Calculating motor torque required March 26, 2014 11:53PM |
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Re: Calculating motor torque required March 27, 2014 05:40AM |
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F = m * a Force = mass * acceleration
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Re: Calculating motor torque required March 27, 2014 06:23AM |
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Re: Calculating motor torque required March 27, 2014 08:35AM |
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Re: Calculating motor torque required March 27, 2014 11:18AM |
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Re: Calculating motor torque required March 27, 2014 11:22AM |
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Re: Calculating motor torque required March 27, 2014 12:28PM |
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Re: Calculating motor torque required March 27, 2014 12:54PM |
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Re: Calculating motor torque required March 27, 2014 01:48PM |
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Re: Calculating motor torque required March 27, 2014 02:33PM |
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That 50uS assuming 20?kHz which the smoothie can output is not related to the coils, it perhaps related to the speed at which motor moves, because each step means 1 move, so ofc more moves per sec is more speed. But stepper driver does not care for that frequency, each step is processes one after another, means 1 move and nothing beyond that, the step frequency cannot be an input variable. Basically first assumption is wrong, and the approach is made from wrong direction. This part between uC and driver input, the step line, is just chip to chip communication, you can take it as a protocol, like I2C or SPI, or something like that, it serves just to send commands, but it does not directly influence what happens to the motor coils.Quote
MeltManBob
I[...] the capabilities of the micro controller to send pulses [...]
Re: Calculating motor torque required March 27, 2014 10:02PM |
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Re: Calculating motor torque required March 27, 2014 11:24PM |
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Re: Calculating motor torque required March 28, 2014 05:27AM |
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Quote
MeltManBob
So how do I find out what the maximum voltage is that can be produced by the driver?
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Re: Calculating motor torque required March 28, 2014 06:14AM |
Registered: 13 years ago Posts: 1,352 |
Quote
MeltManBob
It sounds like what you are saying about reaching the max current is the driver is capable of reaching voltages higher than the supply voltage in order to dictate the current limit which I've also read in the data sheet but I wasn't 100% certain about. This makes me think that the supply voltage dictates how high the driver can pump the voltage and/or how fast it can pump it because even if the driver can get a higher voltage to reach the current limit there has to be some limitation as to how high a voltage it can produce and consequently how fast it can get to the current limit.
So how do I find out what the maximum voltage is that can be produced by the driver?
No, the pulse signal on time has no significance whatsoever. On the step line nothing matters, not the frequency, not the duty cycle, not the pulse duration. You will see in datasheet something like step minimum pulse width, but that is just monitoring to make sure the step signal was valid and not an occasional spike. Other than that the pulse width is not processes further, if pulse width would mean anything else it would be dc servo not stepper. I have said all this like many times.Quote
MeltManBob
I'm assuming that the driver pays attention to how long the pulse signal on time is and then multiplies it by 2 to determine the time frame that it needs to turn on the current and then off based on the decay mode.
Re: Calculating motor torque required March 28, 2014 06:48AM |
Registered: 13 years ago Posts: 1,352 |
The sense resistor is put in series with the coil. There are 2 of them, one for each coil.Quote
MeltManBob
I looked at the datasheet some more trying to figure out how the supply voltage effects the output voltage even though they are not directly linked and couldn't find much. The trip current is set by Vref/(8*Rsense) and Rsense appears to be a combination of 2 external resistors. Basically what I'm not getting is that I've read that if you increase the supply voltage then you can drive the motors faster to the trip current but I'm not seeing where the correlation lies since the supply voltage is not the voltage used to calculate the current. Otherwise there wouldn't be any benefit of using a 24v supply over a 12v but I know that it is better to use a higher voltage.
Quote
MeltManBob
Anyway I'd like to reiterate that I would like to make sure the rest of my math logic outside of the drivers is good to go or not that way as we continue to hash out the details of the driver I can keep a big picture perspective. Ultimately I know that a faster time constant for a motor would appear to be best because the current/torque can build up faster BUT being able to actually calculate these things would let me figure out if a more powerful motor might be better even if it has a slower time constant but more than made up for it in torque. For example a smaller motor with a faster time constant that could reach it's rated current within some period of time 'X' compared to a larger motor where in that same time period 'X' it only reached 50% of it's rated current/torque but that torque being higher than the smaller motor. In that situation the more powerful motor would actually produce more torque. Thanks again!
Re: Calculating motor torque required March 28, 2014 07:14AM |
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Re: Calculating motor torque required March 28, 2014 07:55AM |
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Re: Calculating motor torque required March 28, 2014 08:54PM |
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Re: Calculating motor torque required April 03, 2014 09:01AM |
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Re: Calculating motor torque required April 03, 2014 09:02AM |
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