The 10% would be added to every speed test though. So it might be a scale on the whole thing. But you can’t avoid accelerations IRL either.
I don’t think it needs to be ultra precise. Just need ballpark numbers. Since every build will be different, actual numbers don’t matter as much as the broad result. Just want to know if higher voltage allows for 2% more speed or 20%, or any significant extra power in the range we typically use. As much as I want to actually classify the steppers I have, I rather understand this power supply debate more.
The other part is if people really want to have speed 20T pulley will shift the power curve / RPM over 20%.
So I did a little testing with 12V and 24V.
In a nutchell, nothing in the typical use case for a V1 CNC machine shows any difference between 12V and 24V. The one thing that I do where there might be a difference is that my Z rapids are faster than 12V can do at full torque.
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Rough estimate, how much faster? 30mm/s to 35mm/s?
I keep wanting to run those tests but I keep sneaking away to get some jetski time in. It is very therapeutic for me.
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My Z rapids go up to 50mm/s. Never even tested that at 12V lifting the gantry.
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Okay I finally started farting around with this.
Mind blown 
for sure.
My build, fully loaded router and vac hose just as I use it. 12V
Zmax speed, 63.8mm/s
Xmax, 300mm/s
Y max, 285mm/s
See those numbers, that is nuts, fully loaded CNC. To be very clear, everyone’s CNC will not match these numbers. My firmware normally limits the XY to 50mm/s, Z to 15. Clearly I can raise that a bit.
24v…here is the catch Acceleration. RepRap Calculator - Original Prusa 3D Printers
Z max (stock 80mm/s/s) 75mm/s *accel limited. Plenty of room for more. Too much experimenting so I played with the X instead.
Xmax (stock 180mm/s/s) 330mm/s *accel limited. Okay hold your britches ----800mm/s/s 650mm/s and this number did not fail it just gets maxed out for the axis length I have.
let me repeat that one, 800mm/s/s 650mm/s
So lets discuss this a little bit. Clearly the 24v PS allows for faster rapids. Now in terms of actual real world use, rapids will help overall but 90% of the time is spent cutting, These numbers have no effect on this.
So to even take use of this we can not really speed up cutting accel, we could speed up travel accel though. I just don’t think it makes too much real world difference.
I also did check holding torque with a luggage scale, it is the same. Holding torque is current dependent, and current equals heat. This can’t be turned up until we move to metal stepper mounts. X axis was holding at more than 5kg (tmc 80% holding current), Z axis was more than 30kg holding!
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Thats nuts.
My mental model says that the max force drops with speed (even though the current stays the same). Your speed test is finding the place where the force needed to accelerate the machine, plus the force needed to overcome friction is equal to the max force available that speed. Higher speed and the force drops below the force needed to move it.
Adding loads to it would add more to the needed force, which would bring down that top speed. My guess is that it would mean the difference between those max speeds would be even more different.
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That was more or less my findings. I have mine set more conservatively than you do, but I just bumped up the rapids speed until I was satisfied.
I do have some projects that have a lot of small cuts in stuff, with larger spaces between, so the rapids does have some real world impact there.
I did not find any difference in the speeds that I am able to cut with 24V vs 12V. Most of my cutting is in birch plywood, some solid hardwoods like cherry, walnut and oak, and the unavoidable MDF cutting, of course. Of these, MDF is probably the slowest.
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Unless you use multiflute end mills, any speed benefits from 24v are pretty much wasted while cutting. On 24v I did 100mm/s feed and 800mm/s/s accel for the cnc race with a 3 fl end mill and managed a hair over 80mm/s feed in aluminum feeling out the limits of my machine.
My feeling is that 12v is more than sufficient to get the job done. Only really need 24v+ if you really want to push the performance envelope to the absolute limit.
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I agree cutting speeds are not any better but what about Z rapids?
For X/Y rapids I wouldn’t think the higher top speed would help much since you won’t generally have enough long, fast travels, but maybe you could more easily hit the Z speed limit. If your job has lots of short segments and you are conservative on the clearance plane, the Z speed for rapids could matter, perhaps?
I’m thinking about the scenario where you’re making a cribbage board or maybe ascii art with a pen.
Maybe not a huge difference but still worth it.
Or if you are dead set on using a one-start Z screw and you use 24V, maybe you cut the Z speed in half instead of 1/4, and that could matter.
You are probably right about no need for 24V for common routing tasks, but there are a variety of applications where 24V, perhaps combined with a 32-bit board, might provide some benefit to address things like these.
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Some LowRiders use 1-start lead screws to avoid the Z drop when the machine is unpowered. This requires a 4X lower max feedrate.
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Before Covid, I was cutting foam cosplay props for my daughter. I was pushing max feedrates and would have gone higher if I could have.
