Servo drive recommendations for CNC update?

I have an old Supermax mill which has an Anilam Crusader II CNC control. I've been tinkering around finding out how to program basic moves, but I'm fully convinced that the best thing to do with it is to retire the old controller and upgrade it to LinuxCNC.

This weekend was the last straw as I was trying to tune the Z axis drive (the constant high pitch "singing" was drilling right through my head) with very little success and, in a moment of excessive haste I reconnected it the wrong way around. The singing stopped, but so did everything else on the drive, so I suspect I've blown a/some transistor(s) on the drive. I can't say I'm completely upset as I then found that the Y axis is also singing, but a good deal less noisily and I'm done with twiddling the tiny 20 turn potentiometers with little or no discernible benefit!

So, this decision now gives me the opportunity to replace the controller and drives. The controller decision is easy - a Mini-itx motherboard with LinuxCNC , a Mesa card and interface board.

However, I'm struggling with deciding on what to do about the servo drivers - the current setup has linear glass scales for positioning and they seem to be working fine & the servo motors have tachometers which feed back into the old drives. From what I've read online so far, it seems that this kind of feedback is outdated and what I now need to do is to pull out the tachometers and replace them with rotary encoders (US digital E5 or similar), sending the output from them back to LinuxCNC via the Mesa card, possibly using the linear scales as a calibration check/backlash eliminator.

So, what currently available DC (I'm going to keep the existing brushed servos - they seem fine) servo drives are recommended? The Granite Devices VSD-XE 160 seems good but a bit expensive and it seems to support every form of input. The Dugong, Viper & Gecko drives only seem to accept pulse/direction input which doesn't seem to sit well with LinuxCNC as it closes the loop in the drive rather than in LinuxCNC - or am I missing something here? If I were to get a Granite drive or other analogue drive would it need any feedback or control connections other than the +-10v?

Any help most welcome as I think I've been reading up on drives for a bit too long without getting far enough towards a solution!

Ben

Ok, thanks for the information guys - I hadn't spotted the Pico or the Mesa drives before, so they may well be an option.

The 7I29 is also interesting, but it works out very similar to the Granite as that can also be configured to control two axes.

Rather annoyingly, earlier this year I bought a Mesa 5I25 with a 7I77 & 7I76, with the intention of initially using the 7I77 to control the old analogue drives, then replace them with step/direction controlled drives further down the line. This was before I really understood the "correct" way of using LinuxCNC to close the loop (not to mention before I blew one of the old drives!). So, now I know a little more, it appears that I should've looked at PWM control for replacement drives, so a Mesa 785S would've been a better buy than the 7I76 - and at about half the price! I guess I'll just have to chalk that one up to experience - don't order anything until you've finished tinkering/learning/breaking bits.

On balance I think I'm going to hang onto my two working analogue drives - one of them is a more modern replacement which works quite nicely with no horrendous singing (screeching) coming from the servo when it's at rest - and use one for the Z axis, while getting new drives and powering the X & Y with them. That way I can get away with buying one Granite or Mesa drive and use it to drive both axes.

BJT - So you just reused your existing servos/tachos and drives exactly as they were when under Anilam control, but with the addition of rotary encoders on the servos? How did you go about mounting them? I've taken one of my servos apart and if I remove the tacho parts, then turn down the shaft to 10mm I should be able to fit a US Digital E5 in there perfectly. Assuming that I won't need the tachos on X or Y any more that's what I'll do, but I'm not putting anything in the lathe until I'm certain!

Ben

Moderator, what is the typical (?) motion control board or what ever that drives servo amps with the linuxcnc system.
looking to understand the device between the PC and Servo Amps, Servo amps are Mitsubushi or Yaskawa

Jim

Advanced motion controls makes very durable ,easy to set up amps. They are all over ebay and not real.expensive new. Your motors are probably around 90 volts,so something like a 25a20 will work fine. Amc amps can be set up to.run in velocity or current mode, so you can run with or with out tachs. Id keep the tachs if they work,current mode amps are a pain to tune. As for encoders, Accucoder makes good quality inexpensive encoders,which also show up on ebay......you can also mount them.to the end of the screw. Linear glass scales are known for their accuracy, might be worth the hassle to keep them.

JR1050 wrote:

Advanced motion controls makes very durable ,easy to set up amps. They are all over ebay and not real.expensive new. Your motors are probably around 90 volts,so something like a 25a20 will work fine. Amc amps can be set up to.run in velocity or current mode, so you can run with or with out tachs. Id keep the tachs if they work,current mode amps are a pain to tune. As for encoders, Accucoder makes good quality inexpensive encoders,which also show up on ebay......you can also mount them.to the end of the screw. Linear glass scales are known for their accuracy, might be worth the hassle to keep them.

AMC and Copley have many of the same models, not sure who makes them for whom.
Pico Systems (my company) makes an interface board set for analog velocity servo amps.
I agree with JR that velocity amps with tachs can give the smoothest performance.

We also have a product line with a digital controller and PWM servo amps that can be used
with DC brush motors.

One problem with glass scale encoders is the older ones have very low resolution. Also, I think
the Anilam scales are analog output, and you'd need to construct a comparator board to turn
them into digital signals.

Jon