Max IPM Possible with Motor

[Sanghera]

Hi all,
I have a Xylotex 3 axis board and 3 190oz in Vexta Stepper Motors rated at about 2 amps for the way I wired them. I don't have a torque curve for the motors. I have been reaching speed of about 30IPM max with a 16TPI screw, then the motor stalls out. I am just wondering what the best size screw (TPI) would be for my machine to reach it's full potential in speed. I know that if you get a 5TPI ball screw you can get higher IPM, but you would need more torque to push it. What speeds are you guys out there reaching with similar sized motors?
Thanks.

[H500]

How did you wire them? What voltage are you using?

[fyffe555]

And what amps, is this uni, bipolar serial or bipolar parallel? whats your microstep setting, what are you driving it with (TCNC, Mach2 etc) and what's the load on the screw?

30ipm on a 16tpi screw is 480rpm, that's not too bad at all. It's definitely fast enough that you're torque has dropped off a lot from the motor rated maximum. If you're running the motor at less than rated V and A for your wiring you've probably got less than 25% of rated torque at that speed. You need to find the torque curve for this motor.

So, if it's load related you're loosing torque at speeds less than you'd like and the load imposed by the screw/nut/gantry is greater at that speed then the thing stalls. To speed it up look at reducing the load or giving the motors more power or lower tpi. I don't think its the Xylotex unless your wiring wrong, have too low A or V supply.

Another issue might (though its a very long shot) be step rate. 480rpm is still only 1600hz or 1600 steps per second full step or 12800 htz max even at 1/8 step. If your acceleration and max rate settings in your controller sw are *way* higher than that, try setting them to something you've calculated to match the speed you actually want to achieve. I had the same problem for a while until I realised I'd screwed up the Tcnc ini file.

FYI with a 3977 driver ( a mod version of Pmimno's - thanks phil ) on 2.5a and 28v, 1/4 step with a powermax II 118oz in bipolar parallel unloaded I can run it over 800rpm. On my small cnc machine (12x12" with 16tpi) I can get almost 60ipm. It seems to run better with load. Totally useless at this speed due to machine vibration from crappy bearings and screw whip. I run it at 30ipm max for circuit boards.

With a commercial driver ( IMS483) and powermaxII 240oz motor on another machine I can get over 1200rpm, 1/8 step at 4a and 48v. I run it at 600 rpm and 5tpi so get 120ipm and this is pushing a heavy gantry.

[Sanghera]

Hi, it is unipolar 2.9 amps 1.16ohms unipolar, 190oz-in unipolar. Using a 24VDC 10Amp Power Supply with the Xylotex 3 Axis board. I don't have a torque curve for the motor right now. Can I run the motors at their max amperage setting without hurting them, or should I stay on the safe side and run them a little bit lower (Bipolar Series). When you say "to speed it up look at reducing the load or giving the motors more power or lower tpi" how do I get this extra power from the motors? By using lower tpi? Can you elaborate a little if possible on the TCNC problem you had? Do you think it would be possible to reach speeds of 200IPM rapids with these motors. I looked at the hobbycnc site and he says that with 127oz-in motors and a 5TPI screw he can get +150IPM on his machine. I don't know if these motors have a very good torque curve or not, but I am just thinking if I can get similar speeds with these motors. The Xylotex can only handle 35V max I think and I may get a 28 VDC power supply. I don't really want to pay for a new CNC Electronics system.
Thanks.

[fyffe555]

The motors are rated 2.9a unipolar? so thats about 2a bipolar series and 4a bipolar parallel? You shouldn't exceed the rated Amps for each wiring scheme. How are yours wired? The Xylotex is a bipolar driver so you have the choice of series at 2a and parallel at 2.5a. Series would produce the most power at full rating for the motor in bipolar series. get a torque curve and see what that might be.

"to speed it up...." - the motors are staling at 30ipm? to increase this you either have to 'reduce the load' of the machine on the motors - that's friction, weight ( or inertia) of gantry and leadscrew, 'give the motors more power' - that's run the motors at thier maximum rated amps and high volts - you're limited by the combination of driver and motor specs, or 'lower tpi' - which is to say change the gearing of the machine. Less tpi, 10 instead of 16 say would mean the motor is turning slower for the same speed. Since steppers produce almost all thier power at low speeds you need to gear the machine to get the speed you want with the motor turning at the speeds its producing the power - just like a car.

The TCNC 'problem' was me being dumb, *not* Tcnc. I'd set acceleration rates and speeds in TCNC by mistake. Nothing was going to keep up and too many steps per second meant the motor lost steps and stalled. It's a usefull exercise to calculate your target ipm speeds, convert that to steps and put that into Tcnc and then adjust up or down in small steps until the machine misses or you get the speeds you want. Together with changing the microstepping it helps see what sort of resonance and stall speeds your machine has. For example, I've one machine thats a pig at 1/2 steps and smooth and way faster at 1/4stepping, everything else being the same.

