Converting to +/-10v Possible?

[simonrafferty]

I have a Bridgeport Interact with a dead servo drive. A replacement is going to cost me best part of $1000 and the one that has blown was replaced with a 'reconditioned' drive 12 months ago - so I'm not keen to buy another!

Gecko's amongst others are fairly inexpensive and capable of driving the 100v/15A motors - but they have step / direction control. It seems that you can get a good quality S/D drive for $150, but +/-10v start at about $1000 for DC motors.

I'm wondering if, by using a microcontroller I can convert one to the other?
The +/-10v controls the velocity with feedback from a tacho generator. The uController can read the voltage with a simple ADC and use the tacho to generate the step / direction pulses as required.

The offset (programmed on my TNC 370) can be controlled by the uC as can the servo lag by increasing and decreasing the number of pulses per sec for a given ADC voltage.

Have I missed something? Is such a converter already available or are there low cost +/-10v drives around that I've not found yet?

Si

[Al_The_Man]

I use AMC http://www.a-m-c.com/ they have a wide range of analogue drives, also if using a DC motor, their BLDC versions work just as well with DC motors, if the PID loop is closed back to the controller, then you do not need the 'intelligent' type drives.
Ebay is a good source, but I am not sure if you have as many available in the UK.
Also Copley Controls and Aerotech are another couple of makes.
Al.

[simonrafferty]

Thanks Al,
Unfortunately, in Europe there is almost nothing listed on eBay. There are several companies selling apparently re-conditioned drives but as I've found, they are very expensive and rubbish. Having wasted nearly $4000 keeping the machine's electronics going - I feel the time has come to draw a line under it and go with something more modern.

The drive that blew was made in 1991. I suppose I wouldn't expect a 20 year old TV to be reliable - so why should a drive.

Since a Gecko drive is only $120, even if it requires a microcontroller and some development - at least at the end of it I've got something modern that should last a few years and even if the rest of the electronics dies, I can convert to Mach3 fairly easily.

If a suitable driver comes my way for sensible money, I'll try it - but I need a decent fall-back position for when the next and the next fail! Has anyone done anything like this before? Should I just dump the TNC 370 and go for Mach3? (or something else?).

Although this forum is going to be biased towards Gecko's, and they are probably the best known - are they the best option for a mill this big?

Sorry for the number of questions!

Si

[TOTALLYRC]

I think US Digital makes a device that does what you want.

http://usdigital.com/products/interf...nverters/epot/

Not sure if it is exactly what you want but maybe they can help.

Mike

[simonrafferty]

Fantastic!

That's exactly what I was hoping for!

It will potentially be useful for others as well since one of these + a Step Dir servo controller are about $250 compared with $500 for the original drive.

Thanks very much,

Si

[TOTALLYRC]

Originally Posted by simonrafferty Fantastic! That's exactly what I was hoping for! It will potentially be useful for others as well since one of these + a Step Dir servo controller are about $250 compared with $500 for the original drive. Thanks very much, Si

Glad to help.
I am looking at it to add a small stepper driven 4th axis to my machine that doesn't have step and direction output. For the cost I could just change to a servo motor and drive but we will see. Please post if you get one and it works out for you.

Mike

[simonrafferty]

That's an idea too!
I have all the wiring for 4th & 5th Axis - but no servo drivers. I also have a nice indexing head that could easily grow a stepper motor. Then just run it without closed loop positioning except for an end stop and I would have a 4th axis!

Si