Stepper or Servos?

[gavztheouch]

Im retrofitting my router with some new drives and motors. The old drives and control software is nearly 20 years old, so im looking to update my system to take advantage of the new software available, ie mach 3.

The old control system uses 2.9NM (continuous) DC servo motors at a high voltage 110V. Most drives use will work with voltages upto 80V for example Gecko drives and Granite devices. So if I stick with the motors im going to need a new power supply which runs at 75-80V and at least 1000w, Plus a new drive which is all going to add up, I estimate £400+ per Axis. I also don't know for sure what condition the motors are in as I have not owned the machine in a working condition or seen it working.

So im wondering if Im better opting for a Stepper motor system, Motion Control here in the UK have a 12NM Stepper System for under £300!

12NM is this going to be powerfull enough? My Servos are 2.9NM but this is continuous and not peak. How do stepper torque rating compare with servos?

Looking at my machine do you think Steppers will be strong enough? The gantry is around ~400KG

[gavztheouch]

I Found a bit of info regarding the torque.

Servos have between 5-10 times there continuous torque in reserve so my servos at worst are rated 14.5NM and best 29NM in comparison to Steppers.

Stepper also lose torque as they spin at higher speeds so as the gantry accelerates the motor becomes weaker? This might mean I would have to run the router at slow speeds.

[MrWild]

plus you would lose real time positioning. If a servo loses steps (can't keep up) the drive faults and E stops. With the steppers, if steps are lost, the part is scrap and you only find out when you notice the out of spec part.

I you reuse the old servos, you will also need to fit encoders. If your drives are good along with everything else, you could fit encoders to the servos, and run a MESA 5i20 board with EMC2 as the control.

[Al_The_Man]

That looks like a fairly large machine, especially with 400Kg Gantry, presumably the motors could handle it with the old system, do you know what the specs were on the old Machine?
The largest demand on the servo's is going to depend on what accel/decel rate you are looking for.
They appear to be SEM motors, if you use them, you can disconnect the Tach's.
due to modern drives operate in the torque mode.
I don't believe these motors were very high speed, so if you do any gearing, you may have to work with an estimate of a max of around 2000rpm.
Al.

[gavztheouch]

Its a hobby machine so speed is not so much of an issue, I plan to use it mainly as 2D profile cutter.

One rev of the motor seems to move the X and Y about 30mm, so at 2000rpm thats 1m/sec.

The encoders where not mounted on the motors so i've had to remove the caps and make some brackets to mount them.

The DRC encoders have two channels A+/A- and B+/B- I have powered them up with 5v and watched the output on a multimeter. The voltage moves up and down as the encoder is revolved, Im assuming they work but I will hook them up to an osilloscope once they are mounted on the motors.

Im thinking of using Granite devices for the Servo drives and making a power supply capable of powering the two from one supply. Can anyone recommend my a supplier in the UK or elsewhere that will deliver to the UK?

Cheers
Gav