Announcement

Collapse
No announcement yet.

USB Surge Protection

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    This time that we saw the arc the robot remembered the last command that was sent to it and kept driving. Basically the RC app froze and only remembered the last thing sent to it. However, throughout all of this we have been seeing the issue of randomly losing one or both controllers and having to hit start A or start B. In some cases we have had to unplug and plug the remote back in to get the start A to work. With the changes made today we haven't seen that issue either.

    Comment


    • #17
      Possible fix for static build up

      We're a Colorado team where the air is always dry. We had such a problem with static discharge early in the season that we couldn't test our autonomous codes because the robot would reset almost every time we went to pick up the robot. I was able to use Staticide spray on our mats and it worked very well, but not a global solution unless FTC starts insisting on it's use at competitions. I was able to obtain a electrostatic meter from work, and measured our mats at-6000 volts. The robot would get to +12,000 volts after an Autonomous run. When picking the robot up we'd often get a 1/4 spark. I had been involved with my son's science fair project a few years ago which involved levitating aluminized mylar foil above a charge plate. During that I learned about corona discharge from objects with high voltages on them. Corona discharge takes place at places on the object which are pointed. I thought maybe if I put many points on the robot I could dissipate some of the charge build up into the air. My first thought was "great, the safety inspection people are going to love a robot with sharp points all over it." I ended up using copper screening which I had left over from another of my sons Faraday cage experiments. I realized that cutting the screening would produce many sharp points along the cut line. The copper screening is good because it is highly conductive and the copper is soft enough that you can't puncture your skin with the points. We have an omni wheel robot. I taped the copper screening pieces next to each wheel on the aluminum guards we have next to the wheels. I used conductive adhesive copper tape for that. The voltages I saw after that where closer to +2,000 volts. We are currently using 4 "corona discharge devices" mounted next to each wheel under the robot. We point the copper screening down and space it about 1/4 to 1/2 inch above the mats. These are not grounding straps, so please don't tell me they are illegal. The voltages I've measured on the robot after I put these on are closer to 2,000 to 4000 volts. I don't feel I'm jeopardizing other robots because the robot is not at the same negative potential the mats are showing. I do think that by simply keeping some of your aluminum frame close to the mats you might be able to get a similar effect even without points. I haven't had time to prove this. I was hoping to perform real experiments with my students involvement this summer and publish the results after I have conclusive evidence this whole concept is real. I do know that our disconnect issues went way down after we put these on our robot. I hope this helps other teams, and if you try it and it works I'd like to know that I'm on the right track.


      Frank Bernett (Lead Mentor for Up-A-Creek robotics FTC team 11260)

      Comment


      • #18
        Our team (9915) also participated in the West Super Regional, though we didn't have problems with shutdowns, loss of communication, or other issues. It was pretty wet and relatively warm (50 degrees F) outside in Tacoma, WA, so the humidity was probably not low.

        For those of you looking for ESD surge protectors for usb cables, we found them at:
        http://www.l-com.com/surge-protector...el-mount-style

        At an earlier event (Interleague in Everett, WA in mid-January) it was very cold and dry. We had a lot of issues, most of which we traced to a recently released alpha version of code that now is fixed by more recent releases. But our drive team did notice getting a lot of shocks picking up their robot after each match. We did some investigation, and found threads on the forum discussing the "triboelectric series", which quantitatively represents the tendency of various insulating materials to acquire or donate electrons to one another. Briefly, it turns out the Andymark Stealth Wheels (blue) are pretty much at the opposite end of the triboelectric scale from the materials in the FTC playing field mats. But the buna rubber in the Actobotics Heavy Duty Wheels is much closer to the mat materials. One would expect then, the Stealth wheels to generate more static electricity than the buna rubber ones. We tried running the Stealth wheels with the robot spinning in place on the mat, and our drive team again felt substantial shocks. We immediately replaced those wheels with the buna rubber Actobotics ones, and the intensity of the shocks seemed very substantially diminished. Unfortunately, we did not have an electrometer to do these tests, but perhaps some team with access to one might want to try reproducing our results.

