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CNC Stepper motor speed limits

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tcmtech

Banned
Most Helpful Member
My brother just got his home built 3 axis CNC table built but he has one rather limiting problem. Stepper speed limit.

His top travel speed is only 15 inches a minute! The stepper motors he is using are these.

Vexta PK266-01A-C23
2 PH 1.8 /STEP
7.4 Volt 1 Amp


The control boards use TA8435H driver IC's
He has a power supply capapble of 0-40 volts at 15 amps so power is not a problem.
Everything moves smooth and works well but the motor RPM's just seem low. If they get over a specific speed they have problems.
Is there a way to get more RPM's out of them or will he just have to change the mechanical drive sytem?

I have seen stepper motors of this size and step ratio run at much higher RPM's before.
 

mneary

New Member
One of the most important things to do is to use a high voltage with current limiting. It looks like the TA8435H takes care of this.

The second very important thing is to ramp the motor acceleration rather than abruptly starting it. This takes into account the available power for the mass that needs to be accelerated. Is his control firmware doing this?
 

Belphgor

New Member
What program does he use to run the g-code? Is he missing steps? Closed or open loop? Is that his rapid (G0). Are the axis binding?
 

bryan1

Well-Known Member
Hi TCM,
With the movement going so slow could be the pitch of the driving thread is too fine and are the steppers directly hooked to the drive screws or coupled via a sprocket or timing belt? 15" a minute is slower than a snail on heat so something is way out of wack. Also any chance of some pic's of the cnc unit and the drive arrangement could throw a light on whats wrong.

Cheers Bryan
 

tcmtech

Banned
Most Helpful Member
He has his ramp up and down times correct and the motors top out at the same stepping rate even when not hooked up to anything.

I will have to ask again what program he has. but I do know its a better one.
He does computer work for a living so its not a software hack job!

As far as system friction the drive screws are direct drive and can easily be turned by hand. perhaps a few inchounces at most. Its all bal bearings on every moveing component.

Its just that no matter what way he changes the stepper drive peramiters there is just a top limit on speed before they start stumbling and getting glitchy.
And as I said before I know I have seen stepper motors underload run many times faster than these do with no load.
 
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