Closed Loop steppers

**funkmonkey** · 17-07-2009

Help, I have 2 closed loop vexta stepper motors on a machine I have just bought. The machine has no drivers, I am looking for a 3 axis driver system, now can these closed loop steppers be run by a Bipolar or unipolar driver? or does it have to be a closed loop controller? I am not that bothered about the feedback system working as with the closed loop system, I just want to run the machine.

**Gary** · 17-07-2009

A closed loop stepper system consists of a stepper motor with an encoder either on the back of the motor or a linear encoder.
the closed loop would be handled by the controller not the driver.
you can use the motors as normal, you would just not connect the encoder.

**funkmonkey** · 17-07-2009

Ok thts great, mechanically this thing is sweet, just I have no idea what I need to buy to get it to running on the electrics side.

**funkmonkey** · 17-07-2009

This is the machine, I would like to get this running as a 3D router, any ideas on bits that are needed? Any help would be appreciated.

**irving2008** · 17-07-2009

Originally Posted by funkmonkey

This is the machine, I would like to get this running as a 3D router, any ideas on bits that are needed? Any help would be appreciated.

Not bad for £510... if you read off the part # on the motors or any other info we should be able to give you some clues!

**funkmonkey** · 17-07-2009

yeh I thought it was a good buy....when I picked it up today the guy said he paid £24 at auction for it, insolvency deal....thanks a lot I thought, didnt really need to know that!

x axis - VEXTA ASM66AK-T7.2 CLOSED LOOP STEP MOTOR
Y axis - VEXTA ASM66AK-T7.2 CLOSED LOOP STEP MOTOR
z axis - VEXTA PK266-02B 2 PHASE STEPPER MOTOR WITH CLEAN DAMPER

There are quite a few optical limit switches all over it.

**Gary** · 18-07-2009

It looks like the motors are 1.2Nm holding torque so with a ratio of 7.2 that would be about 8.6Nm of holding torque, so the actual torque running would be about 4-6Nm depending on the speed /voltage.
You are right, you will need to dump the existing X and Y motors because of the gearbox, not specifically because of the max speed but also because of the 45arc minutes of backlash and that the system uses belt and pulley so that 45 arc minutes would equate to quite a bit of movement.
I would personally use a mid sized 34 frame motor if you are going to continue using the existing belts or going to a 60mm diameter (3Nm) motor if converting to ball screw.
I would also consider reducing the height of the router to make in a bit more ridged.

**funkmonkey** · 18-07-2009

yeh I was going to chop a little out of the legs to get it closer to the deck to improve the stability, also the head does not move down any where near the base plate so it needs to drop down.

Thanks for the help you guys, so to recap:

Ditch the Vexta motors

Buy two new 34 frame motors

Drop the height of the x, y & z axis closer to the table

But what kit do I need to get this running? drivers, breakout etc?

**Gary** · 18-07-2009

Motors, Drivers, breakout board, power supply, pc and cnc contol software.

Originally Posted by funkmonkey

yeh I was going to chop a little out of the legs to get it closer to the deck to improve the stability, also the head does not move down any where near the base plate so it needs to drop down.

Thanks for the help you guys, so to recap:

Ditch the Vexta motors

Buy two new 34 frame motors

Drop the height of the x, y & z axis closer to the table

But what kit do I need to get this running? drivers, breakout etc?

**funkmonkey** · 18-07-2009

Ok, so is any better than others as there seems to be a lot about?

Also the software side, we use Machine Strat, Delcam & Bobcad here. Do the drivers need specific headers in the G-code text to run?