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  1. #1
    Join Date
    Mar 2004
    Posts
    576

    Help with robot-tower design

    Hi all,

    I'm a mentor for a local high-school's robotics program, participating in the FIRST robotics competions, and I'm new to their team, as the previous mentor moved out of town. I'm really an electronics engineer, but I do have experience with many things mechanical (RC aircraft, cars, my CNC tinkerings, etc).

    After some issues with our robot in a competition last week, we need to re-engineer parts of it quickly for another competition in 3 weeks. And since this will be the last competition with this robot, and we need to keep costs down, I want to re-engineer as little as possible to meet the end goal. Hoping someone here can assist me quickly with some opinions on my proposed changes, as I need to order parts fast.

    The drawing below shows the current setup on the left -- a vertical arm in a tower which is pulled upwards by rubber bands, and triggered/released by a pneumatic actuator. The vertical arm is supposed to hit a large ball (>4ft dia) supported on some overhead rails. The arm can't be higher than the rails (so the robot can pass under), but we're finding that even though we can brush against the bottom of the ball, it's not knocking it off.

    So the redesign (sketch on right) is to use the same arm, and power the arm so it can go up and back down. This way we can get the vertical arm higher to properly knock off the ball, then down to clear the horizontal rails.

    Questions...
    - Should I use a timing belts or a Vee-belts? I would thing Vee, since any resistance/force on the arm (another robot, etc) would just make it slip, rather than break.
    - Is there some thing I can "crimp" or fasten to the belt so that it can easily be secured the dowel for the vertical arm? Or is it acceptable to clamp down on the belt with some screws etc (perhaps with a plate so the screws don't cut the belt)?
    - Any better/simpler/quicker options?

    Thanks,
    -Neil.



  2. #2
    Join Date
    Aug 2005
    Posts
    48
    Hi!
    My English is a somewhat limited, but I will give it a try…
    First of all, imagine a longer rubber band fastened at the bottom of the tower, let it loop trough a wheel as high as possible at the tower and then fasten the rubber band to the lever. you can use the same actuator to release the vertical arm, but with somewhat extended reach and force than in your design. Then, to get the thing back again, a simple string can be looped around a drum on the motor you have in the second example and if the loose end of the string is connected to the lever, you can probably retract the vertical arm again. Eventually, the motor can act as actuator (excluding the pneumatics) just to avoid unexpected knots on the string as it will always be pre-loaded. The motor can this way not “lock” the vertical arm in its upper position and that can be a good thing just to avoid unwanted breaks.
    /jan

  3. #3
    Join Date
    Mar 2004
    Posts
    5
    Neil, hope it is not too late, but I am involved in the program also. I would actually recommend chain. Our robot uses #25 chain and sprockets to raise and lower our shooter. Video here:[ame="http://www.youtube.com/watch?v=JElxKBOT958"]YouTube - Team 1279 2008[/ame]

    You should also spring-load the device to knock off the ball, so it will bend rather than break (or topple the robot) when you hit it on the overhead bar. Our 'bot uses the surgical tubing wrapped PVC pipe to knock off the ball, by brushing underneath.

    What team are you mentoring?


  4. #4
    Join Date
    Mar 2004
    Posts
    576
    Actually yes, it's a bit too late We ended up using the pulley/vee-belt arrangement, and just got it done earlier this week. We had previously tried surgical tubing on the tip of pvc arm, but what we found that the ball got pushed up, then came back down and rested on the same rails. The shape of your robot's vertical arm (with the cross bar) obviously makes a big difference.

    We did not have the funds to enter the 2008 season, but got enough to build a robot to the official spec so we can enter the off-season competitions (I only joined the team after that so I don't have all the details), and we're squeezing funds so we can add it to the next season coming up soon. So, we're just trying to make as few mods as possible now for the last competition next week in Tampa.

    We're team 1889, btw (Palm Beach, FL). I've since discovered the CD forums, so I'll move these discussions over there in the future.

    Cheers,
    -Neil.

  5. #5
    Join Date
    Mar 2004
    Posts
    5
    Neil, best of luck. I am dad1279 over at CD. I know it is tough restarting a team, I did it 5 years ago, with great success.

    You will find the CD forum very active during build season, not so much off-season.

    I tried to send you a PM, but your inbox is full.

    -Alan

  6. #6
    Join Date
    Jul 2006
    Posts
    58
    I was a mentor for Team 975 for about 5 years. I still post on CD occasionally in the tech section.

  7. #7
    Join Date
    Feb 2008
    Posts
    37
    There seems to be a bunch of us around here, I was a student then mentor on #388. If any of you are attending VCU regional this year I will be an inspector there.

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