EQ mount design query

[Tommohawk]

Hi all. 

As part of my ongoing musing/dithering regarding a more portable set up, I've been looking at ways to reduce the dependence on counterweight mass. One thought in particular crosses my mind.

The counterweight obviously have to balance the weight of the scope/finder/camera etc, and this could be reduced if the scope were closer to the RA rotational axis. Currently my HEQ5 + SW200 has a C of G about 300mm above the axis. So if the bar length is say 300mm (its a bit longer I think) then the CW weight would have to equal the scope + bits ie ~10kg. 

The dec drive and clutch is mounted at the top of the mount unit, just under the puck. But why dont they fit the drive and clutch underneath on the counterweight side? This would bring the scope closer to the axis by approx 75 mm and reduce the CW mass by errr...... gropes for calculator.... quite a bit. 25%?

I cant see why this wouldnt work - yet all the brands seem the same.

Any thoughts?

 

[andrew s]

I think it is best mechanically to have the main load (the scope) as close to the top bearing and point of drive as possible. This increases the torsional stiffness of the drive. Indeed on the Paramount the top bearing and worm drive are integrated together.

Regards Andrew

[ollypenrice]

One portable rig one idea that came up at our dinner table was to use the battery as the counterweight. I think one firm has started doing this now? I also think you're right that optimizing the position of the saddle plate from a C of G point of view is worth a bit of thought.

Olly

[Earl]

dont some single arm mounts do away with the need for couterweights as such?

[ollypenrice]

52 minutes ago, Earl said:

dont some single arm mounts do away with the need for couterweights as such?

Yes, and this is another avenue. Really, a single arm variant of the fork might be the answer for light mobile setups. Good point, Earl.

Olly

[Whirlwind]

5 hours ago, Tommohawk said:

The dec drive and clutch is mounted at the top of the mount unit, just under the puck. But why dont they fit the drive and clutch underneath on the counterweight side? This would bring the scope closer to the axis by approx 75 mm and reduce the CW mass by errr...... gropes for calculator.... quite a bit. 25%?

I cant see why this wouldnt work - yet all the brands seem the same.

Any thoughts?

 

The Vixen SX.. and AX.. range do this.  The motors act as part of the counterweight as in your example.  I have the old Sphinx SXD and it makes it very portable (I can lift it with one hand). 

[Tommohawk]

6 hours ago, andrew s said:

I think it is best mechanically to have the main load (the scope) as close to the top bearing and point of drive as possible. This increases the torsional stiffness of the drive. Indeed on the Paramount the top bearing and worm drive are integrated together.

Regards Andrew

I agree its best to have the scope as close to the to bearing as possible - and mounting the drive underneath would help achieve this. I take your point that this increases the separation between the driven part of the shaft and the scope, but I think there would be minimal torsional flex as there is no resistance to rotation other than inertia.

5 hours ago, ollypenrice said:

One portable rig one idea that came up at our dinner table was to use the battery as the counterweight. I think one firm has started doing this now? I also think you're right that optimizing the position of the saddle plate from a C of G point of view is worth a bit of thought.

Olly

Using the battery as a counterweight - now I like that idea. I did consider using a fluid filled container such as a dumbell weight - there are water filled versions of these available. In fact a fluid filled weight could double as a handy beer decanter. Hmmmm.... you'd have to wait til you were done before drinkng the beer though. 

2 hours ago, Whirlwind said:

The Vixen SX.. and AX.. range do this.  The motors act as part of the counterweight as in your example.  I have the old Sphinx SXD and it makes it very portable (I can lift it with one hand). 

Now that's the thing!! (tears up patent application form) Yes, that would do nicely. I'm surprised this design hasnt been more widely adopted. It only saves a couple of kilos in counterbalance, but marginal gains and all that. 

Its a shame I dont have a workshop otherwise I think I'd try and cannibalise/modify/probably destroy a Synta mount.

Thanks to all for the ideas!!

[andrew s]

33 minutes ago, Tommohawk said:

I agree its best to have the scope as close to the to bearing as possible - and mounting the drive underneath would help achieve this. I take your point that this increases the separation between the driven part of the shaft and the scope, but I think there would be minimal torsional flex as there is no resistance to rotation other than inertia.

It may be small (even minimal) but designers have generally moved away from doing this for good reason. With the trend to lighter mounts with minimally sized shafts the effect can be significant and impacts the control characteristics of the drive especially with a heavy telescope.

Regards Andrew

[Tommohawk]

Quick follow on in case any follow this (probably me at some point in the future when I've forgotten) the Ioptron EQpro has a similar design ie dec drive on the counterweight side.

Ioptron EQpro mount weight 2.8kg, 1.25" steel tripod 2.6kg, load 5kg (ex counterweights) price ~£450

Vixen Sphinx SX2 mount weight 7kg (tripod excluded?) load 12.25kg. UK price?? $1800 or 1800euros)

Vixen SXD mount weight 14.4kg (no tripod) load 15kg for imaging, price $2300

[Waldemar]

Ioptron had some very nice ideas ... like batteries for cw... for quite some time already