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Unread 04-05-2011, 16:36
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Re: Legally Increasing Motor Performance

Quote:
Originally Posted by JesseK View Post
I heard a rumor from a fellow mentor, who heard it from a well-respected team. It's actually pretty ingenious if it's true, and it's legal as far as I can tell. I'm somewhat skeptical though since I didn't hear the info first-hand and won't have the time to test it for a couple of weeks.

Does running a DC motor in water, specifically a TETRIX motor in de-ionized water, clean out its internal windings enough to noticeably increase its performance? If so, does anyone have relative performance gains?
We definitely ran our motors underwater.

Prior to the Los Angeles regional, we ran our motors on a variable power supply set to 15 volts, current limiting to 3 amps. The motor was run for roughly a hour and a half till its free spin current(comm was coupled to a .25" shaft supported by a Tetrix bushing) dropped under .25 amps.

A couple weeks before the championship event, we heard about the water break in method.. After googling for a bit, we came up with this link(http://www.wattflyer.com/forums/showthread.php?t=7409) in addition to a few youtube videos of RC competitors breaking in their motors underwater.

We went ahead and used a 3 to 1 ratio of deionized water and 99% isopropyl alcohol(helps get rid of the water inside of the motor after we're done with the break in). After submerging the motor underwater, we turned on our variable power supply and let it run at 15 volts for roughly 15 minutes. At the end of the 15 minutes, we dried the motor and put it back on the power supply to measure free spin current. We were able to drop the motor's free spin(without shaft) to 0.09 amps at 15 volts. Attaching the motor to a shaft and running it at 15 volts resulted in having a current draw of 0.18 amps.

We also attached reflective tape to our minibot shafts for testing of motor speeds via contactless tachometer. Without either break in, we were coming out to roughly 9200 RPM at 15V. After the break in, 9800 RPM at 15V.

There was a significant performance increase. I'll post a few videos of our minibots(before and after)...
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Last edited by kiettyyyy : 04-05-2011 at 16:43.
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Unread 04-05-2011, 18:10
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Re: Legally Increasing Motor Performance

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Originally Posted by Chris is me View Post
I've heard from a team that tested such an idea that the gain was not big enough to counteract the magnet weight.
57 discovered that a FP/540 flux ring fits nicely around the Tetrix motor. We thought we were geniuses and fitted out a pair to see if it made a difference, planning on modding the two Tetrix trannies into pseudo flux rings. We didn't see a discernible difference in performance, however. I'm surmising that the rotor is saturated and dumping additional magnetic flux in there isn't going to greatly improve matters.

Quote:
Originally Posted by eagle33199 View Post
We didn't do any real scientific tests to see how motor output changes, but we did try this with a Tetrix motor! Start by hooking up a motor and listening to it. Then add a magnet - you can hear the pitch of the motor change! Moving the magnet around, you can tell that the pitch increases if you're adding to the magnetic field, and decreases if you're subtracting from the field. It's important if trying this to find the "sweet spot". Using a multimeter, we tracked the input current while doing this... using a magnet results in a significant increase in current through the motor, based on our observations. Given the Tetrix motor's enthusiasm for burning out (and their ridiculously high cost), we stopped our experimentation there - no need to encourage them to burn out faster... but it's enough to convince us that you can significantly affect a motor's performance by adding magnets to the casing!
You can certainly affect motor performance with magnets on the case. The question is whether you can significantly improve it or not. You were likely changing the orientation of magnetic flux in the motor as well as changing the strength of it. That would effectively change the brush advance of your motors, changing the performance at high/low speeds. You can tell if you're changing the brush advance of the motor because it will run differently in the forward vs the reverse direction.

The theoretical ideal brush advance changes with rpm and current draw, so it's going to be different at different points on the pole. It'd be really interesting if you could rotate the magnets around the motor as it climbed to change your brush advance dynamically as your bot climbed the pole. Or you could just go with a magnetic minibot + ramp and hit top speed before you even get to the pole.
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Unread 04-05-2011, 18:14
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Re: Legally Increasing Motor Performance

We fooled around with exterior motor magnets and increased the RPMS to 11000. It did counter act the weight on the magnets but the output shaft was spinning so fast that traction became an immediate issue.

It's possible but with what use would it be.
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Unread 04-05-2011, 18:43
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Re: Legally Increasing Motor Performance

When I was into RC Cars, I broke in my motors under water. I always ran the motors at 4.8 volts.

If you are going to attempt this, make sure to clean and oil the motor thoroughly. There are specialty products for cleaning and oiling that are available at most hobby shops.

To be honest, I think your time would be better spent finding inefficiencies in their drivetrain/mechanisms...
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Unread 04-05-2011, 19:42
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Re: Legally Increasing Motor Performance

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Originally Posted by enginerd View Post
To be honest, I think your time would be better spent finding inefficiencies in their drivetrain/mechanisms...
Maybe. But if it helps the minibot motor, why not?

Besides, it's a good task for new members on the team to do.
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Unread 04-05-2011, 19:57
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Re: Legally Increasing Motor Performance

Good point nighterfighter...
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