G_N

OK understood, thanks.

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.

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?

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

Evening all - this is my first post, but further to Nathan's question earlier on this page (we are trying to design a platform for my 10" Starfinder and home made Dobsonian mount): We have followed Vogel's explantions, and have got some way into designing the platform, however, there are a few things that aren't clear: 1) Once you've got the Circular Segment positioned correctly (perpendicular to the north axis), it's easy enough to project the section when looking "straight-on" to the platform (ie it forms an ellipse) , but for the rotation to angle the segments relative to the centreline, where are the axes you rotate the each segment about? It's a vertical line somewhere offset each side of the platform centreline, but where isn't specified. Presumably if it's wrong, the rotation of the platform won't be correct? 2) I don't understand how the templated segments work: I understood that the whole Equatorial platform design was based "heavily" (ha ha) around rotating the telescope and base around it's combined centre of mass. But I can't see where this is accounted for in the plans that use the templates? Surely if this is wrong, then the platform could fail to work due to the motor not being powerful enough to turn a potentially grossly out of balance assembly? This is why we'd like to know the diameter of Vogel's initial Circular Segment - so we can ensure it's positioned such that our centre of mass is on the rotation axis, and then we can confirm that our geometry is right because or CAD for the segments should still match Vogel's templates. We are at 53 degrees North btw. We are using Fusion 360 for the design. Any comments much appreciated! Thanks.