A Guide To Breaking In Your Brushed Electric Motors (Seating The Brushes)
Short version:
If you don’t want to read this lengthy post and you just want to know how to get to it, take your motor and hook it up to 1/3 to 1/2 the operating voltage for 1 to 2 hours, and it helps if you break-in the motor going the same direction as it will be turning when you attach it to your RC. Basically what this amounts to is taking 2 alkaline AA’s and hooking them in series to your motor and allowing the batteries to run dead (for 2 or 3s lipo’s, and 6 to 8 cell NiMH’s and NiCD’s). Dry break-in’s are probably the best (if you would like to see the reasoning for this see the section Types of Break-in’s).
So what is a break-in process anyway?
Looking at the pictures you can see there are brushes (they aren’t really brushes, but actually just carbon blocks), and a commutator. Basically, what we want to do is take the square shape of the brushes and wear it into the round shape of the commutator under a low-voltage, no-load situation. It should also be noted that brushless motors do not really require a break-in because they do not have brushes, and instead work on FM (frequency modulation, a type of a/c power), and brushed motors work on current regulation through voltage (current is directly correlated with voltage, if the resistance stays the same, and the voltage goes up, then the current will go up also). Also some of the high performance RC brushes (like in buggies, cars and trucks) have serrated edges, which are supposed to either reduce or completely eliminate break-in.
How does it help?
What this does is allow the brush to more fully contact the commutator over a wider area (effectively reducing motor resistance consequently increasing motor power), which reduces the amount of electricity that flows through a given piece of the brush. This in turn reduces resistance and arcing between the bushes and the commutator (as the current is transferred to the commutator over a wider contact point), which also alleviates the microscopic pitting, excessive carbon soot buildup, and excessive heat build up. All of this in turn makes the motor last longer, be more reliable, and draw current more predictably and run more efficient (see note at the end), which results in better and longer battery life.
The carbon soot is non conductive, and adds resistance to a motor, which causes it to heat more (where the resistance is, which can cause the brushes to fuse to the commutator), and loose power (because energy is being wasted in resistance (in the form of heat) before it ever even gets to the motor windings). This carbon buildup can also cause shorter flight times, and in more rare, but more serious cases can cause damage/burn-out to your ESC (3 or 4 in 1) by causing current spikes, and it could also damage batteries with the extra current in certain more unlikely situations.
The arcing in the motor over a smaller surface area, such as using a motor that has not been broken in, causes more electricity in a smaller area of the brush, which causes more heat in that particular area, which basically burns the carbon brushes creating the high resistance carbon soot, and also creates microscopic pits in the commutator and brush where the electricity arced from and to. This basically creates microscopic sand paper that also contributes to the early demise of the motor. This is a double drawback because it consumes the brushes faster, and causes pitting and carbon buildup which reduces the power of the motor, the battery life, and causes excessive heating in the motor which can fuse the brushes to the commutator.
Types of Break-in’s: Wet or Dry, Why or Why Not?
I have heard several explanations of the break-in process, and some of them involve putting the motor in water, rubbing alcohol or some other liquid, or surrounding them in ice to keep them cool. There are a few reasons to do some of these, and a few reasons not to.
First let’s start with water. The main reasons I have heard to do the break-in in water is to reduce pitting during motor arcing in the break-in, and to keep the temperature down low, and wash away the carbon buildup during break-in. I also cannot confirm this, but I have heard that water break-in’s result in a higher performance motor that doesn’t last quite as long as a dry break-in (more info to come*).
To dispel some myths about water break-in’s, no it will not short circuit, nor will it fry the motor, or over current the batteries or whatever you are using to break-in your motor. To test this for yourself take an ohm meter and place the probes in the water, and vary the distance between them. You will see that the ohm reading is quite high, though it still conducts electricity. Also it should be noted that pure water is among the best insulators on the planet. It is just the ion and particles dispersed in the water that conduct the electricity (such as lime calcium magnesium and salt).
One thing to note with a water break-in however is that it is best to use distilled water if you are going to use water to break-in your motors. The reason for this is because regular water or hard water can leave a residue of minerals on the motor parts, which could cause undesirable performance, or corrosion, and it does not conduct electricity.
Another thing to note with the water break-in is that there are small nooks and crannies in DC motors for water to stay, and over time rust and corrode the inside of the motor. These places include the spaces between the commutator, between the commutator and the armature windings, where the armature meets the shaft, in between the plates of the armature, and so on. All the water needs to be forced out somehow. Taking the motor apart is not preferred because it can change how the brushes seat, effectively reducing your break-in. A lot of people use compressed air, especially the motors with a hole in the side of the can. Obviously the smaller motors are much harder to get the water out of.
*Wet break-in’s as I have heard it originally came from slot car racing. In slot car racing they have some different parameters than in e-flight or other forms of non performance land or water based RC. The main thing is they want a hot running engine that will get a little more umph than the competition, without regards to longevity. The other thing is that most slot cars have very open motors that you can get the water out of easily.
Now to rubbing alcohol. This provides many of the same benefits as the water break-in, such as reduced motor temps, reduced to no pitting from arcing, but also adds a much better cleaning power for the commutator and the brush contacts. Alcohol also has a much higher vapor pressure, which basically means it evaporates faster and more completely than water, causing less corrosion. Alcohol is also flammable so caution needs to be taken that way, although I really doubt that anything would catch on fire with such low current and voltages.
