[macskyver]

I am in the process of developing a linear bipolar stepper motor driver. It is similar in concept to the Linistepper with the main difference being that it is designed for bipolar stepper motors rather than unipolar stepper motors. The benefits of this kind of driver are:

-runs smoothly
-runs quietly
-less heat generated in motor

The drawbacks are:

-relatively complex circuit
-lots of heat dissipated in driver circuit (which also limits drive voltage)

The main reason I started this project is because when driving my 3D printer steppers at moderate speeds, the steppers would get hot and eventually start skipping due to the decreased torque. This happened even when driving the stepper quite a bit below their rated current. So after doing a bunch of research, it seemed that a linear stepper would fit my needs best. Unfortunately there doesn't seem to be many drivers like this on the market, so I decided to build my own.

So far I have built a functional prototype and it works great. The current waveform through the motor is a very nice sine wave. At this stage I am updating the circuit (mostly to reduce physical size) and I figured this would be a good time to get some input on whether or not there is enough interest in this to be commercially viable, and if so, what features people would like to see.

Right now the peak output current is adjustable from 1-5 amps with a potentiometer. It is set up with 16th microstepping and there are currently no external microstepping mode adjustments. The control inputs are step, direction and enable and can handle logic from 1 to 20V. Power input is 5-24VDC.

If anyone has any questions, comments or ideas, please let men know. Thanks.

[doorknob]

It sounds like an interesting project. Does it look like the heat sink requirements for a higher amperage driver will still be feasible? IIRC the Linistepper heat sink gets pretty toasty even at moderate currents.

How will the current setting work? Do you adjust the pot to achieve a specific voltage reading at a test point? I've never been very keen on drivers that use a trimpot adjustment to set the current, since it always seems difficult to get it exactly where you want it to be. Will you be able to adjust it independently of whether or not a load is connected to the driver?

The supported voltage range seems a bit on the low side if higher-speed performance is an objective (but I understand that increasing the supported max voltage may have undesirable ramifications, both in the expense of components and in the power dissipation department). If you're looking at supporting higher current ranges, your target motors are probably not just limited to small NEMA 17's, and also probably not limited to running small 3D printers, and so achieving adequate torque at higher speeds will be an issue for some users and applications.

[macskyver]

The heat sink requirements shouldn't be too bad for moderate amperage. On my prototype I was running 2-3 amps (peak) with medium sized TO220 heat sinks and no fan. At 2 amps it was warm, but not uncomfotable (best guess around 50C). At 3 amps it got a little uncomfortable, but not excessive.. This was running a nema 23 stepper motor (rated at 3.6 volts I think) with a 12V power supply. Running higher current with a 24V power supply will obviously be more taxing, but a fan goes a long ways.

The pot current setting will be read in the setup code when the microcontroller starts up. Then it generates the sine lookup tables with the amplitude based on the previously read pot setting. The DAC outputs the sine values to the current control part of the circuit where the voltage (after going through a divider) is compared with the sense resistor on the H-bridge. One good thing is the poteniometer is full range and interpreted by software.. so if you want it to adjust a very specific window (ie 2.2 - 2.3 amps), you can do that. Also, I can use a multiturn pot, which is what I typically do for stepper driver circuits. The poteniometer can be adjusted at any time with or without load.. To implement the changes, all you gotta do is hit the reset button

Yeah I am sorta limited on supply voltage, but this driver is primarly meant for 3D printers where most people use 12 and 24V. I should also clarify on the desired speed. I was referring to linear travel speed, not necessarily motor speed. Right now I am driving a 36 tooth GT2 pulley (72mm circumference) directly so it doesn't take very high motor speeds to get the printer zipping along. You are right, my target motors aren't limited to NEMA 17s. I was thinking it would be for NEMA 17s and 23s.

[levon18lopez]

linistepper working with bipolar stepper motor..... can yo share some files.. eagles cad and hex and more

[macskyver]

I kinda tabled this project a while ago. It worked well at low speeds, but the waveform got pretty distorted at higher speeds. I didn't really have the time to pursue it further. If you want, PM me an email address and I'll send you all the files I have, although I will warn you there is probably a decent amount of work left to get it usable and I think changes need to be made to the circuit boards.

[James Newton]

I'd like to make those files public. Since they are based on the Linistepper, in the spirit of open source, I really think that would be... right.

[macskyver]

You are more than welcome to make the files public. I would just want to send you all of the files via email with a detailed description of the state of the project and where known errors are in the files. I am all about being open source, but just so you know, this project is not at all based on the Linistepper.

[James Newton]

Ah. Sorry if I misunderstood. I very much appreciate your dedication to open source. My email is JamesNewton @ MassMind.org

[macskyver]

Ok, files are sent. The email got kicked back a couple of times presumably because I had attached zip/tar.gz files.. I renamed them to .piz so hopefully that will make it through.