Bridgeport Series II R2E4 Boss 9

16 May 2018 23:29 #110797 by tightmopedman9
After waiting almost a year for a suitable retrofit candidate to replace my Sharp with 2 axis Prototrak, a Series II R2E4 popped up on CL. The machine is in practically new condition, and was only run as a backup machine to another R2E4 before being sold to someone who used the machine for less than 1 hour in 7 years.

The machine hadn't been turned on in 6 months prior to me looking at it; shortly after booting the machine started drawing enough current to almost stall a 3HP phase converter. After much head scratching and no easy solution the asking price was dropped $1000 and I had it delivered to my shop.

I found that one of the smoothing caps in the power drive circuit was a dead short, so I removed it to test the machine. I wasn't able to get the axis limit warning to disappear until I jumpered the last item in the e-stop/axis limit chain, a relay named CR1 with an unknown (to me) function. As soon as I did this I was able to home the machine, but the motion was extremely jerky. I turned the machine off and grabbed my scope to look at the quality of the DC power with the missing cap. Without the servos on there was less than 50mv of ripple. The X and Z axes were the only ones that moved during the homing procedure, and now the DCS board (a subsection of the servo amp) on both of these axes displays an overcurrent fault.

I purchased a new set of servo amps for cheap on e-bay, but unfortunately the DCS boards are listed as Series I only, which I assume had smaller servos, so I'm not sure if they will work. I would like to keep the original servo amps to save money, but I'm not confident I'll be able to get them to work now.

I've been considering my options if I can't get the stock servo amps working. Ideally, I'd like to have LinuxCNC close the servo loop, so I want to avoid step/dir drives. I'd like to keep the cost of this retrofit fairly low, so I'd like to spend less than $200 per amp if possible. The servos are MT30R4-33, rated at 3.2NM stall torque, 4000 RPM max speed and 65A max. I can't find a datasheet for these servos specifically, but based on the datasheet for the other MT30R4 servos I'd guess the continuous current is about 11A.

I've been looking at Copley and AMC drives, but I'm having a hard time finding a drive that would be an ideal canidate. From the factory, the servo drive voltage is 128V, which gives a rapid of 250IPM. The AMC 30A8 seems like a popular drive, but is limited to 80V. The Copley 422 seems like another popular drive, and can handle a supply voltage of up to 180V, but can only provide 20A peak. Would that be enough current? Or should I sacrifice rapid speed for more current? Does max speed scale linearly as a function of voltage? Would the 250IPM @ 128V scale to 156IPM @ 80V?

I'll update this thread when I receive and test the new servo amps boards.

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18 May 2018 21:53 #110856 by andypugh
I am guessing the machine has DC servos?

The Mesa 7i29 might be an option for the servo drive. Integrates well with other Mesa cards (obviously)

Current = force and voltage = speed, approximately. But 20A @ 128V is 2.5kW, that's plenty of power and I think will be adequate.

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18 May 2018 22:56 #110864 by tightmopedman9
Yes, brushed DC servos.

I replaced the DCS boards this afternoon and was able to get all axes to home. Unfortunately the motion on the x and y was very erratic, I'm assuming the velocity loop on the new boards needs to be re-tuned.

I decided I don't want to deal with the hassle and clutter of retaining the stock servo amps so I purchased 3 x AMC 30A8 amps. If I find the rapid speed to be lacking I'll look into a higher voltage amp, the 30A8s were less than 250 for all 3.

I also placed an order for a 6i25/7i77 and an ASRock q1900b, 4gb ram and 120gb SSD.

I'll start putting stuff together next week and probably come back with some questions.

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24 May 2018 16:31 #111090 by NCPatrol
I just bought this machine a couple months ago:

Kind of an older version of your machine, but very similar. In the case of my machine, the PO started with using the original steppers but ditched them for new servos after a year or so. Might be some useful info in that thread for you.

I still don't have a clue what I'm doing with it...just getting in to learning the CAM side of things.

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