Controlling a BIG DC Motor
Bill Chennault
Posts: 1,198
All--
For quite some time, I have been interested in how to use a Stamp to control a·high current DC motor, like this one: Banebot. Notice that it will operate at 6vdc to 14.4vdc, has a stall torque of 18061 oz-in, and a stall current of 85 amps. Of course, in my original ignorance, I thought I would find a motor controller with those specs. Ha! Needless to say, I haven't.
Then I began to think that instead of controlling the duty cycle, I would control the voltage, which I think IS possible via a relay ladder, beginning with 6 volts and adding 1.5 volts per relay until I get to 12 volts. I know I would sacrifice torque, but this is a powerful motor and would doubtless serve my needs (on the low end) even at 6 volts and on the high end at something approaching 12 volts without ever getting close to the stall current limit.
I have been working on the circuit diagram for such a "relay ladder" using a Stamp and a TPIC6595 to drive the relay coils. The circuit still lacks capacitors and·the TPIC6595 interface. When I get them in place, I will post it for your criticism and help.
In the meantime, does anyone know a BETTER way to control such a large DC motor? (I talked to Banebot on the phone. They said they knew of no motor controller that would handle their high current devices. They also said they were working on just such a controller. When I asked them about a time frame, they became quite distant and said they really did not have a time frame but that it was an interesting idea. I ain't holding my breath.)
--Bill
ps One way to implement a PWM motor controller would be to find something that I GUESS would cover my practical operating range and then stick fuses in to protect everything when it turned out that I was wrong.
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You are what you write.
For quite some time, I have been interested in how to use a Stamp to control a·high current DC motor, like this one: Banebot. Notice that it will operate at 6vdc to 14.4vdc, has a stall torque of 18061 oz-in, and a stall current of 85 amps. Of course, in my original ignorance, I thought I would find a motor controller with those specs. Ha! Needless to say, I haven't.
Then I began to think that instead of controlling the duty cycle, I would control the voltage, which I think IS possible via a relay ladder, beginning with 6 volts and adding 1.5 volts per relay until I get to 12 volts. I know I would sacrifice torque, but this is a powerful motor and would doubtless serve my needs (on the low end) even at 6 volts and on the high end at something approaching 12 volts without ever getting close to the stall current limit.
I have been working on the circuit diagram for such a "relay ladder" using a Stamp and a TPIC6595 to drive the relay coils. The circuit still lacks capacitors and·the TPIC6595 interface. When I get them in place, I will post it for your criticism and help.
In the meantime, does anyone know a BETTER way to control such a large DC motor? (I talked to Banebot on the phone. They said they knew of no motor controller that would handle their high current devices. They also said they were working on just such a controller. When I asked them about a time frame, they became quite distant and said they really did not have a time frame but that it was an interesting idea. I ain't holding my breath.)
--Bill
ps One way to implement a PWM motor controller would be to find something that I GUESS would cover my practical operating range and then stick fuses in to protect everything when it turned out that I was wrong.
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You are what you write.
Comments
This probably won't be helpful since it's intended for use with a 24 volt DC motor. Usually larger DC motors operate at 24, 48, 96, 130 or higher voltages. This motor controller will handle 50 amps continuous and 100 amps peak:
http://members.tripod.com/~divelec/html/motor_controllers.html
I have had a great deal of success with the smaller motor controllers listed there. I've just never had an application for anything in excess of 35-40 amps.
Regards,
Bruce Bates
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Thank you for the link. I will definitely check it out. I do not imagine I have an application that will demand more current than 50 amps continuous!
--Bill
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You are what you write.
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- Stephen
I had actually thought of that. But, I plan to build an 8-leg walker. Therefore, I will have to get a lot of experience prior to paralleling motors. (If that is what you mean.)
--Bill
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You are what you write.
robotcombat.com/marketplace_vantec.html
You might also look here if you want to go REALLY big.· These are intended to control golf cart motors, but the interface appears to be fairly compatible with a stamp.· I'm working on an interface to one of these myself.
http://www.alltraxinc.com/Products_AXE.html
Greg
Gee. Their MC-7 operates from 12vdc to 36vdc. I did not find this out by reading those specs. I found it out because I e-mailed Elaine at www.DiverseElectronicServices.com·for some kind of hint or direction to find a controller that would operate a big current motor and SHE pointed me very politely at the MC-7. (I did not mention your name, but I did tell her that one of her very satisfied customers referred me to Diverse Electronics.)
