10” Equatorial Platform for Dummies

[PeterStudz]

@G_N - you might have seen the Sky at Night EQ Platform build…

https://www.skyatnightmagazine.com/advice/build-a-dobsonian-equatorial-platform

It’s not quite the same design but similar. And it does go into some of the calculations. Like here… all a bit too complicated for me! But it might help.

https://c02.purpledshub.com/uploads/sites/48/2018/12/SAN15001geometry-cb34dca.pdf

 

[PeterStudz]

There’s also an EQ Platform Group. Not sure how active it is but you could try posting there too…

https://groups.io/g/eqplatforms

[G_N]

10 hours ago, PeterStudz said:

@G_N - you might have seen the Sky at Night EQ Platform build…

https://www.skyatnightmagazine.com/advice/build-a-dobsonian-equatorial-platform

It’s not quite the same design but similar. And it does go into some of the calculations. Like here… all a bit too complicated for me! But it might help.

https://c02.purpledshub.com/uploads/sites/48/2018/12/SAN15001geometry-cb34dca.pdf

 

Thanks I saw that, but as you say it's a different design.

[G_N]

12 hours ago, Ratlet said:

Great minds think alike @G_N!  You're making your base the exact same way as me.  I'll try to get a look at my plans tonight as I can't remember exactly how I designed mine.

With regards to the templated segments they will work well enough because for the Dobs that they are designed to fit they are all more or less using the same design.  For a generic design you can also largely ignore the centre of mass of the solid tube the itself as it will more or less be in the middle of the base.  You are correct though that if the design ends up out of balance you'll find the motor won't turn it.  If you have a look at some threads on the forums youll see cases where people have had to use additional/different motors or teeth, rubber strips etc to get additional torque.

 

Thanks. I'm not sure what you mean when you say I can "largely ignore the centre of mass of the solid tube the itself as it will more or less be in the middle of the base"? Which solid tube do you mean?

[Ratlet]

33 minutes ago, G_N said:

Thanks. I'm not sure what you mean when you say I can "largely ignore the centre of mass of the solid tube the itself as it will more or less be in the middle of the base"? Which solid tube do you mean?

Sorry, I was meaning that for an EQ platform part of the calculations involved figuring out where the centre of gravity of the dob is centre of gravity of the solid tube telescope and the base.  I'm referring to the solid tube of the actual scope.

In most cases the scope itself will be balanced or very nearly balanced so that the centre of gravity will be bang in the middle where the pivots are.  It'll behave as if it were just a weight at the height of the altitude bearing.

Essentially there are only so many ways that 8"-12" dobs are built (solid tube telescope particle board/plywood base) so that a generalised design will work in most cases without being unbalanced.

[Duotwr]

Hi everyone,

competent DIY-er here, but beginner astronomer! But I love a building project (trying to get my teenage daughter to help) - but I need some advice...

I'm based in Glasgow (56 degrees latitude approx) but not inconceivable I might have a chance to use the telescope further north, potentially up to 58.5 degrees north). I see the VNS designs don't provide segments for this high - is that because I'll hit some kind of limit? Is there a preferred design approach for platforms for this far north?

thanks

Keith

[PeterStudz]

2 hours ago, Duotwr said:

Hi everyone,

competent DIY-er here, but beginner astronomer! But I love a building project (trying to get my teenage daughter to help) - but I need some advice...

I'm based in Glasgow (56 degrees latitude approx) but not inconceivable I might have a chance to use the telescope further north, potentially up to 58.5 degrees north). I see the VNS designs don't provide segments for this high - is that because I'll hit some kind of limit? Is there a preferred design approach for platforms for this far north?

thanks

Keith

For visual and that’s what designs like this are about, you’ll be fine. The commercial platforms often have a 5 degree suggested range. Like this…

https://www.firstlightoptics.com/equatorial-astronomy-mounts/omegon-dobsonian-polar-wedge-tracking-platform.html

[Ratlet]

I'm in the process (still) of designing one for 57.5°.  I suspect why they all in one design taps out at 56° is because the southern bearing starts to come in close and potentially go under the dob base as it approaches 58°.

Like Peter says though these are designed for visual and helping stop the target yeeting out of the fov so close enough will be good enough in much the same way that I can plonk my eq mount down at about the right position and still get the target to remain in the fov.

[PeterStudz]

25 minutes ago, Ratlet said:

I'm in the process (still) of designing one for 57.5°.  I suspect why they all in one design taps out at 56° is because the southern bearing starts to come in close and potentially go under the dob base as it approaches 58°.

Like Peter says though these are designed for visual and helping stop the target yeeting out of the fov so close enough will be good enough in much the same way that I can plonk my eq mount down at about the right position and still get the target to remain in the fov.

Both of these points are very valid. And of course an EQ platform is generally just plonked down, facing north via compass. Here, there will potentially be the biggest “inaccuracy” as it isn’t accurately polar aligned. But for visual it doesn’t matter. 

[G_N]

On 08/10/2024 at 23:10, Ratlet said:

Sorry, I was meaning that for an EQ platform part of the calculations involved figuring out where the centre of gravity of the dob is centre of gravity of the solid tube telescope and the base.  I'm referring to the solid tube of the actual scope.

In most cases the scope itself will be balanced or very nearly balanced so that the centre of gravity will be bang in the middle where the pivots are.  It'll behave as if it were just a weight at the height of the altitude bearing.

Essentially there are only so many ways that 8"-12" dobs are built (solid tube telescope particle board/plywood base) so that a generalised design will work in most cases without being unbalanced.

Yes, the centre of mass of the OTA will be - for all practical purposes - in the centre of the tube, at its balance point in the cradle.

That's fine, but the base itself has significant mass, and you need to design the platform to the centre of mass of the assembly. In our case it's about 210 mm below the OTA's centre of mass - so it's probably a significant consideration when you're trying to rotate that much out of balanced mass with an 8mm diameter drive.

[westmarch]

16 hours ago, G_N said:

Yes, the centre of mass of the OTA will be - for all practical purposes - in the centre of the tube, at its balance point in the cradle.

That's fine, but the base itself has significant mass, and you need to design the platform to the centre of mass of the assembly. In our case it's about 210 mm below the OTA's centre of mass - so it's probably a significant consideration when you're trying to rotate that much out of balanced mass with an 8mm diameter drive.

Hi there,

I think the point that the others are trying to make is that our experience is with commonly, commercially available 8-10” Dobs and the combined assembly is stable on the platform.  We haven’t done the COG calculations and so it comes down to whether you want to see if it works for you. 🙂

John

[G_N]

On 14/10/2024 at 10:41, westmarch said:

Hi there,

I think the point that the others are trying to make is that our experience is with commonly, commercially available 8-10” Dobs and the combined assembly is stable on the platform.  We haven’t done the COG calculations and so it comes down to whether you want to see if it works for you. 🙂

John

OK understood, thanks.