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https://www.faulhaber.com/fileadmin/Import/Media/EN_AM1524_FPS.pdf

I am using this motor with a 250:1 planetary gear drive, I am moving a mechanism that requires .3 inch pounds of force. The company says it will produce the required torque at 3.3vdc and only use .26amps, I am having problems with this giving me enough breakaway force to move the mechanism at temperatures of -40*. Right now the motor is set to 1/4 steps because I was under the assumption that it would produce more torque but, I had another individual that said a 256 step it would give me a more significant breakaway torque but at speed it would be less likely to produce the same torque.

I am not all that smart when it comes to this but, I am asking for your advice. The motor will only run 12 seconds from hard stop to hard stop and the accuracy isn't all that important due to the gearbox but I do need a good amount of torque when cold. Would 256 steps work better at cold vs 1/4 steps?

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  • \$\begingroup\$ First get yourself a chopping driver with a supply voltage several times the coil rated voltage... That said, at your temperature extreme many things likely get decidedly weird. \$\endgroup\$ – Chris Stratton Oct 21 '20 at 19:59
  • \$\begingroup\$ Does the mechanism need that much torque at -40C, or is that at room temperature? Things tend to seize up at cold temperatures. \$\endgroup\$ – TimWescott Oct 21 '20 at 20:18
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    \$\begingroup\$ Faulhaber is an excellent company, I would suggest asking them about performance changes at -40°C and below. \$\endgroup\$ – Spehro Pefhany Oct 21 '20 at 20:19
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    \$\begingroup\$ you could always energize the windings in a way that does not result in movement and let the motor warm up ..... or warm up the gearbox using a resistor \$\endgroup\$ – jsotola Oct 21 '20 at 20:19
  • \$\begingroup\$ the mechanism at a temperature of -40 is only .3 inch pounds its not mechanism. I am working with Faulhabuer to verify my settings but the EE we hired to design the board decide that 256 microsteps would give me less breakaway force and I think he is wrong. I also think he truncated the current to the motors instead of letting it pull what it needs mostly because the power supply he used only produces up to .6 amps. I am thinking micro steps to get it moving is better than trying to used full steps. I know that full steps are better at speed but it only runs 12 sec at a time. \$\endgroup\$ – bowen71 Oct 22 '20 at 13:34
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You would need a special oil the gearbox for that temperature. You can refill it by yourself, but you need the specification of the oil and the exact amount of it. And of course you would need to disassemble the gearbox and dump the lubricant, clean the gears and then reassemble and fill the new lubricant.

Also, make sure you use the correct stepper driver.

EDIT:

With increasing microstepping value the torque drops a quite lot and if the value is too great it could happen that the motor can’t produce enough torque to even turn. Usually 1/4, 1/8 or even 1/16 can produce satisfactory smooth movements while still producing enough torque. source

enter image description here

Note that when the current in phase A is at max, the current in phase B is zero when microstepping, meanwhile in full step mode each phase outputs the maximum current. So the output torque is smaller when using microstepping.

enter image description here

Let we have two currents: Phase A and Phase B that are geometrically shifted by 90 degrees. The depicted is a vector sum that has an absolute length of \$\sqrt{2} \cdot I_{phase}\$, this is how full stepping would look like. The position of the vector can only have 4 different positions for one electrical turn.

In microstepping these two phase currents are modulated, so that you get a rotating vector that has many positions. The currents do resemble a sine wave, so imagine these two vectors changing, so that the resultant vector draws a circle. It can be deducted, that a resultant vector has an absolute length that is for the factor \$\dfrac{1}{\sqrt{2}}\$ smaller than the previous vector length of the full step. Therefore the microsteping torque is only 70.7% of the full step torque.

enter image description here

It clearly says that the specified holding torque output is referred when both phases are ON - full stepping.

enter image description here

Your description is missing:

  • supply voltage
  • driver type and current setpoint
  • motor maximum speed

If the supply voltage isn't high enough, then the motor will stall as soon it will start to move. If the environment temperature is always such low, then you could increase the current above the nominal current. With some smart stepper drivers you have the ability even to set the motor current at zero speed, this would be practical for you - example: you set a small current at zero speed, and then a large current for moving. This setup would prevent burning your motor even if you accidentally start without having a motor cooled at -40 C.

Note that for a motor AM1524 0250 (Vn=3.5V, In=0.25A) you would need a supply voltage 12V to 15V, with current capability of at least 0.5A (theoretically). Practically you need more current, since the driver chopper has to be adjusted for 0.25A per phase, in this case the supply current is on its limit. If the torque isn't enough and you need to boost it, then you would need double current. I would start with 12V @1.5A.

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  • \$\begingroup\$ The motor is very small and the gearbox is equally small, it uses florocarbon gel that is good until -60c. The question was about stepping, I know that with the gearbox at speed the motor feels almost zero torque but the starting or breakaway torque required to get the momentum going is greater. My question would microstrepping give me a better start/breakaway force than full steps? \$\endgroup\$ – bowen71 Oct 22 '20 at 13:29
  • \$\begingroup\$ @bowen71 No, it wouldn't. The stepper motor, at zero speed can output a holding torque, which is the highest output torque for a given current. When it starts to move, then the torque begins to decrease until it reaches the knee point, then it goes rapidly down. This knee point is related to the motor voltage and motor's back EMF voltage. So you have to make sure that driver supply voltage is enough high and that it provides chopper current limit, which has to be set according to motor nominal current. \$\endgroup\$ – Marko Buršič Oct 23 '20 at 6:45
  • \$\begingroup\$ @bowen71 You didn't specify exactly which is your motor type, there are many different in that datasheet. What kind of stepper driver you do use, and what is the voltage supply of the stepper driver. \$\endgroup\$ – Marko Buršič Oct 23 '20 at 6:49

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