Hi, I am just looking at polargraphs and drawing machines. My first thing is looking at the motors. I see that some designs have 200 steps pre rev and others 400 steps per rev. Also, current, voltage?
1) What is experience of 200 vs 400 steps per rev?
2) Any experience with different voltages/current?
2b) Do you find motors getting hot/ pushed to their limits with their long drawing times?
3) I saw on one of the last posts that Torque wasn't a huge factor.. can you describe that again?

Thanks!!
Rachel

I think I'd agree with all of that, definitely.

In principle, 400 step motors can be twice as precise as 200 step motors. In practice, either way the smallest unit of movement is still a fraction of the size of the blob of ink at the end of the pen. I expected to, but have never found a case where I needed the finer motors, so the new PolargraphSD uses 200 step motors.

How hot your motors get depends on your motor drivers, supply voltage/current and your motor rating. The first motors I used, those little 400 step NEMA-16 motors were just fine with the Adafruit motorshield because it could drive them nicely at 5 or 6 volts. Using them with the Polarshield (PolargraphSD), or generically with the A4988 stepper drivers (like stepsticks) they turned out a little under-sized. Those stepper drivers are a bit clever-clever, and require a supply voltage of at least 7.5v, and that was at the upper limit of what I was happy putting in those motors. They get quite hot. If the drivers are tuned then they're still very usable, but they do get uncomfortably hot.

The motor drivers on the adafruit motorshields cannot be adjusted, so it's more important to get the right sized motors to fit it.

Long drawing time didn't make much difference for me - it is being locked in one place that really sends the temperature up, rather than continuous use. Continuously, a stepper motor is always chopping the current into little slices - it's never really "full on", but when you stop moving then there are two coils that are full energised, and they heat up. There is a time-out in the firmware that cuts the power after 5 minutes of inactivity.

If you are sourcing your own motors, current rating is the main specification to look at, and it should be less than what your motor drivers are capable of providing. So if you are using a Polarshield, which has A4988 stepper drivers onboard, then you can use a motor that will draw up to around 1A.

If you are using an Adafruit Motorshield v1, then it has L293D H bridge chips as drivers, and they can provide 600mA of current, and so your motors have to draw 600mA or less. Etc.

Voltage isn't that relevant to stepper designs, but I would steer clear of motors listed with very low (less than 6v) or very high (more than 12v) voltage rating.

wanderson is exactly right about the torque requirements too. The only times that torque is really a problem is when the gondola is right up at the top of the machine, and so the two motors are pulling against each other. Can usually be solved by adding a bit of weight to the counterweights to bias it in that direction.

good luck!
sn

Ho Dazzled, current rating is about how much the motor will draw. If the motor draws more than the driver can supply, then the driver will overheat.

The very first pair of motors I got were big 2 amp things. I got them because they had low voltages, so I thought they'd be easy to drive. I fried a couple of motor shields with that setup. They worked, to an extent, but movement was weak, and unreliable. Actually I think the thing that gave out first was the power supply which was one of those cheapo 350ma ones.

Even with piggybacked driver chips, you're still pushing the capabilities of the L293D driver chips, so personally, I wouldn't try using them.

Sn

From https://learn.adafruit.com/adafruit-motor-shield-v2-for-arduino/overview

we now have the TB6612 MOSFET driver: with 1.2A per channel and 3A peak current capability

So, it'll probably run better, but I still think it's not a perfect match. Also I'm not a big fan of the new motorshield, so I don't think I would recommend that. Get some motors that fit the drivers is best.

sn

That's excellent news, great to hear. I found it really hard to figure out how to buy the right sized motors - slightly trial and error. I just didn't know enough. So this makes that a little less important.

I had read adafruit stuff that suggested there were diminishing returns when it came to stacking more L293Ds. It's also possible to use SN754410 chips, which can handle more power to begin with.

Thanks for the feedback.

sn