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Why does Maslow have its own custom shield?

#1

Just curious… why does Maslow need/choose its own custom-designed shield? Wouldn’t a commonplace, off-the-shelf CNC shield (like RAMPS, for instance) be tried, tested, and cheaper/easier?

Is it to do with extra power required to haul a router around vertically, or the different coordinate math, or something like that?

#2

I suspect someone else will have more detail. The motors we use are closed loop, motor, gear box, & encoder. Ramps is designed with stepper drivers, a diffrent motor (stepper motors) that is open loop. It has no facility to work with the encoders.

These are just a few reasons. More exist and probably get expanded on.

Thank you

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#3

Interesting. My (limited) understanding on that topic is that CNC machines normally use stepper motors, which generally don’t need encoders for accuracy, as opposed to servos, which do, and that stepper motors are usually high torque at low speed, but low torque at high speed. I guess Maslow needs high motor speeds for the distance it has to cover, plus high torque for the weight it’s shifting, and so had to switch to servos, then add encoders to get the accuracy back?

#4

its a cost thing. You would need some monsterous steppers to move a router like that, and then they would be too big for the RAMPS foards etc anyway. With the current design, it uses DC motors which is way cheaper fro the size load they can carry. They then have a big worm drive on them which means you cant back drive it, which is handy for a big heavy load. Then also with the encoder, you probably (dont actually know the numbers, but assuming here)get more resolution anyway, so can actually be more precise than a stepper as well. Plus closed loop is better than steppers anyway… and servos that size cost a million dollars (they don’t, but you get the idea)

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#5

The Maslow uses DC brush motors, a different technology from steppers, entirely. Too, the Maslow motors have a worm-gear gearbox to reduce the speed and multiply the torque. Finally, the worm-gear arrangement means that when power is removed, the sled remains in the same position that the controller left it, so re-calibration isn’t needed with every power cycle. All together, a different approach to moving the cutting tool around.

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#6

Ahh. Thanks for the insight, @blurfl and @Ned. Lots of interesting details there that I didn’t know. Might even inform a little medical infusion pump project I’m toying with (though I expect that to be nothing usable for years), if I can use a small dc motor + encoder to save space and gain accuracy over small steppers.

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#7

no, the maslow needs more accuracy than steppers provide, along with lower
speeds and higher torque.

steppers are 200 steps/rev (400 for "high precision) steppers.

The Maslow has >8000 steps/rev and with the gearbox is very slow.

the Maslow motors are cheaper as well as having higher torque than available
steppers

but the reason for the Maslow custom shield is that it’s cheaper than anything
else available that can drive the DC motors.

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#8

In this application steppers could also be usable, the steppers could also drive a worm gear drive and be self locking. The output torque is a function or motor torque times the gear ratio. the big advantage is speed.

#9

once you add a worm gear to the steppers,and add stepper drivers, you now have added significantly to the cost.

by the way, NEMA 17 steppers are fairly cheap as they are used in so many 3d printers, but if you start looking for anything bigger or smaller, the price jumps quite a bit.