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Triboelectric Effect and ESD

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  • Triboelectric Effect and ESD

    Hi Tom!

    Thanks for the information on electrostatic discharge--we would like to add some suggestions for other teams, based on past experiences as well as research we have conducted this season.

    Last season, we suffered from ESD in practice and competitions. This resulted in us losing communication with the robot and losing matches as a result. Throughout the season we tried several prevention techniques--like anti-static spray and a Faraday cage--but neither solved our problems. While our robot worked most of the time during testing at home, we were regularly experiencing noticeable shocks from static when we touched the robot, and at the Eastern Super Regional competition we lost connection in our first three matches, which was really discouraging.

    This year we made a commitment to exploring ESD and the triboelectric effect, which is the charge developed when two materials come into frictional contact. (We first found it here https://www.trifield.com/content/tribo-electric-series/) Specifically, the triboelectric effect is the idea that different materials--further apart on the triboelectric series--can develop significantly larger charges from frictional contact than those closer on the series. Using an electrometer lent to us by one of our sponsors to conduct tests, we developed our own triboelectric series (below), focusing on materials and mechanisms used by FTC teams, which causes it to differ from the Trifield series. We have also attended other competitions to test other teams’ robots to understand the materials and designs that lead to ESD.

    In addition to the recommendations you had, we would suggest the following:

    Robot Design Advice:

    > Eliminate or reduce one material rubbing against another. E.g. Wheels rubbing on the mat, pickup mechanisms rubbing against the particles

    > If two materials must rub, choose materials with the desired properties, but that are close on the triboelectric series below

    >As you recommend, separate the wiring as much as possible from parts of the robot which build up a static electric charge

    >Put ferrite chokes on the wires where they enter electronic components


    The Triboelectric Series

    Materials: --- --- --- Examples:

    + Positive Ve +
    Polyurethane --- --- --- Poron foam
    Nylon --- --- --- Zip ties, omni wheel frame
    PLA --- --- --- 3D printing material
    Polycarbonate --- --- --- Lexan
    Duct Tape --- --- --- Duct Tape
    PETG --- --- --- Soda Bottle material, 3D printable
    Cap Ball --- --- --- Cap Ball
    EVA --- --- --- Foam Competition Mat
    Delrin --- --- --- Slippery plastic in bushings and bearings
    Latex --- --- --- Surgical tubing
    Neoprene --- --- --- Timing Belts
    HDPE --- --- --- Particles, Vortex elements
    BUNA --- --- --- O-rings, Andy Mark/omni wheel rubber
    Silicone --- --- --- Tubing, Cast silicone, AndyMark silicone wheels
    PVC --- --- --- Plumbing pipe
    - Negative Ve -

    We have posted information on the triboelectric effect on our website (www.gearticks.net > Useful Rescources > The Triboelectric Effect), which we will keep updated. We would like to hear other teams’ ESD experiences!

  • #2
    Thanks for taking the time to do the research and sharing your result and thought.
    A question: Would you suggest on how to reduce or eliminate "Wheels rubbing on the mat, pickup mechanisms rubbing against the particles"? These seem to be fundamental to the game. Even by carefully selecting materials, some materials are out of our control, for example, the foam tile of the field. So the only controllable material is what you use on your robot such as the wheel and with FTC's restriction on what wheels are legal and also the team's desire to have a certain properties (e.g. high traction), it's almost impossible to avoid static build up. Do you have examples on what FTC approved wheels are least likely to build up static on the field foam tiles?

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    • #3
      Originally posted by mikets View Post
      Thanks for taking the time to do the research and sharing your result and thought.
      A question: Would you suggest on how to reduce or eliminate "Wheels rubbing on the mat, pickup mechanisms rubbing against the particles"? These seem to be fundamental to the game. Even by carefully selecting materials, some materials are out of our control, for example, the foam tile of the field. So the only controllable material is what you use on your robot such as the wheel and with FTC's restriction on what wheels are legal and also the team's desire to have a certain properties (e.g. high traction), it's almost impossible to avoid static build up. Do you have examples on what FTC approved wheels are least likely to build up static on the field foam tiles?
      Hello! Thanks for your great questions!

      There are several ways to reduce excessive rubbing when driving and picking up particles. Some are fixing simple errors, for example on our robot from last year, two wheels connected by belt were slightly different sizes and one therefore rubbed on the mat, producing charge. This year, we also have to be careful not to stop suddenly with too much momentum, as it results in drifting which also produces charge.

      Within pickup systems one can also reduce rubbing. Often there is a simple solution, for example we’ve seen at recent competitions that people build pickup systems with zipties that are too long so they brush against the EVA foam mat when the pickup rotates. This is bad because they build up charge and zipties, being nylon, are therefore quite far from EVA and HDPE on the triboelectric series. Trimming the zipties eliminates rubbing the mat but leaves the pickup just as effective.

      As for the wheels, we have currently been experimenting, experiencing similar limits that you seem to have encountered. We have decided to 3D print the hubs of our omni wheels in PLA and PETG rather than use the original nylon because they are closer to EVA on our triboelectric series. We also are making our own drive wheels, 3D printing the hub and then casting tires onto them in a homemade 3D printed mold. We have experimented with polyurethane and two types of silicone for this casting--finding that the polyurethane causes our robot to have a very positive charge and the silicone a relatively negative. We then created wheels that alternated the two materials. Like your concern, we found that we didn’t like to drive with one of the silicones we cast because it didn’t provide as much traction. Ideally we would like to be able to cast EVA, latex or BUNA tires but we haven’t found a suitable source.

      By using different materials and different ratios between our two cast materials, we look to “perfect” our built up charge.

      Please respond with any more questions!

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