Will These Motors Be Good For An Upgrade?

[rb99]

I have an older machine that I put a new 4g box on. I saw these motors for sale locally and I am wondering if they would be suitable replacements:

Superior Electric Slo-syn Motor

Type: KLM091S-103

1.78VDC
4.67AMPS
200 Steps/Rev

[Brady Watson]

Those (http://ottawa.kijiji.ca/c-buy-and-sell-business-industrial-SloSyn-Stepper-Motor-W0QQAdIdZ382274480) motors are direct drive - meaning that you will only get about 1/3 the resolution of a PR or PRT with the factory 3.6:1 gearbox motors. The only way to really make them work without being disappointed, is to use belt reduction. The PK296A1A-SG3.6 motors used on PRTs are $257 ea, which are cheaper new than trying to get those used motors to work via belt reduction and they are no better than whatever motors you are running now (whether direct drive or gearbox motors). They appear to be the same physical frame size as those used on a PRT, including a 1/2" shaft. Sometimes there are ads on here for used motors.

-B

[rb99]

Cool...I am not going to get into anything more than just bolt on new motors.

They are brand new and the guy wants $50 each for them.

Thanks for the info.

[gerryv]

Richard, is your expectation then to purchase and install new motors that are good value but not expect any improvement in precision, etc?

[rb99]

Richard, is your expectation then to purchase and install new motors that are good value but not expect any improvement in precision, etc?

I have the older motors from the PR machine. They are ok but I think the newer steppers are better from a power and resolution perspective.

Also my shafts are bigger and the pinions are very expensive, (I think $40 each) plus there is no key-way to lock them, only the hex screw.

So if I could get some new motors cheap I would probably get them. These are selling for $50 each, and are new, or at least not used. Unfortunately they are not plug and play...and I am not about to build gearboxes.

[gerryv]

I've had a PRt alpha, PRS standard and now a PRs alpha but no PR so I'm afraid I can't offer much on that comparison. However, being a retired geezer with time on his hands I follow the forum a lot in the hopes of learning a little and it seems to me that the 4g upgrade and following Brady's insights into pinion gears give you the biggest bang for the buck with those machines. I spent a lot of time a couple of years ago looking into belt drives as a means of pushing my PRT to higher resolution and in the end felt that it was above my capabilities. I also felt at the time that if I'd had a standard rather than an alha, when all was said and done the best and easiest choice would have been to invest in new geared steppers. But, I'm no expert for sure so defer to those who know more.

[Brady Watson]

I don't see the logic in buying those motors. They will make your machine perform worse than it does now, or at best make it perform the same if you have direct drive motors. They will only work with a 4G or better board, or you will fry the electronics because they draw more than 2 amps. The SLoSyn motors + Geckos will give you 2000 microsteps per 1 revolution of the motor. The original PR Vexta motors with 3.6:1 gearboxes built into them will give you 7200 microsteps per 1 revolution of the motor shaft - the Vextas can resolve 3.6 times finer detail than the SloSyn motors. Just keep that in mind.

The shaft size on both the PR Vexta motors and the SloSyn motors are the same - 1/2". I do not know if the SloSyn has a keyway on the motor - most likely it does not. If it does, you would need a custom pinion broached and keyed to match the keyed shaft. SB never offered a motor with both a 1/2" shaft and keyway. If it has a keyway, it is most likely a 12mm shaft motor - Standard or Alpha. Right now, you can order pinion gears for under $20 a piece from McMaster that will match up with your 3/8" rack - the only mod that you would want to do is to drill & tap another grub screw hole 90 degrees to the one they give you to match up with the flats on your Vexta motors. This is super easy, and I do this when I need to replace pinions on a 3/8" rack'd machine using a drill press.

The next thing to consider is that the PR is a great machine in stock trim running at speeds it was designed to go. Once you start adding more speed, you quickly start to see how flimsy the frame components are from the added forces of acceleration and deceleration - so you'll want to add some gussets and braces in the appropriate places to beef things up. A stock PR with a 4G upgrade can get a bit 'wally' when you get over 4IPS & the 45 degree v-roller to unistrut 'rails' - so don't be fooled. What many people have done to beef up the rails is to move to a PRT style vertical rail, and rotate the v-roller round 'bars' 45 degrees to make the X car ride like a PRT.

I'd hate to see you buy those motors and be disappointed with the results. Stepper motors, especially the Vextas are very reliable and running on a PR with a low voltage power supply, makes them even more attractive since they were barely breaking a sweat on a slow stock PR. They are really good motors - a much better choice than the SloSyn ones, especially if they have gearboxes on them. Also, since the SloSyn motors draw over 2 amps, you would need to change the current set resistor on each Gecko in the 4G control box, plus add a heat sink to each driver or you will have an overheating condition, where the Geckos would shut down while cutting to protect themselves.

The hot ticket for a PR is to use the stock motors and a 4G upgrade control box with a 48v power supply. It is the path of least resistance, and the best performance bang for the buck. If you keep speeds reasonable, it will be a fantastic tool. If you want more speed than say 4IPS while cutting, then you really have to ditch the PR hardware and move up to a PRT style frame and gantry. The PR may physically be capable of going over 4IPS, but once you apply cutting forces, it isn't pretty. There are guys out there running over 4IPS on a PR in production - but you really have to keep the machine in tune & the unistrut the v-rollers ride on wears out way faster the faster you run the machine....Things to consider.

What is the goal of going to the other motors - to gain speed, resolution, torque? What type of machining do you want to do with it that you can't do now?

-B

[rb99]

Wow stepper motor school! Thanks for the great info.

I did not know about the motors, and saw that they are selling for $50 each. So if they would have been the perfect motors (which I see now they are not) for $200 I could have gotten a fresh set of motors. But that's not happening.

I think the shafts on my motors have some play...When powered up I can move the shaft back and forth. I have found it hard to get the pinions super tight on the shaft as well. Also the pinions need replacing I think. Can you tell me what I am looking for from McMaster?

It has been a few years since I did any real work on the machine other than cut square sign blanks out (with nice radius corners). But yesterday I finally installed the 4g box I bought new in 2009, and it works pretty good. My table is pretty heavy duty, and it is about 12' x 5.5' cutting area.

Today I bought a 12" Shopbot Z off eBay, so I am hoping to get some really descent quality and speed out of my cutter. The old ball screw Z, the low power and the accuracy kept me from digging in. I think that cutting at 4"'/sec. will keep me happy. I would like to do 3d carvings and signs. Perhaps do custom work for carpenters.