200ipm rapids is pretty fast! Is your machine up to it? and do you really need it? Say you've a machine 3ft long, 200oz-in motors etc and possible to make 200ipm, moving from one end to the other the machine would accelerate for half the distance and decellerate the other half and depending on the Tcnc acceleration settings probably would not hit 200ipm anywhere! In return you're possibly loading up the machine to try and get those speeds. Put another way, If you double your theoretical ipm then the actual time it takes to get from one end to the other wouldn't be 50% half, more like 75% since you have to take into account the distances moved and the accelerations involved.

200ipm is possible if you've got the right match of load, motor power and tpi gearing. Its easier and cheaper to get less though.

If hobbycnc says he's got 150ipm on 5ypi and 127oz motors thats entirely reasonable. The drivers might match the motors better thou' and so he's getting full torque later in the speed range with the full 2.5a and 35v or so. Drop him a PM and ask.

you need to look at the torque curves for the motor.

Andrew

[ger21]

Originally Posted by fyffe555 If hobbycnc says he's got 150ipm on 5ypi and 127oz motors thats entirely reasonable.

Keep in mind that the HobbyCNC machine is a pretty small machine, with a pretty lightweight gantry.

[HobbyCNC]

Originally Posted by fyffe555 The motors are rated 2.9a unipolar? so thats about 2a bipolar series and 4a bipolar parallel? You shouldn't exceed the rated Amps for each wiring scheme. How are yours wired? The Xylotex is a bipolar driver so you have the choice of series at 2a and parallel at 2.5a. Series would produce the most power at full rating for the motor in bipolar series. get a torque curve and see what that might be. "to speed it up...." - the motors are staling at 30ipm? to increase this you either have to 'reduce the load' of the machine on the motors - that's friction, weight ( or inertia) of gantry and leadscrew, 'give the motors more power' - that's run the motors at thier maximum rated amps and high volts - you're limited by the combination of driver and motor specs, or 'lower tpi' - which is to say change the gearing of the machine. Less tpi, 10 instead of 16 say would mean the motor is turning slower for the same speed. Since steppers produce almost all thier power at low speeds you need to gear the machine to get the speed you want with the motor turning at the speeds its producing the power - just like a car. The TCNC 'problem' was me being dumb, *not* Tcnc. I'd set acceleration rates and speeds in TCNC by mistake. Nothing was going to keep up and too many steps per second meant the motor lost steps and stalled. It's a usefull exercise to calculate your target ipm speeds, convert that to steps and put that into Tcnc and then adjust up or down in small steps until the machine misses or you get the speeds you want. Together with changing the microstepping it helps see what sort of resonance and stall speeds your machine has. For example, I've one machine thats a pig at 1/2 steps and smooth and way faster at 1/4stepping, everything else being the same. 200ipm rapids is pretty fast! Is your machine up to it? and do you really need it? Say you've a machine 3ft long, 200oz-in motors etc and possible to make 200ipm, moving from one end to the other the machine would accelerate for half the distance and decellerate the other half and depending on the Tcnc acceleration settings probably would not hit 200ipm anywhere! In return you're possibly loading up the machine to try and get those speeds. Put another way, If you double your theoretical ipm then the actual time it takes to get from one end to the other wouldn't be 50% half, more like 75% since you have to take into account the distances moved and the accelerations involved. 200ipm is possible if you've got the right match of load, motor power and tpi gearing. Its easier and cheaper to get less though. If hobbycnc says he's got 150ipm on 5ypi and 127oz motors thats entirely reasonable. The drivers might match the motors better thou' and so he's getting full torque later in the speed range with the full 2.5a and 35v or so. Drop him a PM and ask. you need to look at the torque curves for the motor. Andrew

Actually, we've had to 300IPM..can't really run it that though. THATS why we say rapids at 150IPM. Cutting closer to 80-100IPM in light weight material.

Dave Rigotti

[Sanghera]

There we go. I got them. I'm not sure what kpps means, but I'm sure I'll find out.
Oriental motor has great support. The file is over the attatchment limit.
Thanks.

[WP1]

kpps would likely refer to "Thousand (k) Pulses per Second". This would refer to the step pusle rate that the CNC control software needs to generate to move the axis at a given rate inches or millimeters per minute.

For rate of say 60 inches per minute with a 20 threads per inch leadscrew axis driven by a 1.8 degree per step stepper with a microstepping drive set a 4 microsteps your formula would go like this:

20TPI * 200 steps/rev * 4 microstepping = 16,000 step pulses per inch

60IPM is of course 1 inch per second so the CNC control software will need to generate 16,000 step pulses per second or 16kpps.

Pete C.

[Sanghera]

Is it possible to convert this to rpm?
Thanks.

[HobbyCNC]

Originally Posted by Sanghera Is it possible to convert this to rpm? Thanks.

150IPM with 5TPI leadscrews is 750RPM. Easily obtained with our 4AUPC driver board even at 35VDC.

Dave Rigotti

[Sanghera]

So, if I wanted lets say 175IPM with a 5TPI leadscrew at 8 microstepping the calculations would go as follows:
5TPI*200steps/rev*8 microstepping = 8000 step pulses per inch.
175IPM is about 2.92 inches per second so the cnc control software would have to generate 8000*2.92 = about 23360 step pulses per second or 23.360kpps approximately/
Is this correct?
Thanks