Faster motors with less gearing?

There has been some talk about changing gearing ratios or screws to speed up the x/y motion. Another option may be a drop in replacement motor which is still unipolar but is less geared down.

RS seems to stock this series of 5V unipolar steppers with different gearing:

Does anyone who knows more about stepper motors know if these would work with the Sangaboard?

Note that if you put in the RS stock numbers into the website every version claims to have 7.5 degree steps. But RS is consistently rubbish putting correct specs on their website.

I think those particular ones are the next size up, so would be hard to drop in. They look to be 42mm diameter instead of ~27mm. Adafruit have the same 28BYJ-48 motors but with different gearing, 1/16 instead of 1/64. The same part number for different gearing is confusing, and their product page does say that they were 1/64 gearing for a bit in 2021!

I have spent a little time working on the gearing that we add between the motor and the actuator. We can easily make that 1:1 instead of 2:1. Going further to 1:2 is a bit more challenging, you can go quite a long way on x and y with everything in the same place but some changes to the order of the cut-outs, but not so easily on z. I think that the branch variable_gear_ratio does not have all of my musings recorded, that just makes the different ratio cogs themselves, whether or not they fit.

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I think it makes sense to have different gearing for x/y to z anyway?

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Definitely makes sense for xy steps to be bigger and faster (they already are by about 1.4x due to levers). For some applications larger motors would be fine if they’re available (though there’s then the question of whether NEMA is a better option).

A friend showed me a direct drive version that he wasn’t allowed to share openly because it was done on company time. That would be a neat way to gain a factor of 2, especially if it simplified the mechanism at the same time.

I believe it’s also quite feasible to get similar steppers with lead screws, but it’s then not a standard part and ends up being distributed centrally… Changing the gear ratio is a temptingly convenient option, especially for lower magnification work.

For gearing there is a merge request Draft: Choice of gear ratios for motorised microscopes (!352) · Merge requests · OpenFlexure / openflexure-microscope · GitLab. That just builds the different gears, and gains a factor of a little more than 2 on x-y. I also did some investigation of how to change the cut-outs to give more on z as well, and go further than 0.8:1 on x-y, on a local branch. I should put that on a merge request into the gears branch.

Ultimately working out a way to do direct drive with NEMA8 is the way to speed, but would probably need thermal management.

But I suppose we get a factor of 4 without changing the same body if we reverse the gear ratio?

I think @WilliamW tested that and concluded a factor of 2 was OK (1:1 gearing) but much more than that and you don’t have enough torque.

It’s an open question whether direct drive might be more (or less) efficient than 1:1 gearing I guess.

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One would expect direct drive to be more efficient, especially as the 3D printed gears will have a fair amount of play and friction. I suppose M4 direct drive may work and would give a small speed up above M3 direct drive?

it’s also easier to source for a lot of people, I believe - so yes, I think M4 direct drive would be a good option.

These NEMA 8s underdriven at 5V with relatively low RMS currents are working for me without melting their PLA+ mounts (yet). I’m not using them to drive flexures so perhaps that would require more torque.

Of course, they are much more expensive.

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