MagLev C

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MagLev C

Postby Jim_R » July 31st, 2013, 8:32 am

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Re: MagLev C

Postby GeoChamp96 » September 9th, 2013, 7:46 am

So, it says in the rules that the vehicle must hit a target time between 5 and 15 seconds for 95cm. This may just be me being relatively inexperienced, but how are you supposed to slow down the run time without changing the mass of the vehicle? That seems kind of impossible...

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Re: MagLev C

Postby chalker » September 9th, 2013, 9:13 am

GeoChamp96 wrote:So, it says in the rules that the vehicle must hit a target time between 5 and 15 seconds for 95cm. This may just be me being relatively inexperienced, but how are you supposed to slow down the run time without changing the mass of the vehicle? That seems kind of impossible...


I don't see anything in the rules prohibiting you from changing the mass of the vehicle....

And there are lots of other ways to approach this problem. A couple ideas off the top of my head (and by no means exhaustive): adjust the speed of the propeller, adjust the pitch of the propeller, change the direction of thrust relative to motion, partially block the intake to the propeller, induce some friction with the siderails.

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Re: MagLev C

Postby twototwenty » September 10th, 2013, 5:40 am

A very easy way to do this: potentiometer. Done and done.

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Re: MagLev C

Postby JTMess » September 10th, 2013, 8:36 am

GeoChamp96 wrote:So, it says in the rules that the vehicle must hit a target time between 5 and 15 seconds for 95cm. This may just be me being relatively inexperienced, but how are you supposed to slow down the run time without changing the mass of the vehicle? That seems kind of impossible...


I must say that I'm very disappointed with this change in the rules. I think going for a target time really takes the "racing" spirit out of the event.
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Re: MagLev C

Postby iwonder » September 10th, 2013, 8:38 am

I think that was the idea :P

Admittedly, it's not as exciting now, but still interesting.
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Re: MagLev C

Postby FawnOnyx » September 10th, 2013, 8:49 am

I in general like the changes they made, such as guards for propellers, and no need to go for the most power or mass. I do think that 5 to 15 seconds is a really slow target time range to move a max 2kg maglev just a meter though.

twototwenty wrote:A very easy way to do this: potentiometer. Done and done.

I'm not sure, but wouldn't this cause heat dissipation problems when you resistively current limit the motor? I think most pots are rated for 1/4-1/2 watts, so even for 15 seconds wouldn't it overheat and blow?
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Re: MagLev C

Postby iwonder » September 10th, 2013, 8:54 am

Most pots don't have the power rating for this event, but some are rated for much high power. Just remember, it's not the power from the motor, it's the power that's lost in the resistor, they're typically a large difference.
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Re: MagLev C

Postby Schrodingerscat » September 10th, 2013, 8:58 am

It seems to me that while precisely meeting the time will be challenging without the danger, the magnetic levitation is now just a formality instead of an advantage when working properly, as I am pretty sure from experience last year that one could make 5 seconds sitting on the floor with a decent motor and prop combo.

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Re: MagLev C

Postby GeoChamp96 » September 10th, 2013, 9:33 am

JTMess wrote:
GeoChamp96 wrote:So, it says in the rules that the vehicle must hit a target time between 5 and 15 seconds for 95cm. This may just be me being relatively inexperienced, but how are you supposed to slow down the run time without changing the mass of the vehicle? That seems kind of impossible...


I must say that I'm very disappointed with this change in the rules. I think going for a target time really takes the "racing" spirit out of the event.


I agree that the event isn't quite as exciting as it was last year, but it was kind of necessary. The rich teams had a huge advantage and the teams with smaller budgets were kind of stuck.

This way, you don't just go and buy the biggest 9V motor you can find and run it with 3000mAh LiPo

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Re: MagLev C

Postby erikb » September 10th, 2013, 9:55 am

FawnOnyx wrote:I in general like the changes they made, such as guards for propellers, and no need to go for the most power or mass. I do think that 5 to 15 seconds is a really slow target time range to move a max 2kg maglev just a meter though.

twototwenty wrote:A very easy way to do this: potentiometer. Done and done.

I'm not sure, but wouldn't this cause heat dissipation problems when you resistively current limit the motor? I think most pots are rated for 1/4-1/2 watts, so even for 15 seconds wouldn't it overheat and blow?

There is more then one way to fry a chicken.

Yes, you are going to have a hard time finding a pot that works for this situation. But rheostats are common and cheap.
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Re: MagLev C

Postby chalker7 » September 11th, 2013, 10:40 am

GeoChamp96 wrote:I agree that the event isn't quite as exciting as it was last year, but it was kind of necessary. The rich teams had a huge advantage and the teams with smaller budgets were kind of stuck.

This way, you don't just go and buy the biggest 9V motor you can find and run it with 3000mAh LiPo


I have said this before and I will say this again, money does not buy a winning device. Instead, I encourage you to think of the issue this way: resources contribute to and enable performance. The distinction between money and resources is critical, money is a resource but it isn't the only variable. Teams with more resources like time, access to professionals/equipment, expertise, experience, etc will also produce a quality device even if they don't necessarily have large budgets.

