Upgrade Advice

[dighsx]

Well I feel I might be at a crossroads. I’m currently running a Xylotex controller and have started having some problems with it. (Before I go on I just want to say I’ve been happy with my Xylotex up until a few weeks ago. And their support has been fantastic. I don’t want anyone to think I’m putting their product down or bashing them)

All that said I’m wondering if it’s time I upgrade to something that could run things faster. Let me back up a bit and give some history to all this. Early last summer I build my first CNC machine (the Jrgo design) I thought about buying Gecko’s back then but I opted for the Xylotex because it was an out of the box solution and at that time I didn’t know if/how well my machine would work. Also I didn’t know if this was a hobby I was really going to get into or not. So I kept things simple. Here we are almost a year later and I’m starting to build my second machine, which of course will be about twice the size of my current machine. I had planed on just moving my motors to the new machine and use my current setup. But then I started having some problems with my Xylotex. In my search for a solution to my current controller problem I’ve started to realize that the Xylotex might be capping my motors/machines performance. (The Xylotex is capped at 27-30V max)

So here’s my question: I’m currently running the 269oz motors from Xylotex (http://www.xylotex.com/StepperMotor.htm) If I’m doing the math right these motors are 3.2v (rated current X phase resistance) I’m running at 26V which is only 8 times the rated voltage. If I got Gecko’s I would be able to run these at a higher voltage, which I think in theory would get me better performance and power. Is this true? Is this worth it? I run around 18-20ipm cutting and rapids around 26-28ipm. If I upgraded will I see a big gain. Also the new machine I’m building is bigger so more power to the motors be better?

Thanks

[fkaCarel]

I think your motors are on the small side. With a higher supply voltage you would get somewhat higher RPM. I would advice to look also into servo drives. You can tune and prod a stepper drive, but a stepper is at it's best when static. A servo is specified in volts/rpm. As firms like Gecko make 1 on 1 replacements considering puls and direction, it should'nt pose insurmountable problems. And no more missed steps. You can always build up experience by converting 1 axle.

Carel

[ger21]

Does your JGRO have 5/16-18 leadscrews? If so, you can probably triple your speed just by changing the screws to 1/2-8 2 start acme. Joe's machine, with 1/2-10 acme, a HobbyCNC and 200 oz motors can move at 80ipm, so you should be able to go quite a bit faster without switching to Geckos.


As a general rule of thumb, increasing the voltage will increase your top speed a proportional amount. Double the voltage, double the speed. But, you don't want to use too high a voltage, or your motors will get too hot. Somewhere between 15-20 times is probably best.

If your building a bigger machine, and switching to Gecko's, I'd recommend bigger motors too. Nema 34's with 400-600oz in of torque.

But, how fast do you want to go? What will you be cutting?

[dighsx]

I'm using 1/2-10 lead screws for my current machine and the new one. And my new machine is Joe's new design. So part of me thinks I could just stick with my current motors and move up to Geckos and a bigger power supply.

I've only cut wood, MDF and some corian and really don't have any plans for cutting anything else. Also I'd be happy with getting 30-40ipm cutting. I'm not looking to set any speed records.

If I could get my Xylotex to work reliably I'd build the new machine and see how things go before upgrading. But I'm on the hairy edge of not trusting it anymore.

So lets get down to brass tax, what's it going to cost me to upgrade to Geckos and bigger motors. I figure I'd have about $400 for the Gecko 202's. What will Nema 34's cost me. I'm assuming they'd be servo motors and not steppers? Servo motors are closed loop right? Which if, true would be a nice feature (if I understand how they work correctly). Also would I need to get a breakout board like the CNC4PC? I’d need a new power supply too; I’ve got the 24V one that came with the Xylotex but for a new setup that isn’t going to cut it.

One kind of advantage to upgrading would be that I could leave my current machine alone. So I'd have two machines if I can get my Xylotex problems figured out. And what's better then one cnc machine... Two cnc machines.

Thanks for the help.

[dighsx]

Here's a stupid question, if you could get a NEMA 34 769oz or a NEMA 34 1303oz motor and cost wasn't an issue would you get the bigger one? It seems to me like more power is never a bad thing, but....

[ger21]

It depends on the torque curves, and how fast you want to spin them. Usually the bigger ones will lose torque faster, and the smaller one may actually have more torque at higher speeds.

But, if your'e building Joes machine, the steppers you have may be fine, if run at 36-48Volts and Geckos.

[dighsx]

This is my current plan. Build a new power supply, get the Geckos and then try it with my current motors. If it seems like I need more power then upgrade the motors.

As the power supply goes, my current one is 24V 5A. Should the new one be more Amps? Seems like it should, but how much more? I was thinking 10A but that's just a stab in the dark.

The reason I asked about the bigger motors is I did a favor for a guy who sells motors and there is talk of getting me a deal on a set. So if it were some great buy I'd be a fool to pass it up. At least that's what I tried telling my wife....

Thanks for the help.

[dighsx]

Ok I might be able to get a really good deal (free) on these motors http://www.shinano.com/xampp/docs/SST83D.pdf (model STT38F3C011) If I can get these I figure I'll build a 48V 10A power supply and get the Gecko G202s. My gantry including router will weight about 61lbs. I'll be using 1/2-10 screws. My question is this, looking at the performance graph is there some formula to figure out how it'll do with this setup? I'm sure they'd be more then enough but I was just wondering how 'real' people figure out motor sizes.

Also I'm mainly be cutting wood, and corian. I could see doing a little AL cutting but not much.

Thanks