[ChrisH]

ArmoredFairy698

The basic question is how much WORK you want to do while extending the telescope. Work=Force*distance. So figure out what you want to pick up, how much it weighs and how high you want it to go. The next thing to think about is how fast you want the Work done. This tells you how much Power will be required, because Power=Work/time. Power is also equal to Torque*Rotational Speed. By using these simple relations you should get a good idea of what size and speed of motor will do the job you have in mind, and how much gear reduction will be required to get it to work.

A couple of other things to consider. Electric motors are happiest if they are running at 75% of free speed or 25% of stall torque (typically they are the same place on the torque/speed curve) . So you want to plan around those numbers. You also need to subtract a certain percentage of available torque to allow for losses in the sliding system. Once you have a rough idea of how much power you need and what the moments will be, it would also be a good idea to estimate the weight of your arm and include that in your work calculations.

Yes, I know you just calculated stuff, but remember "Design is an iterative process" get used to doing this sort of thing over and over again. I highly recommend learning to use a spreadsheet for this sort of thing. It makes it a lot easier.

If you give us a better idea of what you are trying to do, we can walk through the calculations here. Doing so will be a good learning experience for all.