Chris Savage and All: HB-50?

Bill Chennault

Chris and All--

The HB-25 is the greatest thing since sliced bread!

However, robots are getting larger and larger. Even Parallax has some larger ones coming down the road. The WORLD needs more capable motor controllers, particularly motor controllers able to handle more current.

Is an HB-50 feasible? HB-75? Dare I mention an HB-100? (I've got some 82 amp stall current motors I would love to use!)

I know nothing about these things, but it feels like an HB-50 should be doable. (How's that for rational thinking?)

--Bill

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You are what you write.

Chris Savage

Bill,

The HB-25 is based on an H-Bridge IC which can handle 25 amps. To meet this current capability certain thermal considerations must be realized and on the HB-25 this is where the heat sink and fan come in. I’m sure you can imagine the tight tolerances involved in mating the heat sink to the bottom of the IC as was designed, especially when the IC is a surface mount package. The HB-25 is quite a marvel in the way this was all handled, resulting in thermal specs exceeding the requirements of the H-Bridge IC.

There is also a small microcontroller which takes the servo pulses and converts these into the PWM signal fed into the H-Bridge. The useable voltage range is a factor of many things; but having the microcontroller and fan stay within limits and not require a regulator means that their voltage requirements defines the usable voltage range.

Now H-Bridges aren’t rocket science. It wouldn’t be too hard to find some decent complimentary MOSFETs to create a nice H-Bridge capable of handling 50 amps or more. But you also have to keep the MOSFETs cool and doing that in a small space isn’t going to be easy. On top of that parts which can handle higher current will most likely be through hold parts, further increasing the size. Next you have the considerations of the controller for the PWM. What voltage range do you support? 24V motors are also common, but if you do that you need a regulator for the controller. Regulating 24V down to 5V is going to dissipate some heat. You also have to be sure that current spikes on the H-Bridge don’t deprive the controller of power.

Time these days is at a premium, but I will, at some point, give this concept some further though and see what could be done. In the meantime I would poke around and see what out there can handle high current, at what voltage and the cost. That would help define whether or not it would be cost effective to build one from scratch. Take care.

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Chris Savage
Parallax Tech Support

Bill Chennault

Chris--

Thank you for such a complete explanation . . . in terms I can understand!

--Bill

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You are what you write.

RobotWorkshop

Hello Bill,

If you find that you've exceeded the capacity of the HB-25 there are actually quite a few options out there for you. I contribute the explosive growth of motor controllers over the last 5+ years on Battlebots and other combat robots. During some of the early events a lot of the people competing were frustrated by the inital lack of high current controllers so quite a few started designing their own. There was even an Open Source Motor Control project which worked out surprisingly well. I used a pair of those OSMC controllers with excellent results on a 120lb robot.

Most of the controllers accept the normal R/C type signals that most people that work with the Stamps are familiar with. Some of the controllers will handle mixing for tank style steering and some others now have more advanced features.

Some sources for high current controllers:

http://www.vantec.com/

http://www.robotpower.com/

http://robot-solutions.com/RS2/

http://tech.groups.yahoo.com/group/osmc/

These are just a few options and with a little searching you'll turn up a lot more.

Robert

Bill Chennault

Robert--

Thanks for the links!

Currently, I am using HB-25s to control 42 amp motors. Of course, the motors never draw anything even close to 42 amps, but it would be nice to have a controller that would handle it if such were the case. (I doubt they are drawing over five to·seven amps even under "heavy" use. I do not know how to measure it, though.)

--Bill

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You are what you write.

Brian Carpenter

try www.castlecreations.com they have speed controllers also

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