Why does my stepper motor stop rising when I make diagonal movements?

Thread Starter

alexsmith

Joined Sep 28, 2021
2
Hello, I am new to stepper motors and am having a problem.

I have a machine that operates in all three directions (X, Y and Z) and has motors.

When I do linear movements (one after another) everything goes well I reach a fairly high speed and I am able to lift my load.

However, when I want to combine these movements together (moving diagonally) my motors start to lift the load and made it almost halfway. After that, it is no longer able to support the load and the load is freefalling.

After some research I believe the problem is that the current is not strong enough to support more than one motor at a time at their operating speed. So I wanted to confirm if I should change my power supply and have a power supply unit with more voltage and current which increases the torque of the motors.

Thank you
 

Papabravo

Joined Feb 24, 2006
17,313
All the motors that you will ever see, besides all the ones that won't have the same problem. As you make them go faster they produce less torque. At some speed the torque may actually drop to zero and they will either stop or the load may be large enough to make them go in reverse, This is especially true for motion against gravity on the z-axis. All I can say is that you need to find an alternate strategy.
 

Irving

Joined Jan 30, 2016
2,322
power W = speed (rad/sec) * torque (Nm) so if all your motors share a common PSU its output power will govern the total torque-speed product. If your two motors cope with their task at a lower speed then you've confirmed that's the issue. Ideally you'd have a separate PSU for each motor - this is common in higher end CNC machines while low-end kit tends to have a shared supply and this sort of slew-rate limitation.
 
Last edited:

MrSalts

Joined Apr 2, 2020
738
Hello, I am new to stepper motors and am having a problem.

I have a machine that operates in all three directions (X, Y and Z) and has motors.

When I do linear movements (one after another) everything goes well I reach a fairly high speed and I am able to lift my load.

However, when I want to combine these movements together (moving diagonally) my motors start to lift the load and made it almost halfway. After that, it is no longer able to support the load and the load is freefalling.

After some research I believe the problem is that the current is not strong enough to support more than one motor at a time at their operating speed. So I wanted to confirm if I should change my power supply and have a power supply unit with more voltage and current which increases the torque of the motors.

Thank you
In most cases, just a higher current power supply will help you. No need for higher voltage because you'll also need more current as you increase the voltage (nature of ohms law, higher voltage will push more current if you have the same load (resistance of the motor).
If you have a large capacitor (1000uF to 10000uF of sufficient voltage rating, you can try putting that across your existing power supply. A capacitor will flatten the peaks and valleys of power demand. Worth a try if you have a larger capacitor but a higher current supply is a better option.
 

Thread Starter

alexsmith

Joined Sep 28, 2021
2
power W = speed (rad/sec) * torque (Nm) so if all your motors share a common PSU its output power will govern the total torque-speed product. If your two motors cope with their task at a lower speed then you've confirmed that's the issue. Ideally you'd have a separate PSU for each motor - this is common in higher end CNC machines while low-end kit tends to have a shared supply and this sort of slew-rate limitation.
Indeed my motors are able to do the same task at a lower speed !! Thank you, I'll by another PSU or a bigger one.
 

Irving

Joined Jan 30, 2016
2,322
Indeed my motors are able to do the same task at a lower speed !! Thank you, I'll by another PSU or a bigger one.
It would be better to have a separate PSU for each motor. If you want 1 PSU for all 3 axis then simply use the calculation:
PSU Watts output approx = 0.12 * ((rated rpm * rated torque)motor1 + (rated rpm * rated torque)motor2+ (rated rpm * rated torque)motor3)
 
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