Upgrading pr control box

[jseiler]

I have a pr32. It has ball screws (.2 lead) on all axes and an old PR control box. It used to run on a 12V PC supply which I upgraded to a 28V supply. That helped a lot and got me up to a reliable .7in/second.

From what I have found in the archives, the PRT and PR are very similar in pulse rate per second (4000-7000 pps), the PR box operates in 1/2 step mode and the PRT is defaulted to 1/4 step. The stepping can be changed on the PRT control box, is that right?

So I should be able to (theoretically) assume I can get 4000 pps, which should be 4000/200*4*5 or 1 in/second minimum. If I change to 1/2 step with a prt control box, I should be able to get 2 in/second, assuming the minumum 4000 pps. Is that right? If I can get 6000pps, I could bet 1.5 in/sec in 1/4 step mode or 3 in/sec in 1/2 step mode, assuming my motors will have the torque at that speeed to make everything go.

So I think my current unit values are 2000, with the 1/4 prt box, they'd go to 4000, if I can change to 1/2 step, the unit value would be 2000.

The big questions are...will swapping the PR box for the PRT box work and can you change the stepping on the PRT box?

John

[jseiler]

Where is the documentation for the PRT control box? It used to be on the website, but I can't seem to find it.

[jseiler]

Anyone? Bill????

[Brady Watson]

What kind of documentation, John? What info do you need?

-B

[jseiler]

1) changing step size
2) number of pulses per second possible
3) wiring diagrams
4) maximum supply current and how to modify it to lower values for smaller motors
5) is there a prt control box manual that has this information in it that I can download?

John

[Brady Watson]

1) You can change step size between 1/4 & 1/2 stepping by toggling it on the board. There is either a dip swtich or jumper depending on the board model. Look for it, as it should be labeled on the board itself.
2) Max PPS on a PRT is around 25,000 PPS if you have good communication. Around 35k to 40K PPS if running an Alpha due to a faster/better controller. I believe the latest PRSAlpha now exceeds what a parallel port can deliver, 45k PPS+ via USB.
3) There are no wiring diagrams available for public view that I am aware of. The board itself is pretty straight forward. Follow the traces.
4) Max current to each motor is about 1.5A, but I believe the chip is rated up to 2A. You can swap out current set resistors (at each channel) if you want to monkey with currect reduction. I don't think that you would need to, and it would only be if the smaller motor was getting too hot.
5) Not that I am aware of, other than inputs/output & motor wiring. Nothing on the board level.

As as side note, the 4G is a much better choice for modified machines and custom applications. The drivers are better, configurable and the CPU is faster and has better communication components than the PRT board. Modifying a regular PRT board is not for the faint of heart, as some things require scratching off traces and other 'board ruining' activities to get it to be a poor man's 4G board, or otherwise useable board for custom applications. I've run Nema17 and 23 smaller motors on a regular PRT board with no problems. Others have as well.

I could be of more help if you described what you are doing in more detail.

-B

[jseiler]

My pr32 has ballscrews on all three axes at .2" thread pitch and pk266-02a motors. When the bought the beast, it was kind of a mess. Came with a 233 mhz laptop, old pr controls running off the internal 12v supply, and various mechanical issues. I fixed the mechanical stuff and got it moving. I replaced the 12v supply with the monster 28V alstom and this really helped. I limited to 2A with a 680 ohm resistor. I upgraded the computer to a 800mhz pentium 3. I'm about to take delivery of a prt box. I couldn't find any information about these boxes on the website, and what was on the forum indicated the maximum pps rate on these PRT boxes was in the neighborhood of 6000 pps. That meant chaning from 1/4 step default mode to 1/2 step. I believe my old box runs half step.

Depending on the number of pps I can get, I'm hoping to drive to 2-3in/sec on all axes (instead of the .9 in/s I'm getting now). I'm willing to swap out motors if it will help. I have some keling motors to try.

I'm thinking bipolar series if I can get the speed out of them at 1.5A.

pk 266-02a motor spec:
http://catalog.orientalmotor.com/item/stepping-motors--1068/pk-series-stepping-motors/pk266-02a

spec for possible on hand replacement.
http://www.kelinginc.net/KL23H256-21-8B.pdf

If I really can get 20000 pps out of the controller, I can run 1/4 step mode which works out to 25 revolutions/second. With 5 revolution/inch ballscrews, that works out to a ripping fast 5in/sec. I'd cry tears of joy to see my old beast move like that.

Am I crazy or is this really possible using a standard prt control box? After reading your post, I have a lot more hope.


