Stepper Torque Help?

[jbeuckm]

Hello - this is my first post on this excellent forum.

Here is my in-progress machine: Joe Beuckman » CNC Part 2

My steppers are marked 4v/.95A/1.8deg and I am suffering from unusably low torque. I changed the sliding aluminum channels to skate ball bearings and still have problems. If I am very careful with alignment and grease, I can get reliable slow motion or intermittent 600hz steps. I have been using EasyDriver control boards from sparkfun.com at full step / 30V and I am convinced that they can not supply enough current to utilize these motors well. But I am also wondering if these motors are too small to move this size of a table.

Could I use a controller like the Chromation unipolar kit with these Sanyo Denki motors? What would be the advantages of using a Gecko controller with my current or some other bipolar motors?

I would like to be able to etch PCBs, carve wood and etch shallow labels into aluminum panels.

Thank you,
Joe

[Hyrum R]

Someone with more electronics experience would need to confirm this for me. But I'm sure those motors would be way better off with much higher than 30v. They'd probably be happy with around 80v. However, your driver board probably couldn't handle it.

When I switched from a Xylotex driver board to the Gecko G540 and a 48v power supply, it was the difference of night and day with how my motors ran. I was always having problems with resonance at certain speeds, and the motors would suddenly stall for no reason at all.

I'm guessing those motors would like a higher voltage then even a G540 could give them. If you wanted some decent performance, I'd buy the motors that CNCRouterparts sells and a Gecko G540. Their motors are matched quite well to the specs of the G540, and you'd have excellent results.

Edit: Those motors you are looking at may be cheap, and that's exactly what they are. Round body motors are not recommended. I think it had something to do with losing their magnetism after a while or something. Plus, those are only .18 amps. Very, very wimpy little motors. Spend some money once and get a gecko, and I promise you'll never, ever, regret it. As someone else mentioned, the poor can't afford to be poor.

[hemsworthlad]

I'll second that opinion about Gecko's, and compard to your setup the differance wont be night & day but more like coming from totally blind to 20/20 eagle vision with 100X zoom. . Lol

I've found thru experience it's false economy trying to use cheap components, very often it cost's more in the long run and you get an under performing machine at best, at worst you go bald pulling hair out wasteing hours/days/month's of valuable cutting time that you could have used making stuff which you could have sold and payed for the whole machine 2 times over.

Sell what you have cutting your lose's the best you can and then like Hyrum says buy a decent G540 package, even if it means waiting weeks while you save the extra money it will be weeks well spent and reward you 10 fold.

With the G540 It will also go with you as the machine grows and you upgrade, which just about every one does, Even with a major upgrade or new machine build it will work fine for most of the nema 23 range motors with only a few of the larger sizes going past the 3.5A limit of the G540.

Mostly hassle free and you wont regret it 110% guarantee you.

Edit: Oh yes your problem if you havent figured is the wimpy motor Amp's.! In general Amp's equate's to torque and volts to speed so 0.95amps is a bit weak also like Hyrum pointed out @30v you are also way down on volts. For a rough ballpark figure for best performance work on 20x motors rated voltage.

[ger21]

As these guys said.

Basically, the less you try to spend, the more it's going to cost in the long run.

While I'll agree that the G540 is the best way to go, it is possible to do it a little cheaper.
I personally get pretty good performance with my Xylotex. However, I may be in the minority. And you must follow a few rules.
1) you need dual shaft steppers with good dampers, to remove resonance.
2) You need screws with 4 turns/inch or less, to keep motor rpm low.
3) You can't make any wiring mistakes, or it'll die.

A HobbyCNC package should also give you pretty good performance for the price.

But, the G540 is capable of double the performance of either of them, for not much more money.

Your call.

I'd recommend 200 oz motors or more, btw. Looks like the ones you have are between 60-100oz-in.

[JD_Mortal]

To me, they look like Nema-17 form-factor motor, and your specs for the motors operating power suggest that you need more beef.

4.0v x 0.95a = 3.8w

3.8 watts = 0.005 hp
0.005 hp x 12 IPS screw = 0.061 hp (Barely adequate)


If you drive them with 16v (4v x 4) at 1/4 step, that is the same as 4v average. You will only hear lots of musical vibrations as the "Amps" are not there.

I suggest, for that setup, you look for motors that are in the 2-3 amp range, with a specified voltage of 2-3 volts. You will want to drive them with 24-36v using a 6-9 amp power supply at minimum, with 1/2 - 1/4 steps.

Find a nema-23 form-factor motor.

Motor specs, 3.0v x 3.0a = 9 watts (Cool running, rated value.)
36v / 4 = 9v (Constant inductive average)
9v x 3a = 27w consumed (Hot running, but safe.)

9 watts = 0.012 hp
0.012 hp x 12 IPS screw = 0.144 hp (Adequate)

27 watts = 0.036 hp
0.036 hp x 12 IPS screw = 0.435 hp (More than adequate)

Have you tried longer pulse-times... perhaps your pulses are too short, and the motor coils are not powering up before switching-over to the next coils. Also, be sure you have tuned the motors for speed-levels. Motors have a minimum and maximum RPM. The minimum RPM is determined by the starting-voltage. The maximum RPM is mostly determined by the motors magnet-memory within the coil-plates. (If you are below or above your RPM limits, you will not have much driving power. Either the voltage is not enough to push it to the next stage, or the resonant magnetic fields are working against the next phase coil.)

