Stepper, torque, volts, pps

Hi all

Trying to make some sense of this
Objective : maximize torque and rpm and validate my (mis)conceptions
Application is non reprap

Motor :wantai nema 23, type 57byg621 torque curve attached

[www.wantmotor.com]

Max torque, 12.5 kg cm at 24 V, half step
Halfstep gives 40% more torque than full step, but some say 4988 enegizes both coils at full step too, but can't find it in the spec sheets-confirmation would be great

Typical power supply is 12V so torque=50%?
If a gearbox is used, for torque multplication, this often needs an increase in rps, to keep speed, this increases pps, torque is reduced -high pps drops torque ?-see attached torque curve(also efficiency of gearbox costs up to 50%)

Possible solution:increase volts to max 25 times (according to Gecko) the rated voltage, say max 45/48 volt? (using DRV driver instead of pololu) Driver amps set to motor amps in spec sheet . Motor will run hot. This doubles torque?? (Almost) but assume that BEMF becomes an issue-considering to use L6470 driver for compensation

If microstepping is used, torque as total remains the same, just divided per microstep?
But microstepping increases pps, so lower torque again-as per curve?


Appreciate your help in this

Coolerooney

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Typical power supply is 12V so torque=50%?

Same torque at standstill, but the torque loss due to speed kicks in earlier.

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Objective : maximize torque and rpm

You should have clearer numbers. How many RPM are required, how much torque is sufficient? "maximize" means using 480V, 4A and water cooling (to compensate for the over-current).

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Hi Traumflug

i want to know if the whole torque curve is reduced with 50% when voltage is reduced withe same %

To be realistic 480 volts , 4A is a bit OTT, as said, max is about 25x rated voltage, with this motor about 100V, but driver can do as stated max 45V so that is the practical limit
The built in charge pump in the L6470 can compensate for BEMF (partly)

The point is that rpm (rps) and pps are linked, therefore you can reach corner speed very quickly when you start microstepping-right? As per my original question

So if we do a simple 200 step/revolution, accoording to the torque curve we start to loose torque over 800pps, 4 rps- direct drive with 8 teeth T5 pulley yields 160 mm travel/sec
At >5000 pps, torque is about 25% of peak

Looking for 300mm/sec, =8 rps/ 1600 pps so my options are bigger motor or higher voltage
Microstepping again makes this worse?


Appreciate if you comment on my other questions

Thx

Coolerooney

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you can reach corner speed very quickly when you start microstepping-right?

Microstepping doesn't help in acceleration at all, as it doesn't increase torque. You just need more steps for the same speed.

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At >5000 pps, torque is about 25% of peak

But you need 1600 pps only, so you're far above these 25%. And yes, to increase torque at higher speeds, you need more voltage.

I have the impression you make too much a headache about the issue. There's plenty of experience, so you can safely assume a standard configuration works. And you can always increase voltage (within the stepper driver limits) later.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Hi Traumflug

Don't really understand your reply

Corner speed is the point of the torque curve where there is a sharp drop off in torque

Have no headaches, trying make sense of it-as said in my first line of my thread
Matching a stepper to a driver to an application is not simple

As stated, this is not a reprap application, so the experience is not very well documented

Coolerooney