a question of weight/balancing

[RT65CB-SWL]

I have 2x 1.9kg weights for when I attach my ETX105 & C6 on a side-by-side configuration on my Vixen GP.

I have treated myself to a 'used' Nikon D80 (with a low shutter count) plus a Nikkor 18-55mm lens & wired shutter release on 'Black Friday'. I want to attach the DSLR to one 'scope and maybe a digital compact camera to the other.

My heaviest e/p to date is the TeleVue 13mm Nagler T1 ...maybe OTT on the ETX105 ...but looks wonderful on the C6. Then I add my Crayford focusser and 2" star diagonal... more weight added.

Is 3.8kg enough?   I know balancing is important and can lead to some minor issues if not done when 'scopes are mounted side-by-side.

[Tomatobro]

My personal preference is to not add more weight but have an extension made to the shaft so that the same weights can be moved further out. A machine shop can make you one if they are not available for your scope. 150 mm is usually enough.

Brass is a good material to have it made from. One end needs to be threaded to screw into the safety screw hole the other threaded to take the safety screw

[Ibbo!]

I would add the weight as it closer in to the mount and will give less problems with settling time

 

[LightBucket]

Yes, add more weight closer to the mount, moving the weight farther out will move the centre of gravity and cause more strain on the motors, its been proven that on an equatorial mount its better to add more weight and have it as close to the mount head as possible..

[Stargazer33]

+1 for more weight closer in. I wouldn't trust the small thread diameter on the safety screw to hold four kilos!

[RT65CB-SWL]

18 hours ago, Ibbo! said:

I would add the weight as it closer in to the mount and will give less problems with settling time

 

 

17 hours ago, LightBucket said:

Yes, add more weight closer to the mount, moving the weight farther out will move the centre of gravity and cause more strain on the motors, its been proven that on an equatorial mount its better to add more weight and have it as close to the mount head as possible..

 

17 hours ago, Stargazer33 said:

+1 for more weight closer in. I wouldn't trust the small thread diameter on the safety screw to hold four kilos!

Thank you so much guys! ...these were my thoughts too! 

@LightBucketMy Vixen GP is still 'manual' ...but I will bear that in mind should I decide to add a drive or drives to it at a later date.

 

 

18 hours ago, Tomatobro said:

My personal preference is to not add more weight but have an extension made to the shaft so that the same weights can be moved further out. A machine shop can make you one if they are not available for your scope. 150 mm is usually enough.

Brass is a good material to have it made from. One end needs to be threaded to screw into the safety screw hole the other threaded to take the safety screw

@TomatobroWith the dec weight being further out from the mount, would the dec shaft flex a little bit and cause vibration? 

[Tomatobro]

 

Lets say we have a scope+ equipment that weighs 8 kg and when mounted its C of G is 200 mm from the RA axis

8 x 200 = 1600 mm/kg

So our 3.5 kg balance weights have to be 1600/3.5 = 457mm from the RA Axis  Total weight on mount head 11.5kg

But to balance with (say) 5 kg of weight 1600/5 = 320 mm from RA axis (more weight closer in) Total weight on head now 13 kg (13% more)

In engineering there is a saying "myths get repeated so often they take on the status of fact"

 

 

[LightBucket]

19 minutes ago, Tomatobro said:

 

Lets say we have a scope+ equipment that weighs 8 kg and when mounted its C of G is 200 mm from the RA axis

8 x 200 = 1600 mm/kg

So our 3.5 kg balance weights have to be 1600/3.5 = 457mm from the RA Axis  Total weight on mount head 11.5kg

But to balance with (say) 5 kg of weight 1600/5 = 320 mm from RA axis (more weight closer in) Total weight on head now 13 kg (13% more)

In engineering there is a saying "myths get repeated so often they take on the status of fact"

 

 

I understand all this, but what are you saying... you should have more weight closer or not..??

[John]

Having tried both the extended CW bar approach and more weight closer to the centre of gravity of the mount I'd definitely prefer the latter approach to minimise overall vibration. I've found this with the HEQ5 and EQ6 mounts.

 

[Tomatobro]

Reading the original topic the concern  was that we have a mount which has limited load capacity and the owner was concerned that with all the equipment he wanted to add the weights with the mount would not be enough at full extension to balance out.

The balance weights and balance weight shaft length are designed to match the weight capacity of the head.

I think that the lad was asking (under these circumstances) is it ok to add more weight to balance the assembly even though its at its limit. Under these circumstances moving the existing weights further out is far better than adding more net weight. It has to be a better compromise than what is being suggested?

If the mount is well within its rating then adding more counterweight is usually the lowest cost way of achieving the goal.

[LightBucket]

52 minutes ago, Tomatobro said:

Reading the original topic the concern  was that we have a mount which has limited load capacity and the owner was concerned that with all the equipment he wanted to add the weights with the mount would not be enough at full extension to balance out.

The balance weights and balance weight shaft length are designed to match the weight capacity of the head.

I think that the lad was asking (under these circumstances) is it ok to add more weight to balance the assembly even though its at its limit. Under these circumstances moving the existing weights further out is far better than adding more net weight. It has to be a better compromise than what is being suggested?

If the mount is well within its rating then adding more counterweight is usually the lowest cost way of achieving the goal.

Actually no, that is not always better.. sorry to disagree, but in this case with no motors being used then i suppose it wont make much difference