Electronics help needed - rather urgent!

Hello all,

I'm currently designing a 3d printer that will use 2 linear actuators (these badboys)to extrude paste from 2 syringes.

My question is this: Will they operate with a normal 3d printer setup (ie 4 NEMA 17s for the axes, a heated bed, and possibly a fan all running through a Arduino Mega fitted with a ramps 1.4 board)??? Are there any power issues i should be watching out for (maybe not enough current to go round between all hardware during a print)??

Thanks

Yep shouldn't be a problem at all, they would just be in place of extruder motors

Thanks lazzymonk, that gives me more confidence!

I had a look at the specification pdf just now - the motor is rated at 12V 0.4A. Would it actually receive a full 12V from a pololu A4988 driver?

12V 0.4A seems to be the wrong kind of motor 12/0.4= points to a 30 ohms coil. Imo find something like ~1~2~3 ohms coil. The usual and good motors are rated like 2~3~4V and 1~1.5~2A something more along those lines instead.

Thanks for the clarification, NoobMan - much appreciated.

We're currently looking for linear actuators in the UK and seem to be consistently hitting a cost limit of around £55 (which is probably a decent price), and lead times of 4 weeks minimum. Thus, we've been looking around some USA site too (such as koco motion) who seem to have much more stuff available. Has anyone had experience with US companies exporting to the UK?

Also to add to the questions regarding motors, If I am using a pololu driver (A4988 for example, 3.3V or 5V, 1A etc) what would be the difference in performance between a linear stepper motor rated at 2.33V 1.5A and one rated at 5V 0.7A?

Quote
DMTDisaster
Also to add to the questions regarding motors, If I am using a pololu driver (A4988 for example, 3.3V or 5V, 1A etc) what would be the difference in performance between a linear stepper motor rated at 2.33V 1.5A and one rated at 5V 0.7A?

Imho go for 2.33v 1.5a, much better. Just to be clear, the 1.5A rating is a maximum of what the motor can handle. The driver will have an adjustable pot which will be used to set the current (peak) at probably around somewhere 0.7-1.2a.

Thanks again NoobMan!

I was originally also worried about oversupplying the motor with too much voltage, but seemingly found that with these kinds of motor drivers it doesn't seem to matter how much voltage you put through it as long as it's within the operating range of the driver. Or at least that's what I gathered from reading around the topic.

How can I work out the output torque if there isn't a specific voltage being supplied? Do I simply assume that power is calculated rated voltage multiplied by the max current that I have allowed to be supplied to the motor? Then torque is power/angular velocity.

Just regarding the motor alone, you could theoretically put voltage up to the coil insulation max, which is usually something like 400vdc or so. But the driver input is probably more like 30-40v max to start with.

The torque simply does not care which voltage is it, only current. But there is a dependency between them in the sense that the voltage across the coil builds the current rise, and the problem arises when the voltage is so low that current does not rise fast enough - thats when voltage matters, but that is because voltage is too small. If the voltage is "too high", it does not matter because the current reaches the set peak after which voltage is interrupted. So a bigger voltage does not do anything, except it gets the current to "erect" faster thats all.

Dont go with the "apparent power" formula for the power or the stepper. As a large abstraction or just to compare ratings between motors maybe. But for actual standalone calculations, cant. Because the voltage is switched all the time, and you dont know how much is on/off so it would require some kind of average figure. The current we set is the peak value, where it gets interrupted, but peak is not an average either. Its worse, it has rising edges and just if we know whats the interruption point doesnt mean we know all the values to get there. It could get to that peak very fast or very slow, and results will differ by much. And even worse, the falling edges are nightmare in math terms as they can have synchronous rectification or output diodes and even some remainder of blank time, so the general shape of fall edge is not all that clear. So all this is just a bit too much to just make p = v*i and expect a result to mean something by itself.

Thanks Noobman,

I have now been looking at a canstack linear actuator - this guy (the non-captive, bipolar, 7.5deg/step, 5V)

It has been rated 5V and 561mA per phase. I don't want to run the motor at full capacity as it will break/run into problems sooner rather than later.

For the purposes of it's performance, if I half the current supplied to it (i.e. set pololu driver current limit to roughly 280mA), should I expect half the torque/force? (From looking at the performance graphs i see that torque is influenced by the speed that it is run at, but the minimum force at the linear travel i'm interested in (0.013mm/step) is still larger than what we need, and that the motor would be run at a constant speed)

Edited 1 time(s). Last edit at 02/11/2014 07:45AM by DMTDisaster.

Dont think those would work fine with usual pololu drivers. First off, two of them have 52ohms resistance and 0.23A current, those are pretty much the wrong type. The others two are 8.9ohms and 0.561A, that is slight improvement but not by much.

Ideally would need something like 4ohms or less, and current to 1A or more. I would take a regular reprap motor, add a screw to their shaft, and just use it like that.

Thanks Noobman, think we'll be going with these instead. There is a 2.33V 1.5A linear actuator which should be perfect (i hope). We were checking out can-stack actuators since they are slightly cheaper but, like you said, don't seem to fully meet performance criteria.

I was also looking at buying a Xbox 360 power supply rated at 12V 203W. By my calculations that should give roughly16.9 A. I've read that a heated bed requires 11A, would that leave enough current for the other motors? ie. should i count the motors' current requirements as that which will be coming out of their drivers (ie what I limit them to).

Yes the one with 1.5A and 1.56ohms sounds much better. What that page calls "operating voltage" is only the product of these two numbers, not the "real" operating voltage which the motor is to be supplied with.

About the consumption, dunno really, but could take like 1A in budget for each motor. For an 20x20cm bed you would need at least 100+watts, you need to know how much resistance it has in order to see how much current it draws. I dont know if that 203w is the input power or the output power. But i will guess its an input power, and like an smps will have an efficiency lets say 75%, then the output is more like 12.6A instead, which likely wont be enough.

Thanks again, Noobman. Things went quiet for a bit, due to report writing etc.

Looking up some ATX power supplies now, will probably fit the bill, although pretty large...