The reason ice can be used is to keep the motor cool during break-in. Most of the time though, in my experience, if you run a motor at 1/3 it’s rated voltage with no load, it will probably not produce enough heat to really even notice, but if you run it at higher voltages it can be useful. If you would like to use this method just make sure to clean the water from the melted ice off of the motor, and out of the inside if any got in there. If you are concerned about motor temps, you can also break-in with your heat-sinks in place.
Alternately you can use a fan to cool off the motor. Try to prop up the motor so the metal isn’t resting on much (like a paper clip stand or a heat-sink or something) and put it in the air flow of the fan so in a way so that the most area you can is exposed to the moving air. This is usually an end on position to the fan, 90 degree’s to the air flow.
The Break-in Process
Basically what you want to do is take 2 new AA’s for 2 or 3s lipo’s, and 6 to 8 cell NiMH’s and NiCD’s, or 1 new AA for anything smaller. If you have two or more batteries, take them and tape them together so that the + button from one battery contacts the – plate of the other battery. Take two leads and solder them (or some other kind of electrical connection), one to each of the poles on the motors. Make sure the wires can handle the load of the motor. Most motors have a 1 ohm winding on the low end. This means on the high end they will take max 1A for every volt. So 2 AA’s would be 3A max, 1 AA would be 1.5 A max ect. Then test the leads by hooking them to the batteries. If you are picky, note which way the motor is spinning, and note which way it will spin in your RC. If they are the same go ahead and tape the leads. If they are different just swap the leads and then tape them. Let them run as long as you can wait (or until the batteries go dead), but an hour is probably the min recommended. You can also break your motors in with the heat-sinks on them if you would like them to run cooler.
One small note. If you are running small motors like the n20’s or the n30’s used on the tail rotors of 300 sized heli’s, if you run the AA’s till they are dead, it will take about 85 hours. So instead just run them for about 90 min.
If you want to break them in water or alcohol, just follow the above steps; then place only the motor in the liquid (keep the batteries or other power source out). When the hour is up, or the batteries are dead take the motor out of the liquid and blow out all of the liquid that you can on the inside, usually with compressed air, but don’t take the motor apart or otherwise the brushes likely wont seat the same way when you put it back together, and you’ll have to break it in again. Make sure to oil the motor back up. Only get the motor where the shaft touches the bushings or bearings, and use a light sewing machine type oil like 3 in 1. Don’t use WD-40 or anything similar because they are penetrating oils that are supposed to be used for loosening rusty bolts, and the oil just flips off at rpm’s, and can cause extra resistance by getting oil on the commutator (loss of performance). All-in-all these oils are really not made to lube.
The other option you can do is use a motor break-in device, such as the Intellepeak Ice. To do this you simply go to the motor break-in menu set the volts and the time. What I usually do is start out with low voltage and run that for a while and then step up until I get to the regular break-in voltage. Such as starting at 1.0v or 1.5v running for 30 min, then stepping up 0.5v and running another 30 min until I get to 3.0v. This is definitely on the more sure side, and might be overkill. Ultimately you pick how you break-in, or not break-in your motors =). One other note with the Ice, a lot of times the n30 sized motors do not draw enough current, so you will have to wire up another motor with a higher amp draw in parallel.
Note: After breaking-in, motors become more efficient, and overall draw less power for the amount of work they do compared to motors that don’t have the brushes seated. For example my n30 motors for the rear tail rotor drew 0.07 A when I first started breaking them in. After they were done breaking in they only drew 0.02A, and it’s the same situation with the main 370 motor on a 300 sized heli. No load before break-in they draw about 3 to 4 times the current as no load after break-in. This could also be a good way to tell if a motor has been broken in or not.
Thanks go to Choppersrule of RCU for the idea, and letting me use his picture of a break-in in ice, and also to SSG Scott of RCGroups for explaining different aspects of the heli, including motor break-in.
I hope not to ruffle any feathers by this guide if your practices or recommendations might be different. Instead this guide is meant to be one that explores all the options and lets the individual decide which one they want to choose. If you have any other options for breaking-in motors that I have not covered, let me know and I’ll try to include it. If you want to experiment with this method, you’ve got nothing to loose (except maybe a AA battery or two). If you don’t think that break-in is worth the time, you are also entitled to that opinion. This guide is just written for those who see a benefit to break-in and want to use it, but don’t know what the options are.
If you would like to refer to this info, please do not copy it in part or whole, but rather just refer to this link. I will also be making a PDF available with the same info with the help of SSG Scott. When I get that done I'll post that info, and I'll be glad to make it available for download (RCU doesn't seem to support pdf's, maybe they can host it for me somehow, or if not I'll have to do it by e-mail, or post it somewhere else).
Please feel free to PM me on RCU or RCgroups, username mrasmm
600k ohm Reading with Standard Rocky Mountain Hard Tap Water
Brushes After 90 min, Not Quite Seated
Brushes Before Break-in
Commutator with Splines
Commutator and Brushes
Dry Battery Break-in Arrangement (I got these clips from the local scientific store)
Ice Charger Break-in Settings With Parallel Wiring of Two Motors
Ice Method by Choppersrule
Motor Break-in Parallel Hookup
Water Break-in with Batteries, (Bubbles Note the Motor is Spinning)
6 motor break-in wired in parallel. Notice the small motors do not have 2 leads each, instead they have 2 negative connections to share between all the motors (the negative current passes through the motor casing, and they are held together by the internal magnets). I only had 10 clips and I wanted to break-in the 6 new motors I had. Also I used allen wrenches as power busses to transfer the power =P
For some reason RCU wont let me make pictures bigger than 800x600, so hopefully you can see what is going on... if not I'll have to get a place to host the higher res images.