(as a side project, I'm looking at using another prt box to run a minimill, but I need to play with the box on the pr32 first. There a suprising number of prt boxes out there for experimentation, but lets leave that one alone for the time being).

John

[Brady Watson]

John,
The biggest bear is the 5:1 screws you have. In simple terms, your max speed *could be* 3.6 / 5 * 5 IPS - I'll explain. 1/4 stepping a PRT with 44v PS will move a max of 5 IPS with 3.6:1 motors & 25T pinion. If we divide 3.6 by 5 (your screw ratio) we get: .72 & multiply by a max of 5 IPS, we get 3.6 IPS max Jog speed for your setup. So cutting speeds might be in the 2 IPS range. Having never run a PRT in 1/2 step mode, I don't know if your speed values will directly translate to exactly twice the performance....that's one I'd say to try out and let us know.

The Kelling stepper looks like it has about 18X the torque of the Oriental motor you picked out. If you run in series, you will sacrifice a little bit of speed and torque, but be able to run the motor nonetheless.

Nothing influences speed more than voltage. I would encourage you to put together your own toroid power supply or use a PRT supply calibrated for up to 48v. The 28v PS is really limiting what your speed could be (not sure if you are going to use that PS with PRT box or not)

-B

[jseiler]

2 ips real deal cutting speed would make me pretty happy. Most of the time I run .7 ips right now. 3x speed increase would make my day. I think you dropped a decimal point in there someplace (18x vs 1.8x).

I think the 1/2 step vs 1/4 step will be important depending on where my limitations are. If I'm limited by pulse rate, then 1/2 stepping would help a lot. If I'm limited by motor torque at speed, not so much.

How sure are you that a PRT control will run 20000 pps? Is there a trick to communicating with the prt control box that quickly? Will an 800MHz PIII still run things well?

The PRT box I'm looking at comes with the 44V power supply so that's what I'll use.

thanks tons,
John

[Brady Watson]

John,
I mistakenly took Oriental's Inch/Pounds for Inch/Ounces...So it looks like the Kelling is has about 10% more torque than the Oriental, but I would get the Oriental over the Kelling since Oriental is proven and doesn't make junk.

While messing around with the 4G development (essentially a hacked Alpha board with Geckos), I was told that the PRT controller was good to around 25,000 KBps communication speed. You should email them to verify that my memory is still serving me correctly. You should be fine communicating thru your regular serial port with a PRT box. I believe that the com speed limit is a function of the communication chips on the PRT board and the CPU (the card that sticks up on the board) - The Alphas are a lot beefier to deal with the increased processing and communication speed needed to run at high speeds. I think that you're going to have either a choice of speed (@1/2 step) or resolution (@1/4 step). You may find that the 1/2 step is too coarse as this would be like having the resolution of the 2.5:1 screw.

Going forward you might consider buying a 4G bare board and adding your own Gecko servo drives and a couple of servos from Kelling. That would make that thing run like a rocket.

-B

[jseiler]

My memory was off. I think the archive was saying that the max out of a PR box was 4000-7000 pps (depending on good communications).

Checking this thread, 25000 should be right. Mike R. is 99.9% right about these things.


http://www.talkshopbot.com/forum/messages/26/18313.html

Right now, I believe my old pr box runs in half step mode. So 1 revolution has 400 steps and each revolution is .2" or .0005" resolution. This is more than good enough, I think.

I like the idea of buying a prt box because it does give me an upgrade path to 4g instead of my original plan of going Mach/gecko straightaway. I really like shopbot control language a lot.

Have you seen mariss F.'s announcement about PID/feedback steppers he's working on? He mentioned it on cnczone. 40% more torque, no lost steps, all while maintaining 3 axis synchronization. I hope shopbot comes up with a version 5 or 4g+ version when mariss releases.

John

[jseiler]

My plans have changed for the time being. I really need to figure out 1/4, 1/2 and full step adjustments.

I am taking ownership of a k2cnc kt-1414 (14"x14") frame that I want to connect the prt box up to. I got the prt box working with the keling motors I have with the unit values set up appropriate to the k2 (.1" lead, so 10 turns of the screws/inch of travel). I connected up the motors in bipolar half coil (using only the a a/ and b and b/ coils) to keep the current requirements down while keeping the inductance reasonable (1/2 of the series bipolar and twice the parralell). Is it wiser to use only half the rated current in parallel bipolar to get the lower inductance or is it better to use half coil and run full rated current?

So...anyone have a clue how to set the jumpers on the prt board to get 1/2 or full step instead of 1/4 step? I can't find this anywhere in the manual, but it alludes the to the possibility. I'd like the option of the additional speed considering the 10:1 ratio on those k2 standard screws.

John