Why wouldn't I just use the MC-7 to drive the Banebot motor? (Remember its nominal voltage is 12 volts.) Elaine also recommended that I might use a 35 amp fast-blow fuse to protect the controller just in case I did exceed 35 amps. However, the controller will tolerate 75 amps for 10 to 20 seconds.
Additionally, Diverse Electronics has schematics of a Stamp controlling the MC-7.
If you have time, tell me what you think.
--Bill
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You are what you write.
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- Stephen
Wouldn't that be funny?
In reality, in places their documentations says 12vdc to 24vdc, 12vdc or 24vdc, and 24vdc to 36vdc.
However, my new best friend, Elaine at Diverse Electronics, says the M-7 will work over 12vdc to 36vdc. I will probably find out.
Here is a (slightly modified so it will fit) schematic of a BS2 and the M-7 (note the "12 to 36 volt motor" text)·. . .
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You are what you write.
· First off I looked at your gear/motor and the DC motor does not look real big and I see that they post the stall current but the motor could probally only handle around 20- 30 normally.
·· I have used the Victor controllers on big wheel motors chair that run at about 50amps at 24vdc·before and I have the 884 model but they sell a 885 controller www.ifirobotics.com/victor-885-speed-controller-robots.shtml
·With an operating voltage of 6v-30v at 120amps.
I believe this is true because the 884 I have ran fine off of a 12v battery make sure you order the propper voltage fan also.
One more thing you could run your motor at 24vdc and would probaly not do harm I have ran many 12vdc motors at 24vdc and they run a little hotter but are still running today, also just because you run 24vdc into the drive does not mean the motor will see 24vdc just run it at half speed setting and the drive will output 12vdc about and you can use the BS2 code to limit the voltage the 885 puts out and you could overdrive you motor if you wanted to.
Post Edited (bennettdan) : 5/17/2007 9:11:48 PM GMT
Great advice . . .·thank you for it!
I am learning as I am experimenting and building. One of the reasons I like the Banebot motors is because I have several of them. (I realize this is not a GOOD reason!) Another reason is that the larger, slower ratio motors have commercially installed and calibrated encoder options. This makes them very valueable to me.
What I am trying to say is the big'un I am looking at, plus its optional encoder, is worth the money to me just to LEARN a bit more. And, if I can make it do what I want, then I will probably use it and SOME CONTROLLER to build my big walker.
Thank you again for the advice. I never thought of doing it that way.
--Bill
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You are what you write.
About how big do you plan this walker to be? The motors look nicely made also it should o the job. Good luck
I would like to create something that looks like Edgar Rice Burroughs' Baanth. If you are an OLD science fiction fan, then you know that the Baanth lived on Mars along with other fascinating flora and fauna straight from Burroughs' mind. John Carter was the hero mystically teleported to Mars right after the Civil War. The John Carter·series of books by Burroughs is some of the greatest science fiction ever written.
The Baanth is basically a lion with 8 legs. A friend of mine is a vet and has offered to help me design an articulated spine--which is the key to natural movement, be it Baanth or kitty cat--which will accommodate 4 sets of hips. I have studied cat spines and although they are not too complex, when you try to put an extra set of hips into one, much less two extra sets, complications set in. For example, where there are hips, there are no ribs.
Anyway, how large will it be? Since I can't come close to the efficiency of Nature's design, I will have to compromise by reducing the number of vertebra in the spine from the·23 to 25 normally found in a common house cat down to about ten at the most. Each one will be larger than its Natural counterpart. Probably three times as large. This implies the size of the device: It will be about three times as large as if Nature had designed it. My speculation is that it will be about 4 or 5 feet long and stand 18" to 24" tall. (In Burroughs' immense imagination, my 'Baanth" will be·almost a·newborn!)
Of course, its name will be "Dejah."
I will dedicate a Stamp to each leg, which will (might be?) composed of one of those large Banebot motors and two smaller ones. The Stamps will communicate with a few PCs wirelessly. (I will simply put an access point in the Baanth.) The PCs will be the brains, including memory, of the device.
I have done a lot of big, crazy things. (Some have been successful.) This project will be by no means the biggest, or even the most expensive. But, it might well be the craziest. (Once, I did a big, crazy thing and wound up founding a company that now supports my big, crazy projects.)
--Bill
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You are what you write.