Thread: Ballscrew Thickness!
Ok I've had a rethink, Have you already got your steppers and drivers yet?
If not then the better drivers have micro stepping. if you get the correct size motor then u can direct drive it and use the micro stepping to get the accuracy/ resolution you need.
Give gary a ring. Im sure he will help you and is much better qualified then me. Im just trying to cover all possibilities to help you make the right decision.
I'd agree with Ross - the drivers I got (from Gary) will do from 400 steps/revolution to 10,000. With a 25mm pitch, it equates to 0.0025mm accuracy.
Assuming I've divided it right (it's late...)
Remember though, every time you increase microsteps you decrease torque.
.John S -
hmmm ive already got the drives and motors from kelling in the states, the motors and drives are the 425 oz-in motor and KL-4030 Bipolar Driver the drive features are ..
* Voltage up to 24 to 40VDC, current output up to 3.0 A
* Selectable resolutions, 1,1/2, 1/4, 1/8, 1/16, 1/32, 1/64
* Suitable for 4,6,8 lead motors
* DIP switch current setting:
* Over voltage, heat and short-circuit protection
If i did end up gearing the ballscrew with some kind of belt and belt grip was a issue i could devise some sort of roller bearings in between the two pulley wheels so it would wrap the belt more so around the small drive pulley! just a thought, i suppose that all depends on what hight the teeth were on the pulleys and belt.
I think you need to come to accept realistic terms with what you have.
Running large 25mm screws at high speed with these motors and drives isn't going to happen.
You have a 6 volt motor that to accelerate up to speed is expecting to see 6 x 20 volts or around 100 to 120 volts and you only have a 40 volt max supply that is really only going to be happy on about 32 to 35 volts to stay inside a decent safety factor.
Gearing up, then micro stepping will only bleed off available torque making the situation worse.
.John S -
Those motors and drivers will be way too small.
If you are going to spin a 2500mm x 25mm screw you need a large 34, and a good supply of volts.
Under the speed you need those motors will most likly be only giving about 1Nm, also the inertia mismatch is way to large, even if you gear it.
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hmmm, ok guys what motors would you recommend to spin a 1900mm of 25mm ballscrew? would you go stepper or servo? and what drives would you suggest using?
It depends on how fast you want it to spin (and therefore how deep your pockets are).
I've used the PM2278 stepper controller, and the SY85STH156-4208 motor, which is about the most powerful combination (my philosophy is that it's easier to slow something down than to speed it up).
My steppers are running at 720RPM, which is about the fastest they can do. For more speed than this, then I'd need to go to servo motors instead.
However, my pockets aren't that deep - the cost of the three steppers and drivers was about the same ballpark figure as for a single servo and servo driver (so you're looking at three times the cost).
If I need the extra speed, then I'll upgrade, but for the moment it's fast enough.
What kind of speeds do you want?
If you want speeds like Tribbles has, you are on the border line of servo /stepper.
The setup he has is the SY86STH156 and the PM2278 run with 110V AC. (If i remember right)
With this setup you are looking at about £250 per axis, and you will most likely need two ball screws on X or it can crab, even with profiled rail.
A servo system will be about twice this, but will be far more accurate and much more responsive.
Our servo systems have 2500 line encoders that are quadrature so you get 10000 pulses per rev, and these are actual encoder positions rather than extrapolated positions that you get with an open loop stepper system.
With a servo system then the actual backlash of the mechanical system becomes the weak spot rather than the accuracy of the motor.
Donít forget with a servo system, you will need to gear it, and also consider the max frequency of Mach/parallel port, as this will be a factor in your max speed.
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ok, so if i get my self 3x PM2278 Drivers 2x 1810 oz-in NEMA 34 steppers for the X axis and 1x for the Y and use the NEMA23 for say the Z for the time being i should be able so work at a half decent pace and it will get the 6x4 table in motion? ive got no chance of going for servos at this stage!
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