5kg counterweights, as you need them!

Then there's superglue and ordinary magnets...

Andrew

[Wobbly Bob]

Hi Ian, Wobbly Bob here, Car Boot Sale's, thats where I get all my junk from. Good luck

[TheThing]

Is there anywhere one could get dud speakers? They would cost next to nothing...

Try freecycle.org. People in my area are always giving away speakers.

[Milamber]

I used to use one of those weighted exercise arm/wrist bands on the 22" if weight was needed - just wrapped it around one of the truss tubes. To fine-tune simply slide it up or down.

Arthur

[Astronut]

These look ideal:

http://paceweights.com/

...only available in USA though but I could order some online if there's nothing else I can find.

or these:

http://www.shapeupshop.com/fitness/dumbbells/plate_mate.htm

Has anyone seen anything similar available from a UK dealer?

[Andrew*]

This was my solution.

Milk carton + 2kg sand + magnets + sellotape =

(click to enlarge)

Add one 16" dob and some felt to avoid scratching the lovely paintwork, and you get:

(click to enlarge)

Price: £3.49 + pennies

Result: one adjustable dobsonian counterweight

I don't recommend using felt, though. It makes it slide down the tube (but still works perfectly up to an altitude of about 50°). Use something with a bit more friction, but still very strong, so that the magnets don't scratch the OTA. The magnets are VERY strong. Gaffer tape would do the trick.

Andrew

[Astronut]

That's brilliant

I was looking around the house today for something suitably compact and heavy to temporarily strap to the tube. I've worked out I need around 4lbs of counterweighting.

I've got loads of empty milk bottles ready for recycling but it never crossed my mind that one would come in handy as a weight. Good thinking Andrew :salute:

I don't use evil-bay so I might get some of those self-adhesive magnets you linked above.