MagLev C

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JTMess
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Re: MagLev C

Post by JTMess » February 26th, 2013, 7:18 pm

blakinator8 wrote:
JTMess wrote:We are experiencing a problem where our motors slowly go from full thrust to not working at all in a period of ~15 seconds. They are connected to 40C batteries, which may be melting or breaking components in the motor... does anyone know why this problem may be occurring or how to remedy it?
We had a problem where the propeller would not stay on the shaft of the motor. Does it make a high pitch whining noise or just shut off completely?
The propeller is definitely staying on the shaft properly. The rpm's start very high then gradually decrease over like 15 seconds until the motor won't turn at all, as if resistance is being added or voltage is decreasing very rapidly.
2014 States: Scrambler-2nd, Mission Possible-2nd, Experimental Design-3rd, Circuit Lab-3rd
2014 Regionals: Scrambler-1st, Mission-1st, Technical Problem Solving-1st, Circuit Lab-1st, Maglev-1st, Bungee Drop-1st
2013 States: Gravity Vehicle-1st, Fermi-8th, Maglev-1st

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Re: MagLev C

Post by mrsteven » February 26th, 2013, 7:22 pm

That is an annoying problem, if you havent keyed out your shaft, you should do that for a set screw to nest better.

Its possible that your battery isnt producing enough current for the motor and your going through it all before you actually do much of anything. 40C is relative on the voltage of the battery pack and if its actually 40C or 40C burst. If the motor wants to draw more amps than the battery will provide and thus the motor is using the batteries burst current rating, then after that time, youll see it go down since the battery isnt meant to discharge at burst for extended periods of time. Hook up the motor to the set voltage to a variable power source and see how many amps your motor wants to draw. Mine is around 10 amps

Not sure what motor you're using, but I'm using a good sized r/c motor for my car with 65C batteries and I have no problem with "melting or breaking components"

EDIT: I also had a problem similar, when I was just testing my motor I plugged it into a random 7.4v battery (it was low current) it would spin for a bit, slow, then stop. When I put the actual batteries I'm using now on it, it worked since it has sufficient current, I suspect
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JTMess
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Re: MagLev C

Post by JTMess » February 26th, 2013, 7:42 pm

It is 40C continuous, though we're concerned we might actually be using too much current. We disconnected the batteries and connected a 9V that was unable to make the motor turn, although it had been able to previously, leading us to believe the motor may be fried.
2014 States: Scrambler-2nd, Mission Possible-2nd, Experimental Design-3rd, Circuit Lab-3rd
2014 Regionals: Scrambler-1st, Mission-1st, Technical Problem Solving-1st, Circuit Lab-1st, Maglev-1st, Bungee Drop-1st
2013 States: Gravity Vehicle-1st, Fermi-8th, Maglev-1st

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Re: MagLev C

Post by joeyjoejoe » February 27th, 2013, 4:32 am

Is the voltage provided by the battery within the tolerances of the motor? Such a battery capable of providing even 100 amps wouldn't fry the motor. The motor is simply a load on the battery and, provided the voltage is correct, will use the current it "needs" electrically speaking.
After it spins down, can you just wait a while (no recharging the battery) and reconnect it to the motor and have it work again? If so, I'd say you have a battery problem. Maybe it's overheating. I suppose you could have a connection problem. Verify that you are using a good gauge wire (18 gauge is what we use) and that all connections are well soldered. If you are using any non-soldered connections (wire nuts, bread board etc) I would get rid of them. Anything that could be a current bottleneck should be removed. On one of our first cars, one of our students noticed that the switch got very hot after an afternoon of testing. I decided we should replace it with a "beefier" switch for safety's sake. When we did that, the motors made a much louder, higher pitch sound when they were turned on and all of our times were much better! I believe that the switch was limiting the current to the motor and was therefore a load upon the battery as well.

BTW, we have motors with an operating voltage of 7.2-8.4v. We use just two 3.7v (actually 4v) 14500 (1000mah) batteries in series which provide 8v total to the motor. Our motors will run for minutes at a time before the batteries start dropping to the 7.5v range and our times start getting affected.

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Re: MagLev C

Post by JTMess » February 27th, 2013, 7:39 am

joeyjoejoe wrote:Is the voltage provided by the battery within the tolerances of the motor? Such a battery capable of providing even 100 amps wouldn't fry the motor. The motor is simply a load on the battery and, provided the voltage is correct, will use the current it "needs" electrically speaking.
After it spins down, can you just wait a while (no recharging the battery) and reconnect it to the motor and have it work again? If so, I'd say you have a battery problem. Maybe it's overheating. I suppose you could have a connection problem. Verify that you are using a good gauge wire (18 gauge is what we use) and that all connections are well soldered. If you are using any non-soldered connections (wire nuts, bread board etc) I would get rid of them. Anything that could be a current bottleneck should be removed. On one of our first cars, one of our students noticed that the switch got very hot after an afternoon of testing. I decided we should replace it with a "beefier" switch for safety's sake. When we did that, the motors made a much louder, higher pitch sound when they were turned on and all of our times were much better! I believe that the switch was limiting the current to the motor and was therefore a load upon the battery as well.

BTW, we have motors with an operating voltage of 7.2-8.4v. We use just two 3.7v (actually 4v) 14500 (1000mah) batteries in series which provide 8v total to the motor. Our motors will run for minutes at a time before the batteries start dropping to the 7.5v range and our times start getting affected.
We are using quite similar batteries, although they are 1800mAh each. Upon closer inspection with a voltmeter, we definitely have a battery problem. The voltage readings on both batteries dropped from 8.2V to less than 2V in a matter of seconds.
2014 States: Scrambler-2nd, Mission Possible-2nd, Experimental Design-3rd, Circuit Lab-3rd
2014 Regionals: Scrambler-1st, Mission-1st, Technical Problem Solving-1st, Circuit Lab-1st, Maglev-1st, Bungee Drop-1st
2013 States: Gravity Vehicle-1st, Fermi-8th, Maglev-1st

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Re: MagLev C

Post by mrsteven » February 27th, 2013, 5:35 pm

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Lake101258
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Re: MagLev C

Post by Lake101258 » February 27th, 2013, 9:29 pm

Has anyone tested to see whether the rectangular ceramic magnets or the strip magnets from Kelvin are better?

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Re: MagLev C

Post by wlsguy » February 28th, 2013, 5:16 am

Lake101258 wrote:Has anyone tested to see whether the rectangular ceramic magnets or the strip magnets from Kelvin are better?
The ceramic magnets have more lift but also have more weight. I don't know the weight / lift ratio of each but would suspect the ceramic magnet is more powerful.

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Re: MagLev C

Post by ohiostar » February 28th, 2013, 6:23 am

chalker wrote:FYI, we posted a new clarification for MagLev today: http://soinc.org/official_rules_clarif
Out of curiosity, have any incidents of injury (hopefully noting more than a band aid) been reported to warrant the rule clarification. I have seen some students jerk their hands back away from the vehicle. It was obvious that they had inadvertently touched the spinning blade. Thankfully no harm occurred.

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Re: MagLev C

Post by wlsguy » February 28th, 2013, 7:35 am

Our team had 2 band-aid incidents this season.
In both cases it was due to careless errors.
I learned (as the coach) to never try and keep the vehicle from running off of the table using your hand.
Yes, it made the kids laugh (they knew better) but inspired me to make a stop for the end of the track so it could not occur.
Our vehicle now hits a bumper at the end of the track to keep it from running away.

Also, one thing to consider if I was writing the rules for next year would be to require a kill switch and so the vehicle blades automatically stop at the end of the run. I would allow this part to exceed the dimensions.

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