Why use NEMA17? Why not a NEMA11 or NEMA14?

[brownrb]

The reasons are simple. Yes, its heavy and big.

So why did I recommend it?

1. A stepper motor may be the most expensive single purchase, no point buying one then havong to replace it later

2. To get enough torque it really needs to run off 12V

3. The BY 5V geared motors are cheap, have a good deal of backlash, but if you are using a filter wheel and decent ccd, they DO NOT have enough torque to either move or hold the imaging train in place. May people go with those BUT they do not bother to test when the telescope is pointed to zenith, where the highest load is taking place.

4. Why not the NEMA 14 or NEMA11. Good question, BUT, torque is a function of voltage and current and resistance and magnetic force, size of magnets, number of coil turns etc. You will find that the NEMA11 and 14 need HIGHER currents to get the same level of force as the Nema 17. Why? Because smaller maganets, less coil wires means less force, so to compensate for that you must increase the current. So the nema14 current is > 0.6 amps vs the Nema17 at 0.4A

Does 200mA make a difference, yes, has implications on driver board choice but all HEAT is a factor of coil resistance, voltage and current, so that means the Nema11/14 will run much hotter than a NEMA17. Because the coil resistance is so low. This then has flow on effects to voltage supply, current loadin on the driver chip etc.

The smaller motors will need to have coil power ON when not moving in order to hold a heacy imaging train in place (because torque etc is a function of size of motor, voltage, current etc etc). A larger motor always generates more torque. IS it overkill, probably not, it will work even for the most serious user.

And yes, you can rotate the focuser so the stepper is upright over horizontal. Overcomes balance issues if you have them. So why would one begin to compromise, the 11/14 are much the same cost as a 17 and if one ever got a heavier imagmeing rig then one would not have to shell out more money for another stepper.

Anyhow, thats a brief summary of my position. Whilst a cheap one may work for some, I wanted to recommend one that works all the way from beginner to very serious.

Cheers

Robert

[JoBarTeam]

Hello,

Agree with Rob, i buy a nema 14 (1,6kg torque) and a nema 17 (30kgs torque).
With the Nema 14 and coil power on, i can rotate the shaft by finger, impossible with the nema 17.

They are less than 1cm between nema 17 and nema 14...

Nema 17 is better

[brownrb]

I posted that because there has been feedback on another forum. Its hard to cater for all different tyoes, if you are ever only have the budget for 1 stepper motor, you may as well but the best you can get that would suit all sorts of things you can throw at it?

[JoBarTeam]

I make a mistake when buying the nema 14.

They look the same but the nema 17 is thirty times more powerful
Nema 14 is limited with FW + barlow + ASI120MM.

Finaly, i buy the nema 14, 19€ (same in $) and my nema 17 20€....