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Author Topic: 6 Wheeled Robot - Differential Steering  (Read 1648 times)
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Hi, all. So, I am using an 18 X 30 metal platform with six 10" wheels. I am only planning on making it 4WD with the front and back, not middle. I am using two 12V batteries for two 24V wheelchair motors, but I can't seem to find how I can get differential steering to work. I have seen some topics on H Bridges, but I was unsure whether I needed one for each motor, or only one for both. Thanks for the help!
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Since you only have two motors, I assume you'd have one motor driving both left wheels and the other motor driving both right wheels.

Since you're using differential steering you will need the left and right wheels to be driven independently so each motor will need a separate driver circuit i.e. a separate H-bridge, if that's the type of driver circuit you're using.
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Okay, thanks. And where would I connect a remote control sensor? Also, would I plug the batteries into the Arduino, and the motors into the H-Bridge? IE: How would it be set up? What connected to what? Thanks!
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Sounds like you should do more research on these topics, but in general:
- Batteries would be in series.
- Each The motor would be driven by an H-Bridge, and connected in the middle of the H.
- The H-Bridges would be connected to your 24V.
- You do not want to connect the Arduino directly to either battery.  It can't handle 24V, and it will be too noisy anyways for even directly to one battery.  You'll want some for of regulator (Either Switching (Lower power) or Linear (less noise, cheaper, easier, can waste lots of power)
- The Arduino would drive both the direction and the PWM (Speed) pins of each H-Bridge.  There is a more complicated version of the H-Bridge where you can get brakes, but to start at least, you just need the direction and PWM drive.
- Your Remote sensor depends entirely on what you are using to control it.  However, up high is usually good.
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Great! This is more information than I have found anywhere. Thanks a lot!
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One more question, actually. What would be the best way to make an H-Bridge, and how? I have a basic understanding of circuits, so I will probably just use a bread board. Not sure how to make the H-Bridge, though. Thanks again!
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Not sure how to make the H-Bridge, though.

Buy it.  H-bridge controllers are widely available and reasonably priced.
Make sure you leave headroom on the voltage and current specs.
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Great! Thanks  a lot. I'll come back here if I have any more questions.
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Alright, so I will connect the H-Bridges to the Arduino, and the batteries and motors to the H-Bridge?
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Alright, so I will connect the H-Bridges to the Arduino, and the batteries and motors to the H-Bridge?

Yes. Your h-bridges - depending on what you buy - will likely offer different modes of operation; the better ones will offer R/C mode (use the Servo library to command them - easy-peesy), TTL serial mode (some also offer full RS-232, USB, and sometimes ethernet), or PWM mode (which will be a couple of pins you supply PWM signals to - one to drive the h-bridge "forward", the other "reverse").

If you are building all of this - or have built it - I trust that you do understand that your h-bridge controller will need to be very powerful, and thus will likely be very expensive...

Also - you may want to rethink just driving two wheels on a side - you'll likely have much better luck running all three wheels at once on a side...
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Great! This is more information than I have found anywhere. Thanks a lot!

~million hits, very common robot platform.

https://www.google.com/search?as_q=DIY+skid+steer+robot+&as_epq=&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=&as_occt=any&safe=images&tbs=&as_filetype=&as_rights=
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Try this H-bridge: the L298, made by ST. It's dead simple to use and not very expensive (~$5 or so).

http://zapterra.com/systems/articles/electronics/l298-motor-driver-tutorial-arduino/
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Also - you may want to rethink just driving two wheels on a side - you'll likely have much better luck running all three wheels at once on a side...

Planning on putting gears on front and back to make it 4WD. Would that work?
And would that L298 motor driver work for my purposes? To clarify: I am only using two 12V batteries total, even though the motors are 24V. Not sure on amps, but probably peaking at 35ish.
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oops, no way then, the L298 is only good for 4A...
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Not sure how to make the H-Bridge, though.

Buy it.  H-bridge controllers are widely available and reasonably priced.
Make sure you leave headroom on the voltage and current specs.


I'd have a look at the Polulu high current H-bridges, probably upto handling a wheelchair
motor at half voltage.  Something like this: http://www.pololu.com/catalog/product/2502
seems appropriate.  Note that forced-air cooling of the motor driver board is assumed for those
current levels.  The chips used are actually multiple discrete MOSFETs and a controller chip mounted in
a single package, about the neatest solution for a power H-bridge there is.
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