Thread: Closed Loop steppers
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.
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.Visit Us: www.zappautomation.com
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.
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.
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.
The closed loop (X, Y) motors are going to be a little tricky. They are geared 7.2:1. According to the operating manual the standard driver for these does 0.05deg/pulse, i.e. 7200 pulses/rev, which means the motor does 1000 steps/rev, some form of microstepping drive. This is great for a very accurate pick n place mechanism but far too slow for a router. You may have to look at replacing these motors, but note they are offset (motor body to shaft) due to the gearbox. Might need a new bracket making up.
The Z motor is a fairly conventional 2-phase bipolar or unipolar motor. 1.4A phase (bipolr series)
Thanks, so what I need is a new pair of motors and a 3 axis driver kit to make this work properly?
Will flog the Vexta's off on ebay I think then. What size motor roughly do you think I will need for this machine?
No worries on making bits I have a 3,000 sq ft workshop filled with machines, so I am all good.
Last edited by irving2008; 17-07-2009 at 11:30 PM.
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.Visit Us: www.zappautomation.com
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