weight distribution for eq6

[Gerry Casa Christiana]

Hello

Just a quick question about the weight distribution on a eq6. I have a SW 150pds and I have a situation where I am able to balance the scope using 1 or 2 weights. 

I noticed while setting up I can place one weight low on the weight bar and balance the scope or I can use two weights but move them both up close to the main bulkhead. Am I correct in thinking that 2 weights closer to the centre of gravity or higher up the pole is better than 1 weight? Or am I adding unnecessary weight to the mount. 

Thanks for your advice. 

Gerry

[glowingturnip]

have wondered the same, but since I leave mine built and physically lug my setup into position, i've gone for the one weight further out.

theoretically, I don't think it would make any difference, the torque the motor would have to put in is force x distance is the same in either case - but others might know better than me

[Gerry Casa Christiana]

34 minutes ago, glowingturnip said:

have wondered the same, but since I leave mine built and physically lug my setup into position, i've gone for the one weight further out.

theoretically, I don't think it would make any difference, the torque the motor would have to put in is force x distance is the same in either case - but others might know better than me

Yes I have heard that if for example you use the extension bar that it can cause vibration. I guess the real test would be a session of timing to see which way tracks for longer. I have a new setup so no auto guider yet so I'm not even sure what normal tracking time I can expect to get for a normal eq6. 

Its a interesting thought but I think the 2 weights would win in theory. I'll have to test it.

I will let you know. Unless it's possible to make a homemade Autoguider from a webcam?

[SkyBound]

I think this is a very interesting question....

And something I would like to know the answer to, 1 weight at a distance or 2 weights closer, hmmmmm

will watch with interest

 

[Uplooker]

I have always believed that it is best to have weights as close to the mount as possible as this reduces the overall moment of the balanced mount.

[Gerry Casa Christiana]

1 hour ago, Uplooker said:

I have always believed that it is best to have weights as close to the mount as possible as this reduces the overall moment of the balanced mount.

Yes I agree but the extra weight of 5kg may make a difference to motor strain? It's a interesting problem. I'm sure there is a Newton formula for this somewhere! 

[glowingturnip]

1 hour ago, Uplooker said:

I have always believed that it is best to have weights as close to the mount as possible as this reduces the overall moment of the balanced mount.

mm, don't think so - the moment of the system (the torque) is the weight multiplied by distance from the pivot, so 2 weights at half the distance is same as one weight at twice the distance.  But then if you have twice the weight on the mount, then you've got basically more stuff hanging off it, which can't be good ?  (the last bit is of course non-science hand-wavey)

[Gerry Casa Christiana]

http://www.engineeringtoolbox.com/levers-d_1304.html

After checking it looks like it's completely equal according to this so the only difference I guess is adding the extra weight to your equipment in which case it would be interesting to see if this creates extra stability for the mount or if this does in turn place more strain on the gears and the like. If the weather is good I'll try and test it 

[Uplooker]

42 minutes ago, glowingturnip said:

mm, don't think so - the moment of the system (the torque) is the weight multiplied by distance from the pivot, so 2 weights at half the distance is same as one weight at twice the distance.  But then if you have twice the weight on the mount, then you've got basically more stuff hanging off it, which can't be good ?  (the last bit is of course non-science hand-wavey)

I hear what you are saying, but the scope and weights/ mount are balanced, or should be, albeit ever so slightly heavy on west or east depending on which side you are imaging on. This is to keep the gears meshed.

[graemlourens]

The question is very valid.

For the motor there is no difference while tracking, whereby for slewing there will be a difference in the initial start of the movement if i'm not mistaken? If you're not over half the weight recommendations of the EQ6 then i don't see any problems.

The fact that indeed more weight is hanging from the mount is correct, but this can also be a benefit, making it sturdier and more resistant to external factors like wind etc.
Its a different fact if you're using the extension bar, as you'll for sure have flexure there that will be noticeable while guiding.

Kind regards, Graem

[souls33k3r]

1 hour ago, graemlourens said:

The question is very valid.

For the motor there is no difference while tracking, whereby for slewing there will be a difference in the initial start of the movement if i'm not mistaken? If you're not over half the weight recommendations of the EQ6 then i don't see any problems.

The fact that indeed more weight is hanging from the mount is correct, but this can also be a benefit, making it sturdier and more resistant to external factors like wind etc.
Its a different fact if you're using the extension bar, as you'll for sure have flexure there that will be noticeable while guiding.

Kind regards, Graem

So basically what you're saying is that using one counter weight and and the extension shaft/bar on the counter is extended will cause flexure? At the moment i'm only doing visuals so this is what i do, i extend the counter weight shaft/bar by using the extension rod with my NEQ6 pro mount and use only one weight. 

