Using HB-25 for tank steering
Grievousfish
Posts: 54
I want to hack·three, two-wheeled FlyWheels RC toys that I bought really cheap into a six-wheeled, tank steered platform for a robot I am working on.· Each of the FlyWheels has two DC motors (w/ metal gears!).·
Does anyone know if·HB-25 will accept three motors wired together on each of·its' two motor channels or·will I need to daisy chain multiple HBs?
Thanks in advance for any assistance!
Post Edited (Grievousfish) : 6/4/2007 6:17:35 AM GMT
Does anyone know if·HB-25 will accept three motors wired together on each of·its' two motor channels or·will I need to daisy chain multiple HBs?
Thanks in advance for any assistance!
Post Edited (Grievousfish) : 6/4/2007 6:17:35 AM GMT
Comments
I've never used an HB-25 so I can't help you there, but here are a couple of comments.
I'm not sure if it was a slip of the fingers or not, but you don't want to wire these motors "serially", they should be wired in parallel.
Second, presuming these are fully reversible motors, you might want to consider this. Have the three port-side (left side) motors wired M+, M- and those on the starboard-side (right side) wired M-, M+. This will permit you to use a FORWARD command on both sides to have the port-side operate in a clockwise direction, and the starboard side operate in a counterclockwise direction, thus moving the platform forward. The same would be true of using the REVERSE command.
If you don't do that, then you will need to issue a FORWARD command to the port-side motors, and a REVERSE command to the starboard-side motors to cause forward motion.
This COULD be done either at the hardware or software level, but if you do it at the hardware level, it's far more transparent, and far less confusing IMHO.
Regards,
Bruce Bates
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Yes, the motors are fully reversible.
Thanks for the wiring suggestion. I am afraid I am going to have some major spaghetti trying to tie starboard motors and the port motors together. I am trying to use the original toy housings which has the motors laying right next to each other but oriented in opposite directions. I figured that was the easiest way of keeping the gearing all together. I am trying for an articulated mounting so that the robot will have some additional flexibility.
The starboard and port motors DO NOT need to be tied together. All starboard motors need to be tied together if they are to operate in unison, and all port motors are to be wired together if they are to operate in unison. The only thing that needs to be changed is the feed wiring (the power wires to the 3 + and 3 - wires) on ONE SIDE. That will implement my suggestion above.
In no case does the mounting need to be changed, unless you choose to do so for some other reason.
Regards,
Bruce Bates
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·· Each HB-25 has only one channel.· The M+ and M- lines both go to the motor.· You statement above made me think you were thinking something different.· I remember a customer who had M+ to one motor, M- to another, and then the other leads from each motor going to ground.· That is not how these work.· But you can Parallel the motors.· I have recently done this myself on a platform which uses dual-motors per side.· As stated above the motors need to be wired the same on each side, although one side should have the motor leads opposite the other side.· If not you will just need to change the PULSOUT values for each side.· Take care.
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Chris Savage
Parallax Tech Support
I gather from the replies that as long as I wire everything correctly, I can control the HB's dual channels separately and achieve tank steering.
All of what you said above is correct. Just to complete the entire thought, there is one more consideration, but I don't sense it will be a problem in your case.
One needs to add up the total amperage used by all of the motors which will be on a given HB-25 and ensure that it doesn't exceed the amperage capacity of the motor controller. This limit is not unique to the HB-25, it is a standard consideration when using any motor controller, whether with single or multiple motors.
Regards,
Bruce Bates
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The stalled rotor amperage is generally used as the maximum current that any given motor will draw, and it doesn't generally vary. If you don't determine this maximum current before it occurs, there is a good chance that you might exceed the capacity of the HB-25 and ruin it, should it occur. You could take the maximum amperage that the HB-25 can produce, divide that by 3 and fuse each motor appropriately. That way the fuse will blow rather than the motor controller!
That above is far from a perfect solution, but it's fairly straightforward.
Regards,
Bruce Bates
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I am pretty sure that HB-25's have a built in fuse,(the green thiing with 30 on it) but you might want to check the data sheet(http://www.parallax.com/dl/docs/prod/motors/HB-25MotorController-V1.2.pdf)
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D Faust