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Robo master/slave project — Parallax Forums

Robo master/slave project

indyindy Posts: 13
edited 2014-04-02 09:24 in Robotics
Has anyone fabricated a master robot/slave confab? I am working on a moving target concept and have hacked a power wheels (type) ride on jeep for kids. It is capable of packing 60 pounds in semi-rough terrain so it has the beans to pack a 20 pound load. Currently the vehicle has remote control which works fine for a team shooting practice, but I hoping to guide the jeep with a robo brain. My first test will be with a robo vacuum that has a simple pattern governed by a front bumper that makes it go in to reverse and turn. I will use the signals from the robo vac to fire relays that will fire the jeep drive motors. On paper it looks very workable, but I am waiting on relays at the moment so when they arrive the real world test will be conducted.

If the robo vac works as planned my next step is to use a S2 to control the jeep. I am currently learning the GUI for the S2 and this approach will give the Jeep more options in movement. It appears I will have to suspend the S2 on a frame so the wheels can turn and send signals to the jeep drive relays. It looks like the biggest challenge will be to find 9 volt relays for the S2 to Jeep relays.

One might ask why use a master/slave configuration? My thoughts were to save time and money whereas the Jeep was right at $200 and saved the cost and time of fabrication of a frame, purchasing motors,etc. I am not experienced in programming so using the S2 brain will save me lots of time, and the motion patterns I need will be basic. The shooting range will relatively free of objects so a timed travel in one direction or another should suffice.

I do have a remote kill switch if things spin out of control and the shooters are attacked by the target.

So any thoughts, comments experiences will be appreciated.

Comments

  • ercoerco Posts: 20,256
    edited 2014-03-31 10:13
    Neat project.

    How are your turning the steering wheel? Those Power Wheels typically use two seperate motors on each of the rear driving wheels in lieu of a differential.

    Relays are simple enough to use, even with a modest BS2. You can program such a bot to run specific patterns if you want to add wheel encoders: https://www.youtube.com/watch?v=PX0IhUqnwrk
  • indyindy Posts: 13
    edited 2014-03-31 17:28
    Very cool video. I am hoping the S2's brain will do the similar as the video shows.
  • indyindy Posts: 13
    edited 2014-04-01 07:09
    Is it practical to use a 9 volt relay to control a 12 volt power relay? i.e 9 volt signals from robo motor to a 9 volt relay that controls a 12 volt relay for the slave motor drive. I am not finding a 9 volt relay rated for the amps I need for the slave drive motors that run about 20 amps.
  • ercoerco Posts: 20,256
    edited 2014-04-01 10:36
    Uh oh. 9 volts, as in the S2's six AA batteries? My Spider sense in tingling.

    Are you planning to take the wires off the S2 motor and hook them to a relay? That won't work.
  • indyindy Posts: 13
    edited 2014-04-01 15:47
    Yes I was planning on using the signals to the S2 motors to fire the relays. I understand the front wheel has to keep turning so I was considering using one of the motors to drive the front wheel via a friction drive. Please advise why the signal from the motors will not work. My tests with the robo vac indicate it will, but the voltage from them is 13.59 which makes it easier to fire a relay. Heftier battery too. No encoder just a timed device to fire the front bumper to make a change in direction. I will also install a bumper switch on the jeep so if it runs into something it will reverse direction. Anyway I was hoping the eventual hookup with the S2 would allow me to program some patterns such as a figure 8, square etc. Your thoughts are welcome.
  • ercoerco Posts: 20,256
    edited 2014-04-01 16:05
    The S2 motor outputs are either PWM or PCM (rapid pulsing signals) through a polarity-reversing H-bridge, suitable for motor speed control, but not bang bang relay control. Apples & oranges.

    Likewise apples & oranges on the two chassis designs. Your power wheel uses more complicated Ackerman steering, completely different from the simple differential steering on the S2 and Roomba. No easy way to mix the two.

    Suggest you start small and work up to a power wheels size bot.
  • indyindy Posts: 13
    edited 2014-04-01 16:57
    Well that settles it, did not know the S2 was not a solid standard voltage output. Using the robo vac however the signal to the motors appears not to be PWM, so once the relays arrive it will be go or no go with that approach. Thanks a bunch for your input, it has saved me some serious head scratching and loads of time to discover it would not work with the S2. I think I have a simple solution for the steering issue and if so I will send you a video once it works or not.
  • indyindy Posts: 13
    edited 2014-04-02 06:23
    Ps
    What program and micro did you use in robo that remembered the path?
  • ercoerco Posts: 20,256
    edited 2014-04-02 09:24
    BS2, I wrote the program.
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