Legally Increasing Motor Performance

[JesseK]

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?

[Alex Dinsmoor]

Doing a quick search of this on google yielded pretty positive results.

Site 1 Site 2

Apparently it is a known way to "break in" your motors, but not having done it myself I can't speak for the effectiveness. An alternative to this is running the motors at low voltage for a long period of time. (this website has info on that too!)

[Jared Russell]

Related question: If one was to put additional permanent magnets on the exterior of the motor in order to increase the strength of the magnetic field experienced by the armature, what would the expected result be?

No change in speed or torque?
Changing speed into torque (or visa versa) without increasing max power?
An increase or decrease of max power?

I think I know the answer, but I'd like to hear other opinions.

[Chris is me]

I've heard from a team that tested such an idea that the gain was not big enough to counteract the magnet weight.

[Jon Stratis]

Originally Posted by Jared341

Related question: If one was to put additional permanent magnets on the exterior of the motor in order to increase the strength of the magnetic field experienced by the armature, what would the expected result be?

No change in speed or torque?
Changing speed into torque (or visa versa) without increasing max power?
An increase or decrease of max power?

I think I know the answer, but I'd like to hear other opinions.

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!

[sanddrag]

I saw 980 had what appeared to be bare finely stranded copper wire of some sort wrapped around the exterior of their window motor case. I'm wondering what the intended effect was and if they achieved it.

[Al Skierkiewicz]

The effect of running the Tetrix motor under water is to wear in the brushes for more surface contact while keeping the motor cool over a 12-24 hour period. This is a technique used by RC folks and has many references out on the web. The downside is a possibility that the lubricant is flushed out of the bearings and the exposed steel will start to rust. Sealed motors may not benefit the same way the Tetrix motor does. CIM and window motors for instance may not get the cooling where it is needed. FP motors may be harmed due to the circuit breaker attached to the brush assembly.

Use with caution, your mileage may vary.

[kiettyyyy]

Originally Posted by JesseK

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)...

[Kevin Sevcik]

Originally Posted by Chris is me

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.

Originally Posted by eagle33199

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.

[rcmolloy]

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.

[enginerd]

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...

[nighterfighter]

Originally Posted by enginerd

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.

[enginerd]

Good point nighterfighter...

[Coach B.A.D.]

I think it is great that you have the curiousity and drive to improve the motor performance. Under water? Well - after almost 30 years as an engineer - that sends shivers down my spine! When you tested the motor -if the moisture was still in the bearings and or casing that will get in the bearings (and no matter what solvent you use - there is always extra water). Consider that the ease of turning may have been because there may be water in the bearings - however, the water will wear away the bearing finish not to mention the corrosion that will no doubt occur in time and create more friction. The copper commutator contacts will corrode in time and provide resistance in the contact area. Of course, if your motors have as short a life as my 2 FTC teams - well, may not necessarily be a factor.

One question - did you compare the torque before and after while watching the current?

[AdamHeard]

Originally Posted by Coach B.A.D.

I think it is great that you have the curiousity and drive to improve the motor performance. Under water? Well - after almost 30 years as an engineer - that sends shivers down my spine! When you tested the motor -if the moisture was still in the bearings and or casing that will get in the bearings (and no matter what solvent you use - there is always extra water). Consider that the ease of turning may have been because there may be water in the bearings - however, the water will wear away the bearing finish not to mention the corrosion that will no doubt occur in time and create more friction. The copper commutator contacts will corrode in time and provide resistance in the contact area. Of course, if your motors have as short a life as my 2 FTC teams - well, may not necessarily be a factor.

One question - did you compare the torque before and after while watching the current?

In the surprisingly competitive world of RC car racing, this is a very common thing to do.

It improves motor efficiency, and is believed to increase motor lifespans. They make sure to get the water out, and often relube everything.

That being said, most high end rc brushed motors are rebuildable, so it's much easier to clean them out.