Besides the motors, you are using a long drive nut, which may be manufactured "tight" for gripping power. Can you easily turn the nut on the screws? You might want to clean the grease off, and remove any metal burrs that may have built-up in the fresh grease. WD-40 the nuts, and clean them out good with a cloth. Use a wire-brush to clean thread gunk off the screws. Re-grease, and run it through full travel, several times. Take note where it seems to be sticking. The teeth may be damaged, but they will eventually wear loose. You could use a fine file to "fix" burrs which protrude off the drive-screw, which may be grabbing at the long threaded nut.

Also, try graphite, (Dry grease, pencil lead.) as your lubricant.

If you are only doing PCB... you might be able to use "formed plastic nuts". (Heat the screw with a torch, and clamp two halves of plastic around it. That forms a perfect threaded screw. Once it cools, it should shrink off the screw, and allow it to turn freely.)

I would stay away from any "kits" that do not include specs of any kind... What voltage limits, what amperage, what consumption is the board, is it optically isolated, is it protected form motor-surges?

For that same price, you can get a china-board that is sufficient for that size table. Motors will still cost you about as much as the board on e-bay. Just keep an eye on the motor specs. Remember amps X volts = watts, and (4x volts = safe, at the same amps), (10x volts = safe with cooling, micro-stepping max, at the same amps)

Amps is determined by the wire-thickness or AWG inside the coils. 3-ohms to 6-ohms is typical per coil. Volts is irrelevant, and is only listed as the "normal" or "dissipation", or "cool", or "rated" specs for the motor. You could run it at 100,000 volts if you ran it at 1/32 steps and didn't go over the amperage rating. Typically, the wattage is critical when heat-removal is not possible, and full-steps are your only option.

[hemsworthlad]

English version:
Buy decent bi-polar drive's IE: Gecko's use nema23 motors to suit machine size with PSU rated roughly 20x rated voltage and Amp's approx 70% of total number motors used. . . . . buy an optoisolted BOB with charge pump(If not using G540) wire together and start cutting. . . . It's that SIMPLE.. . No BS or heat problems.

Oh . . . Dump the threaded rod if you want any kind of speed or accurecy.!

[jbeuckm]

These responses more than answer my questions. I wish I would have been reading this forum instead of the instructables website where I started. Although, I do think that the easy-looking instructables articles served as a great bait-and-switch getting me into CNC.

Hyrum & ger21: I'm 110% convinced that the G540 is the best option for a controller and I'm saving for that. I burned out my EasyDriver testing beyond its rated 30V. Lesson learned, luckily for $15.

JD_Mortal: Thanks for the comparisons - very helpful to a beginner. Since my motors were marginally operating on about half their rated current, I'm going to try to get by with them for this "educational prototype" by running at full current when the G540 comes. If it's reasonably accurate but too weak to cut, maybe I'll mount my 7W laser diode and move on to the bigger machine.
I think the long nut turns easily enough, maybe not as easily as drive nuts that are made for doing this, esp. acme. The main holdup is probably that my couplings to the motors aren't perfectly coaxial so some binding is occurring. Also, I understand why to use dry lubricants now.

hemsworthlad: 20xV/70%I seems like a great rule of thumb. I would be interested in a discussion of drive methods. Are you saying drop rods altogether or just swap my home depot rods for acme? Maybe there's a forum thread where these things are contrasted?

I think this machine is salvagable as a learner, and I plan to get it operating for the experience, and then build a better one. There are a lot of great looking designs on this forum and I think the most difficult problem of all will be balancing my make-believe requirements with my real-life budget.

[hemsworthlad]

Originally Posted by jbeuckm hemsworthlad: 20xV/70%I seems like a great rule of thumb. I would be interested in a discussion of drive methods. Are you saying drop rods altogether or just swap my home depot rods for acme? Maybe there's a forum thread where these things are contrasted?

Hi,

Threaded rod is ok for learning the principles etc but it's not the most accurate due to the way it's made with often the pitch changing along it's length completly blowing any chance of repeatabilty or accrecy, the small pitch also resticts speed.

Acme is far better in both respects and not overly expensive. If you need any kind of repeatabilty and accurecy then sooner or later you will want to be upgrading to ACME or better.!

[stk2008]

Trapezoidal (is that ACME? don't think it is) I find to be a good though it gets no where near ball screw etc but then cost 1/4 of the price.

[CarveOne]

Originally Posted by stk2008 Trapezoidal (is that ACME? don't think it is) I find to be a good though it gets no where near ball screw etc but then cost 1/4 of the price.

ACME is trapezoidal thread rods. They have a flat top thread design. They come in many thread pitches, diameters, and multi-start threads.

CarveOne

[ger21]

Trapezoidal is a metric screw similar to acme. Acme threads are 29°, and I think trapezoidal are 30°

[stk2008]

Originally Posted by ger21 Trapezoidal is a metric screw similar to acme. Acme threads are 29°, and I think trapezoidal are 30°

Hi ger21 that's what I thought knew there was a minor difference and now you mentioned it yes it was the slight angle of the threads.