Need Help Selecting Steppers

[forgetcolor]

I see it's a common question so forgive me for repeating it. I've read lots of threads but don't have a handle on how to make the choice.

I'm building a jgro. I'm using 1/2"-10 5-start screws. The heaviest load I'll be pushing with the gantry is a Bosch 1617 (~12 lbs.). I've read that bigger is better, smaller is better, etc. I'm planning on going with Gecko drives, although haven't narrowed it down yet. The motors from Keling look good and I was thinking about either their 425 oz. in. or 495 oz. in. nema-23 dual shaft steppers.

Can anyone give me some guidance?

thanks!
fg

[jschmitt]

I think those are pretty good choices. I would worry about being too big because you will most likely want to built another when you are done. I was thinking about my next two before I finished my first

If you want to engineer this, Phil Moore has a link: http://pminmo.com/PMinMOwiki/index.p...chanical_Power

this link worked this morning: http://zone.ni.com/devzone/cda/ph/p/id/223

[ger21]

Which Gecko drives are you planning on using? If using the G540, the 318oz and 387 oz motors will give you higher rpm's than the larger ones. To maximize the performance of the larger motors, they need to be run at higher voltages than the G540 can handle. Ideally, you'd want to use a G201,202, or 203 with those.

Having said that, there are plenty of people using the larger motors with acceptable results.

[forgetcolor]

Thanks to you both.

jschmitt, the first link helped me understand the relationship between stepper speed and torque. The second link relies on some figures I don't know yet, like the gantry weight. You're probably right that I'll build another down the road, but I'm not worried about spending a little extra on the first one if it gives me a benefit.

Gerry, to answer your question, I haven't figured it out yet, but I'm open to whatever works. I should note that I'm trying to maintain the ability to use my jgro for not only routing, but also for a custom art painting application. I know to make the latter work I'll need to also have some kind of control over a motor mechanism that will pickup/drop paint brushes. Because of this, I'm not sure if a 4-axis setup like the g540 is the right approach, because I'm guessing that treating the brush motor as an 'axis' isn't going to work.

It seems like it might be better to go with individual drives (e.g. the g201,202,203) for the axes, and then some other kind of drive/control for the brush motor. I don't quite understand how I can squeeze all of this through one parallel port yet. I must need some sort of BOB between the drives and the port? I plan to use emc2 as my software base and will modify the code (or write supplementary programs) as necessary.

I plan to get the cnc router app working first, then will adapt the design.

On motor size, it sounds like matching motor voltage with driver voltage is a key, otherwise I'm wasting the capability of the larger motors. If I go with the g201-203 so I could drive the larger motors at their intended voltage, will I get better (faster) performance? Or is it just as well to go with the smaller motors (e.g. 318/387 oz. in.)?

[ger21]

If I go with the g201-203 so I could drive the larger motors at their intended voltage, will I get better (faster) performance? Or is it just as well to go with the smaller motors (e.g. 318/387 oz. in.)?

Maybe, but I'm guessing maybe not. You may get quicker acceleration, though. You probably won't get higher velocities, though. "Faster performance" is a little vague. Typically, as the size of the motor increases, it's maximum rpm's will be lower. So if you plan on using them at their max rpm, then you may not be able to spin them as fast. But it's tricky, because if your talking about driving the smaller motors with a G540, then it's voltage limit may limit rpm's. If you're using a G201, for instance, with both motors, then most likely the smaller motor will spin a little faster. But to determine this, you'd need accurate torque curves of the motors, with the intended drives at the correct voltage. Not likely you'll find this info. I guess the answer is, if the smaller motors can deliver the performance you need, then go with them. To really answer this question, you need to have target velocities and accel rates in mind, and must do the calculations to find out how much you need.

[Crevice Reamer]

Bear in mind that the torque/speed curve given in the first link is for Bipolar Series wiring. The best wiring method for our purposes is usually BIPOLAR PARALLEL, which allows more torque at higher rpms.

I would choose the G540, which has a built in break out board.

CR.

[pminmo]

Bear in mind that the torque/speed curve given in the first link is for Bipolar Series wiring. The best wiring method for our purposes is usually BIPOLAR PARALLEL, which allows more torque at higher rpms.

CR.

The point of the article is for people to understand the mechanical aspect of motor power in linear motion. Too many people don't consider it's a combination of motor, power supply, rotary to linear conversion mechanics, efficiency, driver and software. The result is the spend money in places they don't need too. Severly over power axis that motor power isn't the problem. Over speed without realizing the mechanical downside. While your statement is true, the point of the graph is that steppers loose torque as they increase in speed. The shape changes, on drive methodology regardless of series, unipolar, parallel.

[forgetcolor]

I would choose the G540, which has a built in break out board.

CR.

CR, thanks for the suggestion. The G540 looks very attractive. What I don't quite understand about it, though, is how I would get an additional motor into the system. The three axes motors are easy. But I'll need some kind of motor for the paintbrush gripper. Can I run this through the 4th axis of the G540? Or is it common to get another LPT port and just run extra stuff through there?

Finally, if IIRC, the G540 voltages limits the size of motors I can buy, right (more so than, say, the G203v)?

[forgetcolor]

Someone on the EMC2 list just pointed out to me that the G540 has two 1A, 0-50VDC outputs and suggested I could possibly use these to operate a solenoid (or at least a relay that operates a solenoid) for my brush gripper. I presume there must be some way of getting access to this output in emc2.

Does this make sense?

I see that Keling has a kit with the G540, 387 oz. in. motors, and a 48V/7.3A power supply. Any reason this wouldn't be a good setup? My forum searches suggest this might be a good fit of motors with the g540. I'm also guessing that once I had the cables, this package would get my CNC application up and running pretty easily.

thanks!