Introduction
I am working on a Mechanical Engineering senior design project building a 40lb tank robot driven by a wireless PS2 controller. Following is a basic schematic of the control plan:
The microcontroller is an Arduino Uno. For Arduino, the base frequency for pins 3, 9, 10, and 11 is 490.196078 Hz. The base frequency for pins 5 and 6 is 976.5625 Hz.
The motor contollers are Cytron 10A, 3-25V Single DC Motor Controller (http://www.robotshop.com/ca/cytron-single-dc-motor-controller-2.html) Each Cytron motor controller is capable of "speed control PWM frequency up to 10KHz" and "supports both locked-antiphase and sign-magnitude PWM operation."
The motors are standard OEM windshield wiper motors (Monster Guts - Your Wiper Motor / Pneumatics Headquarters!).
The battery is an AGM motorcycle battery (12V, 18AH).
Questions
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What effect will there be (on signal transmission, power usage, noise, etc) of using low PWM frequencies such as 490Hz/976Hz?
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What will the effect be on motor performance? Is there tabulated data about the resistance and inductance of these common motors?
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Could anyone provide a sample of using locked-antiphase versus sign-magnitude PWM using Arduino?
Thank you for your help!
John
- What effect will there be (on signal transmission, power usage, noise, etc) of using low PWM frequencies such as 490Hz/976Hz?
I don't expect any for this type of (large-ish) motor, and in fact the lower frequency is better for lower power consumption of your motor driver. Low PWM frequencies are an issue for low-inductance (small-ish) motors but yours don't seem to be in that class.
- What will the effect be on motor performance? Is there tabulated data about the resistance and inductance of these common motors?
You'd have to ask the motor manufacturer 
- Could anyone provide a sample of using locked-antiphase versus sign-magnitude PWM using Arduino?
Sorry, no help here. It doesn't sound that tough though. For sign-magnitude PWM you set one pin high or low to indicate direction of rotation then use analogWrite() on the PWM pin to indicate speed. For locked-antiphase mode you use 0%-50% PWM for rotation in one direction and 50%-100% PWM for rotation in the other direction (50% PWM means no motion at all).
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The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons
I have plenty of outputs to spare so I think I will just use sign-magnitude PWM.
Could you provide a little more insight about how a 'large-ish motor' is rated? I believe due to battery power constraint it will not be running at its full power. Does large refer the inductance/resistance or the current draw? I would like to be able to operate at these speeds, it would save me the difficulty of modifying timer1 and timer2, but I want to make sure there will not be any issues.
Thanks
John
Large-ish does relate to current, which is usually closely related to resistance. The problem with low PWM frequencies is really inductance and higher-than-rated voltage. If you're using a 12V battery and you have a motor that is rated for 12V, it really doesn't matter unless your frequency is so low that you can actually see the motor speed up and slow down on every cycle. That won't happen at 500 Hz.
If (as is common with steppers) you're using a 12V motor with a 60V source (just example numbers) and PWM to deliver 12V average voltage, then a very low inductance could cause your PWM to essentially operate in a discontinuous mode rather than maintaining a constant average current in the coils. You'd want the time constant of the motor's coils (tau=L/R where L is inductance and R is resistance) to be at least as long as your PWM period.
I'd be really surprised if your motor (based on its picture) would have a tau=L/R small enough to be of concern. But....you could always try to measure these quantities and be sure.
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The DIN Rail Mount kit for Arduino: quickly attach your Arduino to standard DIN rail
RuggedCircuits:
Large-ish does relate to current, which is usually closely related to resistance. The problem with low PWM frequencies is really inductance and higher-than-rated voltage. If you're using a 12V battery and you have a motor that is rated for 12V, it really doesn't matter unless your frequency is so low that you can actually see the motor speed up and slow down on every cycle. That won't happen at 500 Hz.
The motors are rated for 12V and we have a 12V battery.
The motors are rated at 20A full load (stall current). However, two of them will be running simultaneously from an 18AH battery. Even if the battery is capable of outputting stall current to both motors (40A draw), the system will not be capable of this. The limiting component will likely be the motor controllers, rated at 10Amps each(with each motor run by a separate motor controller). Therefore, the motors will be 'seen' as 10A or less. Does a motor of this 'size' fit in the same category?
RuggedCircuits:
If (as is common with steppers) you're using a 12V motor with a 60V source (just example numbers) and PWM to deliver 12V average voltage, then a very low inductance could cause your PWM to essentially operate in a discontinuous mode rather than maintaining a constant average current in the coils. You'd want the time constant of the motor's coils (tau=L/R where L is inductance and R is resistance) to be at least as long as your PWM period.
I'd be really surprised if your motor (based on its picture) would have a tau=L/R small enough to be of concern. But....you could always try to measure these quantities and be sure.
The motors are brushed DC with a gearbox, as far as I can tell, and not steppers. I have attempted to look up LCR data for the motors but the data is scattered. I do not have LCR equipment so I will be relying on your intuition and some functionality testing.