Counterweight size

[peeceeTal2M]

I was wondering if there was a way to calculate the ideal weight of a counterweight needed for any given scope, i have a feeling that my counterweight is too heavy and would like to change to the lightest weight possible.

many thanks

Phill

[John]

Hi Phill,

I don't know a formula for it - it depends on the counterweight bar length I guess and that varies mount to mount. HEQ5 mounts tend to need more weight as their point of balance is different from EQ5's for example.

I found mine by hanging a plastic bag half way along the bar and filling it with things until it balanced the scope - I then weighed the bag !.

Very un-scientific but it did work

John

[Sam]

Phill,

You can, using a simple calculation. First measure the distance of the middle of you scope from the point of rotation (the middle of the dec axis) measure in metres (mine is 0.3m). Multiply 9.8 (acceleration due to gravity) times by the weight of your telescope (mines about 12kg) to give newtons (for me 117.6 Newtons) X this by the distance, mine is 35.28. Now to work out the counter weight we need to match this number. To make it simpler you could not bother with the 9.8 bit and just make sure the weight X distance on both side is the same (for me that's 3.6). So to work out how much weight I would need I would divide 3.6 by the length of the counterweight rod from the dec axis to where the middle of the weights act through (for mine that's 0.3 again). So I would need a counter weight of 3.6/0.3, surprise surprise equals 12kg. But I know I have only 10kg of weight so I need counterweight length of 3.6/10, 0.36 metres (hence why I have ordered a longer counterweight rod).

I hope that helps.

Sam

[MartinB]

Phil, not sure what is making you feel your counterweight is too heavy. Are you able to balance the scope in RA? If the answer is yes then, you don't really need to be over concerned. A heavy counterweight close up to the mount is much better than a lighter weight hanging off the end of the shaft. The counter weight isn't taken into account when considering the load capacity of the mount. I always load up close to the top of the shaft and have found this to be more stable when imaging in a breeze.

[John]

Phil might be aiming to keep the overall weight of the outfit down to make portability a little easier - my scopes have to be shifted around a lot so I can emphasise if that is his intention.

John

[cygnusx1]

All fine and dandy LB, how about when using a side by side plate with 2 scopes, camera, guide camera + accessories?

Had to make it harder for you eh?

Forget that, the calculation would be the same for the dec axis.

p.s One thing you forgot LB, the dec head weighs a fair bit(well for a heq5 so i assume the eq6 too ), that would need to be added into the equation.

p.p.s I've just had a further look at the setup - firstly the RA axis is irregular in weight distribution along the axis. So, the best thing to do, for an accurate balancing, would be to get the axis to balance w/out any equip on it. On my setup, i have a side by side plate too on top of the dec head. I need a 1.25kg weight just to get it to balance. Now do the calculation with the lever length x weight to work out your counterweight necessary.

[Sam]

Kevin,

Everyones setup is going to be different but the formula is the same (because it's just basic physics). I know for my setup I need a longer counter balance rod because I don't want to use another counterbalance weight. Working out what is required to balance cameras etc gets a little tricky because it's an asymmetric loading but still has a component along the longitudinal axis (not sure if I'm getting my Ra and Dec mixed up but you know what I mean).

The weight of the head is pretty significant, thanks for that, it certainly makes a difference.

cheers

Sam

[peeceeTal2M]

Thanks for the input guys, I'll have to dig out my calculator and start working the math out. The reason i asked was that the counterweight seems to be a homemade one and no matter where i put it the mount just doesn't "feel right". I've an EQ3-2 mount with a 10" f4.8 Europa on it and with this huge lump of a counterweight on as well I'm sure the mount is overloaded. Until i can afford an EQ6 I'll have to make do and want to try and reduce the overall weight on the mount if possible.

Merry Xmas

Phill

[MartinB]

When you say it doesn't feel right, do you mean it won't balance. The weight of counterweights isn't an issue if the RA is balanced. I have 17kg of counterweight on my mount up close to the top of the shaft when using a 10" LX200R. I can balance with 12.5kg at the end of the shaft but vibration suppression is worse with this lighter arrangement.

What scope are you using?

[peeceeTal2M]

I have a Orion Europa 10" f4.8, but the mount's only an EQ3-2 and with the heavy counterweight the slo -mo control's feel jerky and not at all smooth in their operation and when tracking the mount by hand the scope bounces....I'm no expert, but feel the mount is overloaded and would like to use the minimum weight counterweight even if it means using a longer counterbalance arm. The mount had been retrofitted with ds motors and an autostar but one of the motors had stripped a gear, leading me to believe that its overloaded.

Phill

[John]

....I'm no expert, but feel the mount is overloaded .....

I reckon you've hit the nail on the head there Phill - an EQ3-2 would be overloaded even with an 8 inch F5 scope :shock:

John

[beamer3.6m]

I reckon it is the OTA that is causing the problem, not the counterweight.

I think a 10" scope on the EQ3-2 is just too much for the mount.

[Tiny]

According to the Orion site the tube weight (only) on that scope is 10KG - Isn't the 3-2 good up to 7KG and after that...