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On the Primo/Burly, the max Z axis feedrate is below the cutting feedrate for X and Y.
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I have some pen projects planned that may benefit from higher feedrates.
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Laser engraving might benefit from higher feedrates. Some of the better laser engravers report a max feedrate of 12,000 mm/min.
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I think the 15mm/s we run now is a too conservative. Mine doesn’tr cut out until after 60mm/s. I think if you found your machine’s max and dropped it 15-25mm/s you would be safe.
That could make the biggest difference. I have asked my supplier about some more 24v PS but the ones they currently have are red=negative and white=positive. That is going to cause too many issues.
Faster than the numbers I am getting with my 12V? The firmware is only limited so newcomers have a safety net on poor gcode. We can obvioulsy run much higher that we curerntly do.
Not have a hose and router on there I don’t see why you could not run much, much faster. This test showed good builds can fly around. 24v allows for more but if you see it move more than 100mm/s you might think twice about wanting more. At those speeds a mistake can break things.
200mm/s,
Already able to run faster than that.
We definitely have seen people skipping steps with the default firmware, 12V and 1 start leadscrews. It is hard to tell if that is a fluke, or common among people using 1starts. But dropping the max speed, or going to 24V has solved all of them, I think.
It would be easier if I could actually get my hands on a build that is skipping steps so I could know for sure why.
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Maybe we need a calibration routine gcode that proves out a build. Seeing that 80+ is possible, 10-15mm/s should be easy.
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12V with 1 start leadscrews will slow jobs with a lot of up/down, to the point I feel it’s worth the upgrade (PCB drilling for example). My rapids slowed down well over 50% with 1 start, but I never actually tested the max speed with 4 start (was just 35mm/sec). It might also be fun for doing big rapids on a full size LR3.
I think testing should consider step rate. Velocity is the product of mechanical reduction. So it doesn’t account for changes in drive ratio due to leadscrew pitch, pulley tooth count, or whatever. mm/sec does matter wrt the kinematics of the gantry though, and is a relevant measure of cnc machine performance. But for sure, if you include step rate in the dataset, there will be a more clear conclusion as far as what different drive supply volts can do.
My general understanding is the higher voltage allows higher switching frequency (thus more RPM), due to the lower rise time across the inductive coils in a motor. So I don’t think 24V would cause more motor heat until it surpasses speeds that 12V could do. I’m not sure what happens with the driver. It would seem there would have to be more losses with more voltage to drop at lower RPM, but I’ve seen many posts that modern chopper circuits handle that efficiently where the extra heat is not an issue.
[edit: …numbers for a starting point. My 1 start primo is configured for 1600 steps/mm, and 12 max mm/s. That’s pushing it on 12V; 15mm/s and it’s definitely skipping a lot of steps. So around 19kHz, with tmc2209 at 1.4A.]
I would disagree. The driver controls switching frequency similar regardless.
The higher voltage allows the driver to fight back EMF. Any (fixed magnet) electric motor when spun becomes an electric generator. This is the intrinsic relationship between magnetism and electricity. The motor generates a magnetic field which moves the fixed magnets. Similarly moving the magnets past a coil of wire (Or the coil past the magnet, same thing) generates a current in the wire, even if the reason for the movement is a current in the wire. Since we’re moving the coil one way, the EMF generated in this manner opposes the incoming voltage.
The drivers do some interesting stuff with the effective voltage in order to keep the current limited. It switches the power on and off via PWM to keep the average voltage to the range where the current stays at the desired level. Because the load is an inductor, this really does act like an average, since the inductor serves to prevent changes in current that are too sudden.
Normally, current = voltage over resistance (I=V/R) so for a fixed value of I (eg: 900mA) and a fixed resistance, there is only a certain average voltage that you’ll ever use. Where it gets jiggy is that the motor is now acting as a generator, and trying to reverse the current flow. This ends up expressed as a voltage, too, but in the negative. In order to maintain the average current flow, the driver increases the duty cycle, thereby increasing the average voltage, to a maximum of the power supply voltage. (100% duty cycle.) The faster you spin the motor, the greater the motor’s power generated is, and the more reduction in available voltage you get.
Higher power supply voltage therefore increases the maximum RPM that you can spin the motor at, but as long as the power is still throttled by the driver, it does nothing to increase available torque.
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You can get that easily from the steps per mm, if you also consider the microsteps. The Z on Ryan’s machine is 400 microsteps/mm. The xy is 100. Both with 1/16th. So that is 25 steps per mm on Z and 6.25 steps/mm on xy. Just multiply Ryan’s numbers by those and you will get step rate.
what motors are you using? That’s an interesting fact!! 
