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Re: MagLev C

Posted: May 24th, 2013, 5:44 am
by erikb
I will start off saying that the third place robot arm team spent less then $350 total on the arm. Many pieces were scavenged from goodwill buys sush as the thrust bearings from an old drill.

On top of that the biggest expense was having to purchase the transmitters and receivers this year be ause they came up missing from last year. It could have been done this year with less then $100 out of pocket.

So two of the top three robotic arms were not purchased but built with hard work and inginiuty. I am not saying that anyone else did. I am just pointing out that two did not. So don't nit pick

Next, after testing the magnets the kids found that 6 ceramic magnets on a sled and the same type on the track could easily hold 6k. They did not build it because they could not solve the propeller problem

Can their be instances of money buying a win. Sure, it can happen but this year I can assure you it was not the case.

Also, be mindful that not every team that wins purchased their win. Some spent 100 of hours and worked as hard as they could to find the best solution

Re: MagLev C

Posted: May 24th, 2013, 7:01 pm
by plaid suit guy2
if the vex parts hadn't been vex quality, we wouldn't have blown up those motors, and the robot would have been like $100
the bulk of the cost was in the zip ties, the duct tape, and the rivets, everything else was scavenged or borrowed.

Re: MagLev C

Posted: May 29th, 2013, 8:29 pm
by gorf250
@jdog:
where did you get those propellers? like no one sells them
gws propellers glued together, so it's a 6 bladed prop.
Jdogg, why did you choose to make your rear prop so small?

Re: MagLev C

Posted: May 29th, 2013, 9:32 pm
by hmcginny
@jdog:
where did you get those propellers? like no one sells them
gws propellers glued together, so it's a 6 bladed prop.
Jdogg, why did you choose to make your rear prop so small?
Space concerns (needed to use as much space as possible for weight), and trying to generate more thrust in the area close to the rotational axis, where the large prop wasn't creating much. Also partially because we had the small propeller already attached from an older design.

Re: MagLev C

Posted: May 29th, 2013, 9:42 pm
by Jdogg

Space concerns (needed to use as much space as possible for weight), and trying to generate more thrust in the area close to the rotational axis, where the large prop wasn't creating much. Also partially because we had the small propeller already attached from an older design.
yeah, what he said :)

Re: MagLev C

Posted: June 2nd, 2013, 12:34 pm
by GeoChamp96

Space concerns (needed to use as much space as possible for weight), and trying to generate more thrust in the area close to the rotational axis, where the large prop wasn't creating much. Also partially because we had the small propeller already attached from an older design.
What advantage would having more thrust closer to the rotational axis give you (as opposed to farther out)? More stability?

Re: MagLev C

Posted: June 2nd, 2013, 3:08 pm
by Jdogg

Space concerns (needed to use as much space as possible for weight), and trying to generate more thrust in the area close to the rotational axis, where the large prop wasn't creating much. Also partially because we had the small propeller already attached from an older design.
What advantage would having more thrust closer to the rotational axis give you (as opposed to farther out)? More stability?
What hmcginny was getting at is that the front propeller produces some thrust over the 6inch propeller's diameter let's call this it's thrust density. The smaller prop produces a larger thrust density than the larger prop even though the larger prop produces more overall thrust. So with that specific combination we had, we were able to get the front's propeller's thrust for the area that is outside the smaller propeller's thrust but still maximize the overall amount of thrust for the maglev.
Common misconception is having two propellers behind each other will produce more thrust, that is not necessarily correct. Due to the fact that the air behind the front propeller is already moving at some speed relative to the maglev.
So all in all, we tried to produce the greatest thrust behind the entire maglev and since the smaller blades had a larger thrust density than that of the larger blade we put the motor behind the front motor. This also kept the aerodynamic properties of our maglev as close to intact as possible.

Re: MagLev C

Posted: June 2nd, 2013, 9:51 pm
by cantthinkofausername
In response to anyone who is concerned about a stopping mechanism, you can always reverse the polarity of magnets at the very end of the track you're using it would make the Mag Lev just stick down and stopping immediately instead of flying dangerously off of the track or into a barrier that may damage it. Unless your propellers are huge that, than I don't know how to make this work without breaking the propellers.

Re: MagLev C

Posted: June 5th, 2013, 11:56 am
by GeoChamp96
In response to anyone who is concerned about a stopping mechanism, you can always reverse the polarity of magnets at the very end of the track you're using it would make the Mag Lev just stick down and stopping immediately instead of flying dangerously off of the track or into a barrier that may damage it. Unless your propellers are huge that, than I don't know how to make this work without breaking the propellers.
It's also possible that next year's rules will include a defined way to stop the car at the end of the track as part of those "significant adjustments" the Chalkers were talking about. It could be anything from a physical barrier to reversed magnets to a kill switch at the front of the vehicle. Or maybe a combination of several methods.