MagLev C

[iwonder]

Ahh, so here's your first problem...

.35Ah * 25 = 8.75Ah, so you're exceeding the batteries ratings by even drawing that much current from it. I'm surprised the internal resistance even allows 17A to be drawn from it.

And, .35/17 = .02059 hours, or about 1 minute and 14 seconds that the battery could possibly handle the load you're putting it under, so I assume when you say it dies quickly, it dies within 2 or 3 runs?

So let's find a battery that would work... You've probably got a different selection of batteries but this should work for demonstration.
You need to be able to discharge the batteries at 17Ah(the unit of time doesn't matter, actually, but since batteries are rated in mAh, hours is easiest). Looking at some batteries online, most are rated for 25C, that's at least a 680mAh battery that can be discharged at 25C(C refers to the capacity of the battery).

[iwonder]

Our motors have a DC resistance of around .8 ohms. Since you mentioned melted wires and motors, I'd expect you have a motor problem. What kind of motors are you using? Even the cheapest hobby store dc motors under 3.5cm in diameter shouldn't pull more than around 10 A (or at least not for very long). Also, you are breaking the circuit to measure current, right? I still stand by my original statement that 10+ DC amps is too high for the small motors we are allowed to use for this competition.
Iwonder: Not sure that setup would be legal for the competition .

Sorry for the double...

We're talking about RC grade motors(at least I am) which are a different breed than the hobby store small electric motors(https://www.sparkfun.com/products/10171), these motors(http://www.rchobbyexplosion.com/Venom_G ... en1301.htm) can, in fact, pull upwards of 10A(one of mine will pull 18A at 8.2v, but the high voltage(therefore speed) will destroy the motor quickly, the 10A number is two in series.

And I think the first problem with that setup is my school's lack of SO funding

[joeyjoejoe]

I will have to look at the motor more thoroughly (no specs re current on the site you list) but I'll say it again, If you run a motor at the voltage it was designed to run at, it should not exhibit the problems listed in these posts.

As for the SO funding comment, dont get me started! The four events I am coaching are funded just as well as my personal credit card says they are.

[mrsteven]

Oh same man. Robot arm and maglev are both on my dime. Our funding only covers gravity vehicle. Servos are expensive >.>

Im using a similar motor to the fireball one listed on that link, and im getting 15A on start up and 10A regular without load. With prop i imagine it also to be around 12-15

[joeyjoejoe]

OK. I just measured the current of our existing motor/prop (i.e. under full load) and here are the results:
1. The sound was almost too loud to talk over.
2. The breeze blew my pencil cup full of pencils off of my desk.
3. I had to tape the car to my desk so that it wouldn't fly off.
4. The current pulled was a scant 3.2amps.

If more current translates to more power (and it should) I sure hope that my team doesn't have to face those of you with motors pulling 5 times this amount.

[cnapun]

Our EDFs pull about 10A-15A each, but the thrust is relatively low (only about 1N apiece); they're rated for 8.5 oz at 11V, and lowering that to 9.9V shouldn't have too much of an effect on it.
On a completely unrelated note, does anyone know how to make a good duct?

[blakinator8]

but the thrust is relatively low (only about 1N apiece);

Have you had success building a rig to test the force, or are you just measuring the pull of the vehicle?

On a completely unrelated note, does anyone know how to make a good duct?

I've seen free models online for 3D printing, if you have that capability.

[iwonder]

Hmm, that makes me want to measure the thrust my vehicle produces

And why the ducted fans? The diameter limit seems like it doesn't make it worth it.

[cnapun]

but the thrust is relatively low (only about 1N apiece);

Have you had success building a rig to test the force, or are you just measuring the pull of the vehicle?

I'm estimating based on the motion of a cart along a track

And why the ducted fans? The diameter limit seems like it doesn't make it worth it.

They were very cheap and rated for pretty high thrust, and you can fit 2 on a vehicle. I also like the increased sense of safety with no open propellers, although my fan did rip a hole in my sweatshirt.

[blakinator8]

And why the ducted fans? The diameter limit seems like it doesn't make it worth it.

I agree that they feel safer, and they are are also more modular and easy to mount. They also can be positioned lower to keep a low center of gravity.