        We decided to stick with the buna rubber wheels for the Super Regional. Prior to the WSR event, we also covered the surfaces of our robot with lexan sheet, though we couldn't cover everything since we still needed to play the game! On the other hand, our wiring is not particularly well isolated from the frame of our robot at all, yet we didn't have problems at our last two events. Our servo and motor controllers are on 3-D printed mounts, but our DIMS and PDM are not, and we have 5 color sensors directly mounted to the metal frame without insulation under them.

        So, I wonder if the teams running the Stealth wheels are having more problems than ones running buna rubber wheels?

        --RoyM
        Coach, FTC9915

        Comment


        • #19
          Is there a lot of static electricity buildup on FRC bots? If yes, does static electricity buildup cause issues for FRC bots?

          Comment


          • #20
            Originally posted by Alec View Post
            Is there a lot of static electricity buildup on FRC bots? If yes, does static electricity buildup cause issues for FRC bots?
            We never have static issues with FRC. First, FRC is playing on carpeted field not foam mat. Secondly, the interconnect of electronics are mainly CAN bus for us and CAN bus is designed for automotive application where it is a harsh environment for electronics. The brain of the robot is RoboRIO which is specifically designed by National Instrument for robotics control purpose. All of these combined to make a rather robust system for robotics application, in my opinion.

            Comment


            • #21
              Frank- Thanks for sharing. Would you be willing or able to send us pictures of the setup you are discussing? I can send you my e-mail address as well if you would like.

              Roy- We purchased one of those surge protectors (The 12" Version since it was the shortest) last week. We just installed it on the USB cable going from the PDM to the phone in hopes that if we have an ESD event on a module that it would prevent that ESD event from getting to the phone and crashing the app or freezing it. Do you use one of those on each module or just on the USB cable going to the phone?

              Thanks!

              Comment


              • #22
                I think this will show the picture of our corona discharge devices



                Here is what we made. They are about 3 inches long and 1 inch wide. The solder keeps them from unraveling.

                Frank Bernett

                Comment


                • #23
                  Frank- The image didn't seem to show up on our end. Can you try attaching it again? Thanks!

                  Comment


                  • #24
                    The forum software just can't handle the link as a picture because it's not directly to a picture but to a web page.

                    Try this link

                    Comment


                    • #25
                      CoachZM,
                      We used just a single one of the LCom surge protectors, in the USB line between the phone and the PDM.
                      --RoyM
                      Coach, FTC9915

                      Comment


                      • #26
                        Thanks for all of the input. We have since added USB surge protection between the PDM and phone. We wipe our robot down with Staticide before each match and make sure the field is sprayed. With those conditions we have had no issues.

                        Our concern for the North Super Regionals is we were just informed that they will be using NO ESD prevention measures on their fields. They are only recommending teams do all they can to prevent ESD themselves. We are now looking into some of the other suggestions from Frank and from past seasons where teams have used Copper tape to help eliminate ESD issues.

                        If anyone has any other suggestions in regards to using copper tape than what we have found online then please share! Thanks!

                        Comment


                        • #27
                          How did the Northern Regionasl work out. Did you beat your ESD problem?

                          Frank

                          Comment


                          • #28
                            We had one ESD issue during a match. All of the others ended up fine. The weather helped a little bit along with wiping our robot down every match with anti static spray and adding the USB surge protector between the PDM and phone. The only frustrating thing is in the event of ESD and the RC Phone App shutting down there is nothing that can be done. From what we were told the FTA's are unable to power cycle the robot in the middle of Tele-Op so there is no way to get the App to open back up on the phone. I would hope in the future something could be written into the App or into the code that would allow the App to restart. Another solution would be is if the robot is in a safe place then the FTA could just power cycle the robot.

                            Comment

                            Working...
                            X