[barkis]

One advantage of using two weights,  is being able to keep bar more compact,  and therefore less protrusion.  Less chance in the dark of accidentally walking into it and knocking the scope off the target you are observing, /   imaging.    As long as you are well balanced,  I don't think it matters a great deal. A slight weight bias against the drive is usually preferred to keep any backlash at bay. 

[spaceboy]

For what it's worth I went with more weight and closer. For one I don't have to worry about bashing into an unusually long counterweight bar.

[graemlourens]

10 hours ago, souls33k3r said:

So basically what you're saying is that using one counter weight and and the extension shaft/bar on the counter is extended will cause flexure? At the moment i'm only doing visuals so this is what i do, i extend the counter weight shaft/bar by using the extension rod with my NEQ6 pro mount and use only one weight. 

I'd go for more weight and closer, yes. Its putting less strain on the counterweightbar and generally will be more compact. But i know from experience (with my AZEQ6 when i was going out in the field with it) that carrying 2 counterweights around is not fun, and for visual it will not make any difference any ways....

Kind regards, Graem

[Qftgr]

The angular moment of inertia is the (sum of the) product of mass times the square of the distance from the centre of mass of the system. So twice the mass half the distance in (giving the same pivoting force) is lower AMI. This affects only the reaction of the system to changing its orientation but not the balance. So several peoples intuition that more mass closer in is better is correct I think.

[DAVE AMENDALL]

Interesting one ! If one looks at the pictures of the really large EQs used on pro scopes it seems that multiple weights are used closer to the centre of gravity..................Dave

[Gerry Casa Christiana]

On 24/09/2016 at 12:28, DAVE AMENDALL said:

Interesting one ! If one looks at the pictures of the really large EQs used on pro scopes it seems that multiple weights are used closer to the centre of gravity..................Dave

Yes I think it's going to be a difference but marginal. When I get the clear skies I intend to test the inspiration I had. 

[glowingturnip]

On 24/09/2016 at 07:49, Qftgr said:

The angular moment of inertia is the (sum of the) product of mass times the square of the distance from the centre of mass of the system. So twice the mass half the distance in (giving the same pivoting force) is lower AMI. This affects only the reaction of the system to changing its orientation but not the balance. So several peoples intuition that more mass closer in is better is correct I think.

that is a very good point...  so for slewing when you have acceleration of the mount, more weight closer in is going to be better.

i'm going to stick with the one weight further out though, the rig is barely luggable as it is, and I can't be fussed with breaking it down

[Tiny Small]

On 24/09/2016 at 07:49, Qftgr said:

The angular moment of inertia is the (sum of the) product of mass times the square of the distance from the centre of mass of the system. So twice the mass half the distance in (giving the same pivoting force) is lower AMI. This affects only the reaction of the system to changing its orientation but not the balance. So several peoples intuition that more mass closer in is better is correct I think.

This may also have a noticeable and beneficial impact on guiding. Worth a test I think.

[Waldemar]

according to the laws of gravity and leverage it does not make any difference other then to bump in extended CW rods easier.

Besides that thin CW rods may bent, but that does not really matter. 

The distance from the point of leverage times the weight is the force to balance:  2 x 1 is the same as 1 x 2...

[laser_jock99]

I ran out of both bar length & weights.......

My prefered option though would be more mass, closer in. From a practical point of view it's less obtrusive - and I don't like banging my head on a 5kg counterweight in the dark that much either!

[Gerry Casa Christiana]

 

12 hours ago, laser_jock99 said:

I ran out of both bar length & weights.......

My prefered option though would be more mass, closer in. From a practical point of view it's less obtrusive - and I don't like banging my head on a 5kg counterweight in the dark that much either!

Looks superb! Doesn't look like a grab a go system though. Is that a 300 Newton?

or just 300kg! 

 

Gerry

 

http://www.engineeringtoolbox.com/levers-d_1304.html

After checking it looks like it's completely equal according to this so the only difference I guess is adding the extra weight to your equipment in which case it would be interesting to see if this creates extra stability for the mount or if this does in turn place more strain on the gears and the like. If the weather is good I'll try and test it 

[laser_jock99]

5 hours ago, Gerry Casa Christiana said:

 

Looks superb! Doesn't look like a grab a go system though. Is that a 300 Newton?

or just 300kg! 

 

Gerry

 

Gerry,

it's a GSO 12" F4 Newtonian. By the time I've added a guidescope & heavy DSLR it needs 35Kg of counterweights, which just about fit on the standard bar. The EQ6 copes very well- but as you say it's not portable!

[Linda]

I am sorry, but I didn't read all answers in detail. But I asked the question to my husband who is a physicyst. He says that 1 lower weight at the end of the bar gives a lower static momentum to the mount and therefore causes less strain than the double weight halfway the bar. It is the total amount of weight on the mount that matters. This is true for slow slewing. If spinning around quickly, the situation could be different.