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Re: Robot Arm C

Posted: May 19th, 2013, 9:43 pm
by iwonder
I think you're right about the pressure, Jdogg. And I wish I had thought of the winch servo in time... oh well.

Re: Robot Arm C

Posted: May 19th, 2013, 9:45 pm
by plaid suit guy2
Tie it to a weight with a slip knot, push it into the north, drop the ball into a cup that has a hole in the bottom big enough to let the ball touch the floor, therefore the ball is in the north zone and at it's starting height, open up the knot and watch the balloon and ball float away. If time stops, grab the string's spool with the arm, and the balloon will stop. Measure the bottom of the ball through the hole in the cup.

For the storage issue, one can make hydrogen quickly by mixing Zn and HCl, fed into the balloon, and then something to stop the hydrogen from escaping.

Re: Robot Arm C

Posted: May 19th, 2013, 9:48 pm
by Jdogg
Tie it to a weight with a slip knot, push it into the north, drop the ball into a cup that has a hole in the bottom big enough to let the ball touch the floor, therefore the ball is in the north zone and at it's starting height, open up the knot and watch the balloon and ball float away. If time stops, grab the string's spool with the arm, and the balloon will stop. Measure the bottom of the ball through the hole in the cup.

For the storage issue, one can make hydrogen quickly by mixing Zn and HCl, fed into the balloon, and then something to stop the hydrogen from escaping.
hmmm.. yeah I think you might be able to build something to make it all work. But then again HCl is a dangerous substance. Plus trying to create enough helium and push it into a ballon is pretty hard to do in 3 minutes and pretty hard to do at all. If someone actually built that using safe chemicals and made it score a point, that would be truly awesome :).

Re: Robot Arm C

Posted: May 19th, 2013, 9:52 pm
by mrsteven
Emphasis on SAFE
*que general rule number something that says students may not bring unsafe devices*
Number 5 perhaps?

Re: Robot Arm C

Posted: May 19th, 2013, 10:07 pm
by iwonder
Yeah... sustaining a Zn + HCl reaction to generate enough hydrogen to pressurize and fill a balloon is a major feat by anyone, and to do it in a small enough space as a robot arm... Not to mention, not only did you start with HCl(highly concentrated most likely), but no you've got a balloon full of H2, which is highly flammable. Neither one seems very safe to me :P

Re: Robot Arm C

Posted: May 19th, 2013, 10:18 pm
by mrsteven
Yeah... sustaining a Zn + HCl reaction to generate enough hydrogen to pressurize and fill a balloon is a major feat by anyone, and to do it in a small enough space as a robot arm... Not to mention, not only did you start with HCl(highly concentrated most likely), but no you've got a balloon full of H2, which is highly flammable. Neither one seems very safe to me :P
floating up towards very hot, incandecent light bulb fixtures...

Re: Robot Arm C

Posted: May 20th, 2013, 6:30 am
by harryk
Yup, winch servo all the way :) that's how I did it.
Winch servo club!!! Though I used mine with a set of gears to reduce it and add more torque

Re: Robot Arm C

Posted: May 20th, 2013, 7:16 am
by jander14indoor
From the horse's mouth.
The winning device. The MOTOR that raised the ball on the tape mechanism provided the power to rotate the general purpose arm into the the north zone for a pipe. Scoring a point. The general purpose arm (which scored many points,no issue there) started the ball at ground level, RAISED it to the tape mechanism. The tape mechanism's motor (that had moved an object into the north zone other than the ball) then RAISED the ball further. All meeting the literal words of the rules.

Balloons.
Zero gage pressure. Pressure equal to atmospheric. Rubber balloons have positive gage pressure if the membrane is stretched. Mylar balloons are a little problematic. IF the membrane is taught, again positive gage pressure. If loose, zero gage pressure. That's how the one balloon at nationals was allowed to compete in tier one. Open bottom balloon (hot air balloon) is naturally zero gage pressure since it is directly open to atmosphere.

Previously scoring a point with a balloon. There are many solutions, here's one. Wrap the balloon tether around the wheel of a wheel and axle. Hold the balloon down by grabbing the tether short with two clamps. Attach the axle to a mechanism to push balls and nails into the north zone. Release first clamp to allow balloon RISE a short distance and power mechanism to push balls and nail forward. General purpose arm scores all the points but one ball. Last action, general purpose arm lifts last ball into balloon basket. Second clamp releases tether (final end still attached to robot) to allow the balloon to continue RAISING the ball as high as the tether rises. The balloon provided the energy to score points and then provided the energy to RAISE the ping pong ball.

Back to the one balloon in the tournament. Frankly I don't know HOW they intended to score a point prior to raising the ball. They tried to explain something, I wasn't convinced, but was willing to suspend judgement and watch. Fortunately for me, for other reasons they never attempted the balloon task so I didn't have to make a decision.

plaid suit guy2's proposal. Hmm, not clear how the balloon rising scored the point. Better make sure that floating ballon stays OVER the north zone at the end.

Note, this difficulty of deciding on the details of compliance is why we event supervisors refuse to decide or rule on such issues without seeing the device. Its why when I offer statements I couch them as OPINIONs.

Yeah, the Zn HCl idea. Aside from the issues of getting a balloon to score the previous point, I'd probably stop such an approach from a pure safety point of view. The general safety rules give me a LOT of discretion to rule in that area. And I'm not likely to be over ruled by the arbitration committee on safety.

Overall, I saw a lot of really great approaches over the last two years, met a lot of great students & coaches. As we retire Robot Arm in div C for a while, thanks for the experience.

Jeff Anderson
Still in Beavercreek, OH for the State Director's meeting, though perhaps not fully engaged in the meeting...
Normally, Livonia, MI

Re: Robot Arm C

Posted: May 20th, 2013, 9:15 am
by olympiaddict
Same here, harryk :) Although given more time, I would've changed it to a regular high-torque servo with the potentiometer externalized to get the needed range and gearing- I didn't like having to trick the PID loop of my servo in order to get it to move fast enough.

Mr. Anderson, would you be able to give us any more information, qualitative or quantitative, about the points distribution, etc., from this year at Nationals, and how it compares to Robot Arm last year and/or other events you've been involved with?

Wait, jdogg, I was re-watching your video, and I recalled that you mentioned a "tape measure" device- do you mean to say that the yellow part of your height bonus that makes the extension happen is all supported by tape measure? Because if so that's absolutely brilliant! :)

Re: Robot Arm C

Posted: May 20th, 2013, 9:41 am
by Jdogg
Same here, harryk :) Although given more time, I would've changed it to a regular high-torque servo with the potentiometer externalized to get the needed range and gearing- I didn't like having to trick the PID loop of my servo in order to get it to move fast enough.

Mr. Anderson, would you be able to give us any more information, qualitative or quantitative, about the points distribution, etc., from this year at Nationals, and how it compares to Robot Arm last year and/or other events you've been involved with?

Wait, jdogg, I was re-watching your video, and I recalled that you mentioned a "tape measure" device- do you mean to say that the yellow part of your height bonus that makes the extension happen is all supported by tape measure? Because if so that's absolutely brilliant! :)
Yeah 2/5 tape measures I'll post a video of it going to like 20 feet later this week. It's pretty cool and fast, I can go to 20 feet in about 40 seconds or so. Though it loses stability at like 16 ish feet. I saw a few others tape measure devices too, I think ours was pretty cool because it used this little 3d printed parts that were pushed up by the tape measures to stabilize it every 1 foot to 2.5 feet later on.