Similarly, don't think of performance simply as the fastest/longest flying/lightest/whatever is relevant one year. Consistency is also a performance metric. A team that professionally mills their chassis out of billet aluminum and has a custom circuit trace etched for their motor/battery is going to have a much more predictable and consistent time than a team that duct tapes cardboard together and twists their wires. In the former case, resources help enable the creation of such a device.

Finally, I don't want to be difficult, but a 3000mAh LiPo means effectively nothing for overall performance, that's just how much charge the battery can carry. What really matters (or mattered) in this event is how quickly it can discharge and how evenly it can discharge. Those ratings are the "C" ratings on a battery. A tiny 100mAh battery rated at 70C would outperform a huge 3000mAh battery rated at 15C in a short race. However, you could get many more runs (30 more, to be precise) out of the big battery. The people who work on these rules do know what they're talking about...sometimes... :)
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Re: MagLev C

Postby erikb » September 11th, 2013, 12:50 pm

GeoChamp96 wrote:The rich teams had a huge advantage and the teams with smaller budgets were kind of stuck.


Stuck how? Winning comes down to who looks at the problem and comes up with the best solution. Then works hard at implementing that solution.

When you start out thinking that you can't win because of some reason you won't.

Last year Poudre placed 1,2,3,6 and 9 at nationals, in the build events. And less $100 was spent building the device for each event. The kids had to scavenge and recycle. Only the robotic arm received more and that was because the transmitters and receivers vanished over the summer.

And their was no fancy milling. The mag lev was balsa wood glued to magnets and motors. The track was stolen magnetic strips from a chalk board (we did offer to give them back after nationals) and left over wood from someone's wood project.

It's the solution and the time you put in that wins. Not if you can purchase it.
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Re: MagLev C

Postby GeoChamp96 » September 11th, 2013, 8:57 pm

chalker7 wrote:
GeoChamp96 wrote:I agree that the event isn't quite as exciting as it was last year, but it was kind of necessary. The rich teams had a huge advantage and the teams with smaller budgets were kind of stuck.

This way, you don't just go and buy the biggest 9V motor you can find and run it with 3000mAh LiPo


I have said this before and I will say this again, money does not buy a winning device. Instead, I encourage you to think of the issue this way: resources contribute to and enable performance. The distinction between money and resources is critical, money is a resource but it isn't the only variable. Teams with more resources like time, access to professionals/equipment, expertise, experience, etc will also produce a quality device even if they don't necessarily have large budgets.

Similarly, don't think of performance simply as the fastest/longest flying/lightest/whatever is relevant one year. Consistency is also a performance metric. A team that professionally mills their chassis out of billet aluminum and has a custom circuit trace etched for their motor/battery is going to have a much more predictable and consistent time than a team that duct tapes cardboard together and twists their wires. In the former case, resources help enable the creation of such a device.

Finally, I don't want to be difficult, but a 3000mAh LiPo means effectively nothing for overall performance, that's just how much charge the battery can carry. What really matters (or mattered) in this event is how quickly it can discharge and how evenly it can discharge. Those ratings are the "C" ratings on a battery. A tiny 100mAh battery rated at 70C would outperform a huge 3000mAh battery rated at 15C in a short race. However, you could get many more runs (30 more, to be precise) out of the big battery. The people who work on these rules do know what they're talking about...sometimes... :)


Perhaps I phrased that poorly. I was thinking about many of the teams I saw with rare earth tracks and >3kg cars, and how some teams don't necessarily have the same amount of resources (ours, for example. There's no way we would have spent the close to $1,000 some of those tracks can cost). Yes, I know there were many other ways to come up with a good score, but having it be a set time seems to me to be more accessible to all the teams. But hey, I don't know much. It's only my second year in the event.

The point I was trying to make with the batteries is that the 3,000mAh ones are generally more expensive than ones with less capacity of the same brand. Perhaps I phrased that pretty poorly as well. I apologize.

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Re: MagLev C

Postby gorf250 » September 11th, 2013, 10:38 pm

iwonder wrote:Most pots don't have the power rating for this event, but some are rated for much high power. Just remember, it's not the power from the motor, it's the power that's lost in the resistor, they're typically a large difference.


Based on some super quick (and probably mildly incorrect) calculations using the fact that my maglev drew about 20A last year, and a vehicle this year will need to draw about 4 amps (twice the mass, but ten times slower, I realize that these relationships probably aren't linear but close enough) we can roughly calculate the power consumed by the potentiometer. Using the formula P=I^2 R, a potentiometer with a resistance of around 2.5 ohms would consume about 40W. Plus you would need a pot with an extremely low resistance to avoid drawing all the power in the circuit. Sorry if my calculations are blatantly wrong.
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