Stepper Upgrades?


(mikep) #1

Has anyone found a benefit to a stepper upgrade to higher torque NEMA 23 steppers? I’m thinking about 350oz-in just to get a higher rapid speed.


(Dan Nelson) #2

I’ve thought about it, specifically for Z to add a screw drive, but I don’t know what the board itself will handle(honestly I’m pretty naive about these things). I was just about to ask the same question though so I’m interested in hearing what feedback you get. If I come across anything on my own I’ll be sure and post it.

Thanks,

Dan


(mikep) #3

They drivers do at least 2A of current, and I’ve seen some 340oz steppers that are 1.8A, so should work. Should as in the math works…


(Dan Nelson) #4

Math sounds good, I wonder about constant load and sudden peaks. Again I’m not even a “pre-novice” when it comes to such things. I mean I can wire a light switch, but much beyond that I’m not too well versed. I wonder if pushing a circuit up near its max for a prolonged period, which I’m thinking would induce heat, would eventually blow a driver? I mean my motorcycle red lines at something like 12,500 RPMs, but it doesn’t mean I could hold it at that speed for 2-3 hours at a time without causing some damage…it’d be fun while it lasted though!!!

Thanks,

Dan


(Daniel Loughmiller) #5

Why would you need more torque for rapids?


(mikep) #6

My understanding is that the frequency can be higher, acceleration can be higher, if more torque is available. According to the stepper selector over at geckodrive anyway. Haven’t figured out if I can increase the frequency yet.


(Daniel Loughmiller) #7

I wouldn’t be convinced it’s torque limited until I tried it, there seems to be a decent amount of torque available for cutting so rapids should be easy.


(mikep) #8

I’m asking because I want to know if anyone else has been down this little rat hole with some good tips to share.

Chamnit says 100khz is achievable. At ~40 steps/mm, that’s 2500 mm/sec as max feed out of GRBL. But, acceleration isn’t instantaneous (if you go from 1 step/sec to 100k steps/sec with no acceleration, you’ll just skip steps.) Probably also means pulse length might need to be decreased to get there (which is also a whole can of worms). Default acceleration (for shapeoko3 config) in each axis is 400mm/sec. which means at 6+ seconds of acceleration is required to get to 2500mm/sec from 0. In little 5-6 inch rapids, you’re probably not getting more than 200-300mm/sec (remember, it needs to accelerate and decelerate, and there’s not much time there)

If I increase acceleration (say, to 1000mm/sec), I get steps skipped. Yes, tried it. More torque should mean that acceleration value can be greater. How much more? 2000mm/sec? 3000mm/sec? I don’t know. Easier to find that one experimentally than my-awefully-rusty-calculus can calculate.

Clearly higher acceleration = more time at max speed = faster rapid, and you want that acceleration as high as you can get it without skipping steps.

Of course, all of that’s going to put some higher forces on the frame, so will have to see how that works out, it may make it all totally pointless, but don’t know till you try…


(Phil Thien) #9

I thought I read once that, upgrading to larger motors would actually reduce rapids?


(William Adams) #10

Yes, so long as one doesn’t get caught up in the problem of “The Wonderful One-Hoss Shay”

(and I say that as a guy whose first driver had a body from a company which started out making horse-drawn carriages)


#11

A lot of things are involved besides the rated torque of the motor, including the driver capabilities, inertia of the motor, inductance of the motor coils, inertia of the driven system, friction, gearing, and so on. There is no general rule, but changing ONLY the motor without consideration of the rest of the system likely won’t give great return.


(mikep) #12

Here’s the wiki discussion, has some useful bits:

https://www.shapeoko.com/wiki/index.php/Stepper_Motors

If it’s anything like the last time I did this to a carbide machine, it’ll be largely pointless, but a fun project.:slight_smile:


(Luke) #13

Did anything happen with this?

I’m considering it as an upgrade option, I’m not suggesting it’s needed? I imagine I’d need to add drivers to run say a 425oz motor…


(mikep) #14

I put it off for a while. Yes, you’ll need new drivers, which in turn pretty much means you’ll need a new controller depending on how frankensteined you’re willing to go (there are a lot of grbl options), and power. There’s a slipperly slope here for sure. It would be pretty easy to upgrade yourself to the point you would be better off with a used professional machine.

I did a Z upgrade a few weeks ago, that seems to have scratched my upgrade itch for the moment :slight_smile:


(Luke) #15

I appreciate you would need need new drivers to run heavier motors, but why change the control board. Is it because the existing board has drivers built in and a driver can’t feed into another driver?

Very slippery slope… I’m waiting on a replacement power adapter so whilst I cannot make anything my mind wanders…


(William Adams) #16

The board, like pretty much everything else in the machine is balanced to all the other parts — for the board, it’s the voltage and amperage supplied to the motors — AIUI, larger motors would want more current, so you’d need bigger stepper drivers.

See: http://www.panucatt.com/product_p/gm1pro.htm for one example


(Luke) #17

I get that bit, I’m not knocking it. The S3 board has it’s own drivers built in for up to 2a. Can you feed the S3 board into another set of drivers to beef up the motors in theory?

The current motors are rated at 2a, 127oz, but you could swap them out for say these ones which are 170oz 2a without making any changes to the board or adding drivers - granted I have no idea if it would make any difference…


(mikep) #18

Feed to another board: Not easily. You would need to solder on a bunch of wires, probably desolder the existing drivers, it would be quite a hack job. There are no connectors for this. There are other GRBL boards built for exactly this though, which makes the task easier for cheap.

Regarding the 170oz steppers. Depends. If they are like other Chinesium they may not actually be 170 oz., or may draw more than 2A. Then again, might be totally ok. For 15 pounds, you’re not getting yourself an high quality stepper to begin with. Might be ok, might be pretty much what we’ve already got.


(William Adams) #19

All good points.

I guess the way to phrase this is:

Are there any motors available which would offer a marked improvement on those which are bundled with the SO3 which would work with the existing electronics? If so, from where, at what cost?

One thing which I think would be worth looking into is 400-step motors — while one roughly halves the force needed to push the machine off by a step, one has more torque for a given size step (and unfortunately, one can’t change the stepping to 4x) — it would double the precision though, which for some applications might be worthwhile. This would be a good reason for the higher torque motor (if genuinely available in 24V 2A motors)