Hey All,
I'm working on a project to revive an old motion control rig for stop motion animation. I've had success testing with a single stepper motor, Arduino Uno and Easy Driver. To hook up the whole rig I'll be upgrading to Arduino Mega and Big Easy drivers for each of the 6 motors for the various axis: (x, y, z, zoom, tilt etc).
My biggest unknown and concern is how to power these relatively large motors. They're rated at 2.3V, 2.7A.
From what I understand I should be going for ample power that the Big Easy drivers will regulate. My guess is 12V , maybe 18A power supply?
Switching seems like a good idea?
Can all the drivers be wired into a single power supply or is there some intermediate board I should use?
There wouldn't be a constant load, but there would be long pauses (during shooting) when the motors are held. I'm thinking a cooling fan might be a good idea but I don't expect this would affect power consumption much
You will get better performance from the motors with higher voltage - perhaps 24v or 36v
Strictly speaking each motor needs about 2.3 * 2.7 * 2 = 12.4 watts (roughly). Six motors would need about 75 watts. At 12v that would require (say) 7 amps. At 24 volts only about 4 amps would be needed. Personally I would add a margin of error and a big capacitor for the power supply to each stepper driver. I don't thing 18 amps at 12v is necessary.
Hopefully you will get a second opinion on this. (And do check my maths)
MarkT:
Can you use smaller motors with gear-reduction?
Unfortunately the motors / belt drives and frame aren't negotiable since I've already got them set up. It was once a very expensive piece of equipment and my job has been to get it running with modern software. Its basically an aluminum robot with belt driven gears and threaded shafts that move a DSLR camera through a space while shooting photographs. Its range of motion means it occupies a lot of space, like the size of a walk in closet or something like that.
So far I've had success on a small scale testing the motors with the new software so I've got the go ahead to apply that to the whole rig.
I'm going to go for @Robin2 's recommendation as it would be rare that all the motors will be operating at the same time, and even then for short bursts. Thanks guys.
Steppers draw maximum current from their terminals at stationary, however when
operated from chopper drivers the current into the driver increases with load and speed
to provide the larger voltage (and thus power) requirements.
Its a complex function of the various parameters, but lets say you have
N motors each rated at I amps and resistance R:
each motor at stationary consumes power I^2.R
each driver uses power k.I^2.R (k might be about 1.2, due to inefficiencies in the driver).
Thus if the supply voltage is V, you'd take about N.k.I^2.R/V amps to power the drivers.
Here N=6, I=2.7, R=0.85.
Choosing V=12 suggests 3.7amps (assuming 75% efficiency from the drivers). However
this would increase quite quickly with speed as 12V is quite low.
Choosing V=24 suggests 1.85A for stationary, increasing less rapidly with speed.
My vote would probably be 24V 5A, but in reality I'd try the system (well a single motor
+driver perhaps) on a bench power supply to see how it fares under various voltages.
See this is why I come here!
I'm doing some electronics tutorials to improve my basic understanding of all this. But really you guys are making me look like a genius to people here at work.