Motor Mount/Wheel Kit Position Control Commands without HB-25

Chuck Rice · 2009-02-20 20:55

I am using the MMWK with a third-party h-bridge. Do some of the commands only work in conjunction with the HB-25 h-Bridge? If so, which? The Datasheet does not seem to indicate.

QPOS         =      $08            'Query Position
  QSPD         =      $10            'Query Speed
  CHFA         =      $18            'Check for Arrival
  TRVL         =      $20            'Travel Number of Positions
  CLRP         =      $28            'Clear Position
  SREV         =      $30            'Set Orientation as Reversed
  STXD         =      $38            'Set TX Delay
  SMAX         =      $40            'Set Speed Maximum
  SSRR         =      $48            'Set Speed Ramp Rate

Tom C · 2009-02-20 22:20

Chuck,

If your third party h-bridge does not accept standard RC PPM, like the HB-25, then you might have a problem getting the MMWK controller to work with it.

Regards,
TCIII

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If you are going to send·a Robot·to save the world, you·better make sure it likes it the way it is!

Kevin McCullough · 2009-02-20 22:20

Hi Chuck,

The Position Controllers have the ability to generate the pulses necessary to control HB-25 motor drivers. These are basically standard servo-type pulses where 1.5ms is stopped, 1.0ms is full one direction, and 2.0ms is full the other direction. This was provided as a convenience to customers, but it is not required that HB-25s be used with this kit.

Additionally, the Position Controllers do not have to be used to control motor drivers at all. They can essentially be thought of as position SENSORS that record and store the current position and speed of the wheel. But they also have the added functionality of being able to control HB-25s for automatic simple motion control. If you don't want that added functionality, no sweat, they still work really well as a position and speed sensor (since that is half of what they were fundamentally designed to do).

Now to get more into the specific answer to your question... if you are not using an HB-25 (or similarly controlled 3rd party motor driver), then any commands that are specifically used to control the HB-25 are not applicable. It will not hurt anything to send these commands, but it's just that they affect an output that will not be connected to anything. These commands would be:
CHFA - Check for Arrival
TRVL - Travel Number of Positions
SMAX - Set Speed Maximum
SSRR - Set Speed Ramp Rate

The above commands only really apply when the Position Controller is being used to control the HB-25 motor driver. For example, it doesn't do any good to set the speed ramp rate, when the device is not being used to control speed ramping. The rest of the commands work just the same as normal, and are described in more detail in the product documentation. It is perfectly acceptable to use your own microcontroller, and/or motor driver with the Motor Mount and Wheel Kit. It is very much designed to be cross-platform compatible. Out of curiosity, what microcontroller and/or motor driver are you planning to use?

Hopefully this clears up any confusion there might be. Have fun!

-Kevin McCullough

Post Edited (Kevin McCullough (Parallax)) : 2/20/2009 10:30:19 PM GMT

Chuck Rice · 2009-02-21 02:05

That pretty much matches my understanding, and what I expected, but though the position encoder works well, I do not seem to be getting back valid speed data.

I use a Propeller to read the encoders and drive the H-Bridges.
The (Simple-H) H-Bridges I am using are driven by L298-type signals.

I just wanted to make sure that I should expect information back from the speed query, before I did to much hair pulling.

Thanks for the info. You should update the manual! [noparse]:)[/noparse]

Motor Mount/Wheel Kit Position Control Commands without HB-25

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