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Improved Whiskers on BOE Shield + A question — Parallax Forums

Improved Whiskers on BOE Shield + A question

tz3p9vtz3p9v Posts: 3
edited 2013-12-27 22:20 in Robotics
When I built my BOE-Bot with the Whiskers I discovered that the unit would have problems when just glancing off an object. The Whisker would move forward in some cases. So I revised the design somewhat and thought I should share -- if this has been shared before, apologies for the repeat.

I removed the center pin of the 3 header pin used as a contact for the Whiskers. I then moved the Whisker so it was between the remaining two posts in the header. This way the Whisker will contact the pin when Whisker move either forward or backward. Simple improvement that improves the sensitivity of the Whiskers. (see attached picture)

Also, I have a question - when I power up my BOT -- the Left server seems to get power for a short period -- the wheel rotates just a bit. The power switch is set to position 2. This happens with all programs upload and run. Thoughts? Is this normal and if not, what can do to stop it.

Thanks
Paul.
ChangeToWhiskers.jpg
640 x 480 - 103K

Comments

  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2013-12-26 16:21
    Analog servos can twitch a little when they first get power but no control signal pulses. Once the pulses start coming in the servo will then seek to its set point. If you set the switch to position 1, the servos won't get power, and should not (normally) move.

    As an experiment, try revising your programs to have an initial delay at the start. In this delay set the servos to stop -- i.e. 1500 microseconds -- for a second or two Within the period of this short delay, move the power switch to position 2. Do you still have any jerking of the servos?

    What this should do is start applying pulses to the servos before they are powered.
  • tz3p9vtz3p9v Posts: 3
    edited 2013-12-27 07:10
    Thank you Gordon,

    I will give it a try and report back later today.

    Paul.
  • Ken GraceyKen Gracey Posts: 7,387
    edited 2013-12-27 10:44
    Oh, and I think your whisker modification is great. That's what this kind of activity is all about - customize, modify, build, program and change improve it along the way. I've seen a lot of little whisker improvements but never this one. One that I really like is the single wire, big loop since it doesn't get caught on anything.

    Welcome to the forums, too!

    Ken Gracey
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2013-12-27 14:05
    Ken, didn't you have some whisker action going on for a while?
  • tz3p9vtz3p9v Posts: 3
    edited 2013-12-27 22:20
    To solve the "servo twitch" on reset, I added a second tone 2s after the first... at which point I then switch the power to position 2 from 1. This eliminates the issue nicely.

    As for the Whisker mod - glad to share...

    Thanks
    Paul.
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