Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: randol on June 04, 2008, 04:12:01 PM
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Hello all. I've been running Mach for almost two years now on a Taig mill and I love it. I recently decided to attempt a build for a small, high precision lathe using Kollmorgen ServoDisc motors. The motors are equipped with a tach and an encoder currently. They are low torque motors which is acceptable for the setup. My question is: will a basic L298 based driver work with this setup or will a feedback loop be necessary on the servo driver?
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Dont know anything about the L298 so maybe you know all this already and I am answering your question wrongly. However servos need feedback or they wont work, If they are DC then without feedback they would just be like ordinary DC motors in that there is no way of accurately controlling their position. If they are AC servos then you will also need commutation signals to the drive so that they can drive the motors coils in the right sequence.
Hood
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As Hood says , you'll need a more intelligent controller made for servo motors , rather than stepper motors they work totaly differently , using the encoders for positional information , i'd leave the tacho's alone though , no good spoiling a good job half way through .
if you need a controller take a look at Kmotion from Dynomotion.com
if your up to wiring it in , you'll probably still need the actual fitted servo drives or you could use a snapamp
just my thoughts etc
dave
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Thanks for the input. The L298 is a chip for assembling a driver and I have yet to find out if it has feedback capability. I think I might end up assembling a couple of the UHU controllers and two of the L298 drivers for the axes in the end product. This is totally new territory for me as I am building the lathe from the ground up and all of the electronics on the side. It's a rather ambitious undertaking but hey why not. Dave: what did you mean by spoiling a good job half way through with the tachs?
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the l298's dont have any feedback , they are very basic driver chips , if you have shaft encoders fitted then you don't need to use Tach's , the encoders have better resolution , you then can have more modern controller's do most of the work .
Tacho's are mostly old hat and were used for older analog drive systems.
Dave
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If you are using motors that have Tachs then likely they are brush type Tachs. As Dave has said you will likely not use the Tachs so I would think it best to remove the brushes from them so that there is no chance of accidentaly causing a short with the wire ends.
Hood
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Thanks again for the info. The tachs are brushed and I have verified an output voltage when turned by hand. I'll have to take care of that prior to installation.