Replacing steppers for more torque options / Advice wanted - Page 3

1. ## Re: Replacing steppers for more torque options / Advice wanted

Hi DAAD - What is the width of the drive belt? Peter

2. ## Re: Replacing steppers for more torque options / Advice wanted

We use the work energy method in our design model. We wanted to harness the stepper motor's high torque at low speed to get to our desired cut velocity.
This video explains it
https://www.loom.com/share/64ef8fb13...006761e222b076

So by using smarter drives from Lam technology, we can reduce the current when torque is not needed. This gives the motors time to cool so then they do not miss steps as they no longer overheats.
But you can't harness those features if you can't determine constant velocity and have enough output pins to communicate with the drives in real time.
We use Linuxcnc and our custom component to do this 1000 times a second.

3. ## Re: Replacing steppers for more torque options / Advice wanted

I still am puzzled why posters quote stepper motor oz-in/N-cm by quoting a NEMA size?
NEMA 23 is a stepper motor with a 2.3×2.3 inch (58.4×58.5 mm) faceplate
My Vexta catalogue shows 9 steppers motors from 38.2N-cm to 132N-cm, ALL with the NEMA 23 mounting base size.

4. ## Re: Replacing steppers for more torque options / Advice wanted

Hello DAAD - I redid the calcs. I downloaded the drive file and it uses a 1/2" belt. Since I had the pulley geometry I used that to calculate the rotational inertias. So in summary. The drive system has been well designed as the motor torques and motor speeds match quite well for an accel of 0.83m/s/s and a top speed of 25m/min. So not talking about cutting at the moment, the motor runs out of puff at about 1000rpm and at about 968rpm it runs out of torque to accelerate the system. Again check the math. This is for moving the gantry as it has two motors. The Z axis being lighter will have more potential but its about half the mass and half the torque so its about the same...

The rotational side of things the motor is 96% of the inertia, the pulleys are 4%. So the math's for the system look good so its then up to the system to do the right thing. This points at the voltage again letting it down.... Keep at it. Peter

I just noticed that I halved the torque requirement for two motors, Shouldn't have done that as the calc was for one motor and one pulley system. But rotational component small so not wrong by much... won't correct it too many numbers for today. Peter

5. ## Re: Replacing steppers for more torque options / Advice wanted

found this readable article on stepper motor control Peter

https://www.edn.com/improving-curren...otion-quality/

6. ## Re: Replacing steppers for more torque options / Advice wanted

Hi DAAD - I was wondering about the 10N used for the friction in the AVID data so checked it out. I'm assuming here that you have 20mm rails. I looked up a car static capacity and used the graphs supplied by PMI. Other makers are about the same. I used a luggage scale to measure the seal static friction, its less once on the move and these are new cars so the seals are a bit sticky. Friction for the gantry comes out at 27N so 10N maybe a bit light. But its tiny vs the rest of the loads... Peter

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