Speed Controllers

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Speed Controllers

Postby thecleancompany » 30 Nov 2010, 02:45

I am trying to figure out the best speed controller to use to get a pair of 24 volt 8 amp DC motors to go slow, yes SLOW, and be able to move a load of about 2oo lbs for about 5 hours at a time before heading off for a recharge. Also what type of battery might be best.
Thanks,
Tony
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Re: Speed Controllers

Postby JoeC » 30 Nov 2010, 03:06

Have you looked at robotmarketplace.com, and Hobby King? There are a number of good controllers there.

Your request is a little light on information. Are the motors 8 amps maximum, or continuous? Do you know what the continuous current is? A lot of starting and stopping? Any hills or uneven ground? Are the motors always in sync, or are you hoping to vary the power to each for powerchair-like steering? If the motors were guaranteed to never draw more than eight amps, you could be conservative and add them to 16 amps, multiply by five hours, get 80 amp hours, and look for a battery in that size range. That's bigger than a typical powerchair battery- mind if I ask what this is for?
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Re: Speed Controllers

Postby thecleancompany » 03 Dec 2010, 20:48

Hey Joe
I am looking into a self propelled type of platform that can push a pair of commercial upright vacuum cleaners.
Motors suggested for use are 8.0Amp continuous current 24VDC which are available locally for me. The speed controller they suggest is a DL50 but not certain if I can turn down the speed slow enough to vacuum effectively. The parts and pieces add up quickly so I want to learn as much as possible.
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Re: Speed Controllers

Postby JoeC » 03 Dec 2010, 21:41

Do you plan to follow behind it and operate this machine with the joystick? The DL50 is a powerchair controller (not a very strong one), so it will let you move very slowly for vacuuming if you don't push the stick very far. If you're looking to remote control this, one of the robot controllers might give you a much easier interface and would provide plenty of power- and might be a lot cheaper!

The rating of "8 amps continuous" is meaningless, since you are not doing something continuous with this unless you're only vacuuming in a straight line on a flat surface without starting or stopping. That's not how I vacuum, and I think a more conventional method would include a lot of steering, taking off from zero speed, and pushing against a resistance. All of these things are likely to use more than 8 amps per motor, unless you have the gearing set for a very slow speed. If you gear this thing to only move at 2 to 3 mph (maybe even less) at full throttle, you'll have an easier load for the motors and batteries, and won't have to worry about turning down the speed controller so much.

It would be interesting to hear more about your application and where you're coming from.
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Re: Speed Controllers

Postby thecleancompany » 04 Dec 2010, 23:59

Hey Joe,
Thanks for some good suggestions. The stated gear ratio is 32.88:1 and I am not sure exactly what that means. And how will a 12" diameter tire effect keeping speeds down?
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Re: Speed Controllers

Postby JoeC » 05 Dec 2010, 08:21

The gear ratio of 32.88:1 means that the motor will spin 32.88 times for every single turn of the output shaft. This means that if you use a voltage that causes the motor to spin 3288 rotations per minute, the shaft will only spin 100 RPM.

The tire's circumference is how far the vehicle will travel with each revolution of the output shaft- so this 100 RPM output from a hypothetical voltage would cause the thing to travel at about 3.5 mph. You get that by multiplying 12 inches times Pi, then by 100 RPM to get about 3770 inches per minute- which you then can convert to miles per hour or whatever else you like.

That's just guessing that the motor spins around 3200 rpm 24 volts, which is a fairly normal number for most wheelchair motors that I've seen, but might not match what you're looking at. You'd need either more complete specifications or you'd have to measure it if you want to know for sure. Regardless, the RPM will be determined by voltage, and the speed will be determined by how many inches of tire pass along the ground with each rotation. You can always go slower by putting smaller wheels on the thing. If you're just using it indoors, you might get away with much smaller wheels than most powerchairs.
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Re: Speed Controllers

Postby thecleancompany » 05 Dec 2010, 18:10

Hey Joe,
I have found several 18-1 24 volt motors from NPC. These might be a better match for the platform to go slow as 18 revolutions of the wheels for every one spin of the shaft might be better. I keep reading on drives and controllers and when I better understand it I will post more intelligent questions.
TOny
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Re: Speed Controllers

Postby JoeC » 05 Dec 2010, 20:32

Hi Tony,

It's actually the other way around- the 18:1 would make the wheels turn FASTER than the 33:1- nearly twice as fast with the same motor. We also call the ratio the "reduction"- it's reducing the speed. A larger reduction will give the motor less speed and more torque.

I think a good way to go for you with this project might be to find an old powerchair (those often show up for very cheap or free on Craigslist), and use the motors and the controller together to get what you want. If it goes to fast, put smaller wheels on it. Use batteries that are the same as what it originally used.
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Re: Speed Controllers

Postby thecleancompany » 08 Dec 2010, 18:05

Thanks for all the good information. Hopefully will have this thing done in January.
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