Keep your friends close but your weights closer?

[vlaiv]

Recently, I completed list of equipment (almost, it's always sort of never ending, isn't it? I mean the "needed" equipment list) that will enable me to to get more imaging time out of time under the stars.

My setup is now as follows: RC8" + TS80 photoline, side by side on HEQ5 (with matching cameras, covering about same TFOV and having roughly matching resolutions, one for Lum, other for Color).

I'm aware that I am pushing it a bit in weight department (13kg mark, or there about with all the gear mounted - RC being 7.5kg, Apo around 3kg, and all the bits and pieces will add to 13kg, maybe even 13kg+). 

So I ran into balancing issue, 2x5kg just won't do. First I decided to get extension bar only to later find out it is not such a good idea. I turns out that more weight closer to pivot is better than less weight further away. Balance will be the same, but angular momentum depends on square of the distance - so in later case there will be higher load on motors and guide responsiveness will be worse (also RA oscillation and host of other things). Ok, no problem, I'll just do 3x5kg - I have extra 5kg weight that I used to stabilize the mount (it was "mounted" on legs spreader piece), but this got me thinking - what is the best "distribution" of weights on the shaft?

There are numerous ways that one can position 3 weights to balance out setup, 2-1, 1-2, 3 just to name few of them (2 weights next to each other with one being further, first one then group of two further down, or bunch all three together and move them together to find balance point). So which combination is the best in terms of giving the least angular momentum to the weights system? My gut feeling was that it had to be group of 3 weights next to each other (probably worst case for balancing because one needs to move them in group to find the proper balance), but I had no solid numbers to back this up, so I created a simple spread sheet to do basic calculation of these three cases mentioned (proper analysis would require a proper algorithm and computer program to find optimum solution, and indeed it is quite an interesting "competition" level problem for those who are interested). And indeed, after I ran the numbers it turned out that group of 3 has the least angular momentum in weights system (3 < 1+2 < 2+1), so for the time being, until proven otherwise - conclusion stands - keep your weights together when balancing.

[AKB]

Yes.  Anything other than touching will move the COG of the combined weight further outwards, hence also the moment of inertia will be higher.  I actually chose an extension arm in a similar situation, though, because I felt that 5 kg less weight on the mount was probably better than more weight and a slightly lower inertia.

The problem becomes slightly more interesting if the weights are not equal, but still not hard to calculate.

[iapa]

I saw a video on Youtube the other day which discussed this subject.

Not sure how helpful it will be to you.

 

 

 

[LightBucket]

Very interesting video