General motor speed and torque question

  • This might sound odd, I am trying to choose motors for a custom machine I am building and need to pick the right gear ratios for the right torque and speed values for a machine.

    How much torque is too much? haha What is the upper limit for speed that the motors are going to hit in a GT2 16 tooth configuration? I would only expect a few hundred rpm.

    Is 400 mNm of rated continuous torque the range I should be looking for? I want to make sure I pick the right motor size and gear ratio. This is not for the Z-axis on a cartesian system, I am thinking a Kossel right now. I am thinking of Gates GT2 belt only because the torque required to drive a screw like the zero backlash igus lead screws I have require similar force to turn as the output shaft on my 40 mm 5.18:1 Nema 17. Driving a screw will require much more force than a belt system right now. I think doing this for a Kossel is easier right now.

    This is rated (if my calculations are correct) at about 210 rpm @ 24v. Forget the majority of other motor data right now. I am mainly interested in the torque for continuous and holding torque as well as the speed requirements of the output shaft of the motor for a Kossel. What is the fastest and highest torque requirement?

    For the screw I have, I am thinking of triple or quadruple that continuous torque value and around 30-50 rpm, if anyone is interested.

    More speed? More torque? I'd like some thoughts.

    The motor I am thinking of replacing my current Nema 17's has a continuous torque of 400 mNm @ ~210 rpm @ 24v. It is about half an amp according to the datasheet, but that is just the rated values for continuous operation. Little geared motors so I can always jump up in size if more torque at higher rpm is needed.

    I am working on something you might like muahahaha

    Thanks in advance.

  • administrators

    For the speed at which torque starts to drop off, use the calculator at

    For a Kossel i suggest you aim for at least 200mm/sec XY motion.

    Half an amp rated current is much too low. The motor will have high inductance and this will reduce the speed at which torque drops off.

  • @dc42:

    For a Kossel i suggest you aim for at least 200mm/sec XY motion.

    Half an amp rated current is much too low. The motor will have high inductance and this will reduce the speed at which torque drops off.

    I am not using steppers. The amperage is low because of the motors I am using, the dynamic friction of the motor is near zero without a gearhead. Moving a piece a paper requires more force, it is actually genuinely difficult to believe. The motor company knows what I want to do and this is the motor I am thinking of using.

    Or I was thinking something like this but with a 5mm shaft with a flat edge or a laser welded GT2 16 tooth pulley on the end (they will do that for me).

    I am already talking to a hardware engineer that will help me make a bldc driver based on the Duet2 1.03 github files and the code is written in C++ right?

    I have a software engineer friend that can help me and another hardware engineer to help me do the firmware if the gentleman I am paying is only giving me the microprocessor code and not helping me configure your fork of reprapfirmware.

    If you remember talking to me about this months ago, maybe over a year ago (I think originally on the reprap forum) then this should sound familiar. I tried to learn enough about motors and firmware to do this entirely on my own. After however long it has been, I have learned how little I truly know. Since that discussion however long ago, I have developed a tremendous amount of respect for what you guys have done to get the Duet to where it is. I realized that doing this myself is unrealistic so I am paying a hardware engineer that has agreed to help me do this. I intend on only making about half a dozen of them and will post the files up when I receive everything from the hardware engineer. I was not originally going to openly say that I am doing this, I am simply because you were the one to respond.

    I intend on being able to use servo amplifiers similar to how steppers can use external stepper drivers. I told the guy to allow me to use encoders similar to these or the optical style. I told him that I didn't need the SD, LCD, and GPIO/50 pin header and that I needed at least 5 drives, with a Z-axis that could be powered by two as well if needed. He said it would take him about 4 weeks and he is doing it in Altium because of the library support. He knows Altium, not KiCAD. I was working with the cards I had. Am I wrong to think that the servo amplifier will be the tailored device for the motors? I have Nema 23 three-phase brushless motors (sensorless) with hall effect sensors on each phase measuring back EMF and since it should detect the edge of each pole…I believe it would act as an incremental encoder that would allow for positioning as well as rotor position. I am assuming 5v signal. I told the hardware/electrical/electronic/power electronics engineer that I wanted to use both the Faulhaber motors as well as the cheap Nema 23 BLDC.

    MicroMo (The Faulhaber Group) agreed to donate motors to this project of mine because this should open the door to laser cutters, waterjets, mills, routers, and metal printers.

    I do not know if it will remain in the same physical footprint. I probably should ask. I am also going to update the connector/headers because the ones that are on my Duet Wifi 1.01 are no longer sold from Digikey so I am going to use something more modern and lockable, I am thinking of the ones similar to the ones in PC's and are keyed so a child could do it....because I might use them for a class for kids. I am also probably going to use a USB Type-C connector so I can use a magnetic connector so I do not have to worry about and port wear. Using these motors means I can realistically think of a motor that is small enough and strong enough to be a direct drive motor for a Kossel and you said it yourself brushless as an extruder motor would be beneficial.

    I admit....I am a bit crazy. There is a method to my madness and I am thinking by doing this it opens up a lot of doors. 🙂

    Faulhaber motors are very expensive, I am not promoting them nor am I suggesting anyone purchase them. I have access to these motors completely free of charge. If the board can also be used with less expensive brushless motors...then it is a win in my book. I need a machine that can compete with the best additive manufacturing machines on the planet for my prototypes so I am using the resource available to me that is this motor company. I am not starting a company, not selling them for profit, I am just building a few for myself and will post the files when I get them. 🙂

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