How do Stepper Motor Drivers Overcome the Speed Restrictions Due to a Charging Coil?

[Voicecoil]

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(**Notes on Supply Voltages in the table: I used 68V for the NEMA 23 because that's what I'm using even though it's 20% above maximum recommended. The 77.78V NEMA 34 values are RMS values of the specified 110Vac shown in their datasheets. I figured this would be a reasonable DC value to use. I chose 48V for the 3.4Nm because 77.78V seemed way too high.)

Are you sure the 110V AC figure isn't a RMS value to start with? It's the normal was to quote an AC voltage unless you specifically say "110V AC pk" - anyway it does say also 5.9A constant current, so the voltage is kind of irrelevant.

[mattnedgus]

Are you sure the 110V AC figure isn't a RMS value to start with? It's the normal was to quote an AC voltgae unless you specifically say "110V AC pk" - anyway it does say also 5.9A constant current, so the voltage is kind of irrelevant.

To be honest I wasn't entirely sure, but it felt right.

For the three NEMA 34 motors respectively I used the maximum voltages (32*sqrt(L)) of 42, 64 and 82Vdc. The specs from the same manufacturer declared Vdc for the NEMA 23 and Vac for the NEMA 34 speed-torque graphs. My logic was that the drivers for these motors can be attached directly to a 110Vac supply like in the US and thus would have a numerically lower DC equivalent.

If I use 110 as the value for the supply voltage in the equations I also get 1645, 750 and 552RPM respectively for the max speeds for these same motors. It takes the power for each upto 649, 605 and 506W respectively. These values just felt way too high.

The supply voltage is one of the factors that determines the time it takes to reach the 5.9A maximum current. A higher voltage fills the coil to 5.9A faster. For example on my motors I get a current rise-time of 0.198ms and a max 759RPM on a 68V supply but if I were to swap this to a 36V supply the rise time goes up to 0.373ms and I get a max theoretical RPM of 402.

I'd really like to know what effect chopping stepper drivers have on the maximum speed of a motor and how half/microstepping the motor might influence these values though!

[Robin Hewitt]

History is against you. The problem is that some bod in America decided that all stepper motors should be 2 phase, 200 full steps/rev regardless of the frame diameter, and that holding torque was actually something worth printing on the spec. sheet. The Chinese shrugged collectively and said, "Whatever" and set about making them.

Unfortunately as motors get bigger the inverse square law is not on their side so they lose power. Holding torque can be enormous but it is the pull in torque that moves you to the next next step. Pointing this out to people who have already spent money on enormous motors and unsuitable toroidal transformers, is not going to win you any friends on places like this.

You may think you can overcome this by putting in loads of microsteps but then things become springy and your tolerances quickly become slack.

You obviously appreciate the problem or you would not have asked. If you have not already blown your budget, go to the Oriental Motor Company web page and look up some speed/torque graphs for their 5 phase motors.

[mattnedgus]

History is against you. The problem is that some bod in America decided that all stepper motors should be 2 phase, 200 full steps/rev regardless of the frame diameter, and that holding torque was actually something worth printing on the spec. sheet. The Chinese shrugged collectively and said, "Whatever" and set about making them.

Unfortunately as motors get bigger the inverse square law is not on their side so they lose power. Holding torque can be enormous but it is the pull in torque that moves you to the next next step. Pointing this out to people who have already spent money on enormous motors and unsuitable toroidal transformers, is not going to win you any friends on places like this.

You may think you can overcome this by putting in loads of microsteps but then things become springy and your tolerances quickly become slack.

You obviously appreciate the problem or you would not have asked. If you have not already blown your budget, go to the Oriental Motor Company web page and look up some speed/torque graphs for their 5 phase motors.

Thanks Robin, I'll take a look them - my options are still open.

Ah, it wasn't my intention to offend anyone - I couldn't find the information in a way that I could understand and hoped that maybe by sharing what I'd found it might help someone else later down the line.

To be honest I think I fell lucky on my current machine. It was my 2nd build (after trying V rollers on L alu-extrusion with ACME and T6-something drivers - it was hopeless!) and I had some excellent advice from Gary at Zapp regarding the motor and driver combination. I'd just hoped to increase my performance on this new build and didn't want to risk the outlay before I had a slightly better understanding, especially when I've read more than once about NEMA34's not necesarily providing the hoped increase.

[Robin Hewitt]

Ah, it wasn't my intention to offend anyone

I am sure you will not offend anyone. Sadly I am an incorrigible know it all and my foot is permanently in it

[m_c]

You are correct in that nema34 motors usually don't give you the required performance increase above nema24 motors.

In all honesty, given the speed you're looking for, I'd look at servos.

[mattnedgus]

You are correct in that nema34 motors usually don't give you the required performance increase above nema24 motors.

In all honesty, given the speed you're looking for, I'd look at servos.

I'd love to but aren't they about £500 (motor+driver) per axis?