Bridgeport CNC + EMC2, which output hardware?

I am planning on a conversion to EMC2 for my Bridgeport R2E4 CNC. It has Boss9 control which although it is fairly functional is finicky (hardware wise). The good thing is that the machine is already equipped with excellent servos and encoders as well as a host of power supplies, isolation componentry etc most of which can be reused. The servos are brushed and run on ~100V/10A.

I plan to rip out the BSP2, FDMC and video boards and replace with a PC/EMC2. My main question is how to do the PC to servo interface. From poking around the Mesa cards seem like one of the better options. The 7i20 should be able to do what I need.

From there though I need to decide how to drive the servos. The cheapest/simplest option (in theory) is to use the existing analog servo amps and just buy an analog output card for the Mesa (+-10V). I'm skeptical about this though since even apart from the terrible whining the amps put out I'm not sure how long they will last. I could also go with the analog output cards and buy surplus industrial servo amps (ebay etc) although it seems difficult to get a matched set unless you buy new which is very expensive. My last option is to buy some PWM output cards (like the 7i29 from Mesa or the Pico Systems PWM card) and drive the servos directly from the Mesa card with no analog output card. This may or may not be cheaper than the industrial amp route depending on how lucky I get on ebay.

Is there a preference amongst the EMC2 users between these options? Will I have any issues doing direct PWM control or is the +-10V velocity control a more tried solution?

Thanks!


James

I am a beginner - so take what I say with a grain of salt...

But check out what PWM scheme your drives expect - as it turns out mine didn't use PWM and Dir - they used %5 d/c as full backwards - %50 as stop - and %95 as full forward ...

So any DC source could pretty much read as 'go flat out' NOW - I think thats why they specified the offset of %5 so it might have worked out anyway, but I just didn't want any headaches so went with a 7i33 PWM (from the supported anything I/O cards) to analog interface ...

My gear would eventually be operating around people so the less dangerous situations to think about the better

Your gear probably wont be as finnicky as mine was with PWM

andypugh wrote:


There are a lot of successful Pico converted Bridgeports out there, Jon@pico has one himself.

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I just want to point out that email is wrong, my email is This email address is being protected from spambots. You need JavaScript enabled to view it.

If your servo amps take in a PWM signal, then the Pico Systems PWM controller could also be used.
It needs a slight variation in the HAL file settings to accommodate your scheme where 50% duty cycle
means "don't move".

Jon