Stepper motor: amount of steps and voltage requirements

2.2mm will only be effective for wide- to normal-angle lenses. Using anything longer will result in very fast movement (i.e. limit your speed options). Also, I presume you're calculating 2.2mm based off of final gear travel? Don't forget, the calculations for travel for _that specific motor_ includes the gear-down divider. Without a gearbox, you're talking 1/200th your final drive ratio.

An additional thought - your _minimum_ movement would be 2.2mm. Consider ramping -- do you want to ramp into your max speed movement? If your max speed movement is 6.6mm, that leaves you only three steps between minimum and maximum speed. So, if you're trying to do a smooth ramp (as in ramping into the motion in the final output video), you'll need to choose a max speed many times your step rate to do a smooth transition into the full-speed. That may be way too fast for your output video. I generally prefer more resolution (smaller step amount) to leave flexibility for ramping at any reasonable speed -- including very slow.

The 17YPG is a preference due to the ease of use (only final drive gear needed), high torque, and low power consumption due to the gearing.

48 steps per rev though? This is pretty uncommon for high-torque motors. 200 steps/rev (1.8') is the most common and some places make 400 step/rev (0.9'). I don't see what you save, unless you're talking those cheap round steppers that they sell for a few bucks at a lot of resale outlets. Those aren't worth a penny in a system like this. They are less reliable, have less torque per milliamp consumed (generally speaking), and have lower life-spans than the square high-torque steppers which are highly common. (Now, if you're talking some monstrous industrial stepper, you probably don't need that either.)

Where are you looking at motors? When you say "most motors seem to require more than 12V" that doesn't jive with my experience, which has been that most motors are badge-rated at only a few volts, and some are rated higher. Of course, some specific vendors may cater to a particular usage, which results in them rating towards systems they intend for them to be used in. Any stepper can be run at a higher voltage than its badge rate. Running motors at a higher voltage is done to increase velocity (rate at which the motor comes up to speed) and achieve a higher max speed (IPM or MPM in CNC nomenclature) while retaining torque. Generally speaking, unless you're moving dozens of lbs and trying to frame-sync with a Phantom, you won't need those speeds or velocities. There are plenty of motors whose badge are rated at 12V or higher, but they are generally going to be overkill for most applications. Don't look for a badge rating >= 12V, look for low current consumption and a low voltage (more headroom to drive it at a higher voltage) - with a higher torque value. Often, one can get much better performance out of a motor that doesn't seem as "powerful" as another.

The motor and the arduino should, effectively, always have separate supplies. Only GND is shared between the driver and the arduino. You can lead them both off of the same battery when running 12V (or lower).

!c

Hi Leo, sorry for the edits as I'm going along - I realized I was running late for a meeting and hit send before proof-reading *grin*.

The NEMA sizes just refer to the mounting hole orientation, and the distance between each hole. It's just so you can swap two motors of the same NEMA size. Generally speaking, larger NEMA sizes can result in greater torque, as there's more room to wrap wire in the shell, but that's not always true. =)

At 30 oz/in of torque, that would result in less than 2lbs of torque if it were driving a 2" diameter pulley. Not likely to be effective for your needs. Without a gear chain, or a _very large_ pulley, you'll want to hit a torque rating at least 1.5x-2x your actual load weight. So, if you're pushing a 10lb cart, and you have a 2" pulley (which results in a 1" lever executing the torque), you'd want at least 240-320 oz/in torque motor.

Edit: I read the wrong motor, it's 62 oz/in, which results in about 4lbs of torque w/ a 2" pulley. Still likely to be too low.

You can do gear reduction, which will increase the torque and resolution, however. That's why we like the one we reference in the dolly design, it has a fairly high gear reduction, so uses very little energy to achieve lots of torque.

!c

The one issue with those gear motors from Anaheim, is that they aren't always in-stock. That's the major bummer, as it can cause a wait of several weeks. Conversely though - that's about the least expensive you're going to find a stepper motor + gearbox combination with that reduction ratio.

Shipping will probably be pricey, but not that bad as its a small box. =)

For the ones we got for that prototype, we paid an extra $70 to rush the order (two weeks vs. eight for out-of-stock) and then the price listed, I think it was around $65-80 IIRC for the motor+gear combo. Shipping was pretty cheap to CONUS, < $10.

These guys are in the UK, and they have a 42:1 planetary head for a NEMA 23 frame size for 100 lbs: http://www.motioncontrolproducts.co.uk/product_info.php?cPath=1036&products_id=60&osCsid=7528d1f44bf1175a2a543b42802a16cd - but the backlash is pretty tough on that one.

Additionally, here's a worm gearbox, sourced in the UK: http://www.ondrives.com/gearboxes-reducers-wormwheel-gearbox-pf20nm-nema-17.html

But, at those prices, shipping might not seem so bad =)

It's worth noting, if you got the 100:1 gearbox listed above, that would make the 62 oz/in motor a 6200 oz/in output! And give you resolution of 2,000 steps/revolution. It would force slower movements, but excellent power. Just have to make sure the shaft will fit.

!c