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Rewinding HO Slot Car Armatures:

I was asked to create a document that would help others to be able to rewind their own armatures. Also to mention some of the things that work and some things that don't seem to work so well. I've been doing a lot of experiments on armatures mostly due to my own personal interest in figuring out what makes these things tick. Using my extensive professional electronics background as well as asking tons of questions of those in the know , and also having a personal mentor (which never hurts), I've had some pretty good results with rewinding. One piece of advice that I remember reading when I first started was that your first 6 armatures probably won't work so don't get discouraged. Best advice I've heard yet. My first 6 did work but barely. It takes a lot of practice but the final results are usually worth it.

As a disclaimer I don't claim to everything that there is to know about armature rewinding, theory, best winds, etc. I'm just willing to do the homework to figure it all out and then to share the results. Here goes:

Base for our rewind:
As a base I will be referring to the Tyco 440-X2 armatures. It is a simple conventional wind . Arms such as the Super G+ or Life Likes and others do some tricks with timing and alternate winds which just add unnecessary complexity to our task here.

Parts of the armature:
So that we are all on the same page? We need to speak the same lingo as far as armature parts are concerned.
1) Armature shaft : the rod assembly on which the arm (short for armature) is built.
2) Stacks:laminated segments with three poles (for our Tyco's) on which the wire is wound..
3) Commutator - the assembly at the front of the armature that contains : - plates on which the brushes make contact - tabs where the wire attaches to the com (short for commutator).
4) Wire- On stock Tyco's, its the red stuff.

Items needed:
1) Armature blanks - I've been using stock Tyco 440-X2 arms and unwinding them to get the blanks. Should only be about 2 or 3 bucks each. Don't get the epoxied ones. Hot stocks from some suppliers are epoxied and balanced. The epoxy makes it almost impossible to get the wire off. Stock Tyco 440-X2 arms are not epoxied and work just great for this.
2) Soldering Iron - I'm using a Weller 75 watt gun and a Weller 40 watt iron. You could get away with just one but I find both to be useful.
3) Solder - I'm using Radio Shack's solder (62% tin/36% lead/2%silver). 60/40 doesn't hold up to the heat.
4) Wire - I'm using the 1/2 lb. spools of 36 gauge P.N.(0858) (6000FT) and 34 gauge P.N.(0858)(4000 ft) magnet/motor wire from Belden. Improved heat handling on coatings of their magnet wire.
5) Ohm meter - one that goes into micro ohms. Else a simple ohm meter will be good enough to tell if the wires have a good connection on the com
6) Hemostats or very this needle nose pliers. Surgical tools help here.
7) Scissors - something like cuticle scissors works well.
8) Exacto knife - I like to use a number 11 blade.

Now on to the winding:
One of the best ways to learn how an armature is wound is to actually unwind one and watch how the wires are connected and how they unwind. Reverse engineering approach applies here. Since we have to get some blanks anyhow, this should be the first step. (Keep a second arm for intact for a reference).

Use an Exacto knife and carefully cut the wires from one of the com tabs. You will notice that one wire seems to be on top of one pole while the other is under another pole. Remember which way these go. Write down and draw how this looks as you go. We will reverse this process during the rewind.

If you are looking at the front end of the Tyco arm (com facing towards you and pole w/cut wire at the top) the wire that seems to be on top unwinds to your left. Unwind this one first. You can count the number of turns if you'd like or I can save you the time. 180 turns per pole on Tyco, 172 on Super G+. One way to quicken this process is to just hang the arm by the wire and let it unravel.

Also notice that the com tab is directly centered between the gaps of the poles of the stacks. This is a neutral timing (No advance or retard of the timing). For the stock Tyco arms, the com has a couple of dove tails on the back that will interlock with the stacks to set the com to a neutral timing. So go ahead and cut the rest of the wires from the tabs and slide the com off of the arm and get it out of the way. Unwind the rest of the poles.

You should now have a blank armature. Now place the com back on the arm. If you forgot which end, the longest side gets the com. If you aren't sure, use the reference arm that you should have and compare the ends with it. If you put the com on the wrong end, the pinion gear will be too far back in the chassis thus won't meet the crown gear correctly.

Next we need to lift the com tabs very slightly to accommodate the new wire. I use a number 11 Exacto knife and just slightly cut into the front of the tab where the wire goes on so that I can get enough bite to gently lift the front of the tab. These are soldered but just a little pressure will break the solder and lift the tab. Be careful here. Don't want to break off the tabs. Do all three tabs. Use a pair of cuticle scissors to remove any remaining wire from around the tabs.

Now its time for the wire:
I suggest 35 or 36 gauge for starters. I use the 75 watt Weller to tin a spot on the wire where it will go around the tab. Add some solder to the tip, hold it against the wire for a while (30 seconds or more) until the insulation has burned away and the wire has been tinned. Belden claims you need about 750 to 800 degrees F to break through the coating which is why I use the 75 watt gun for this. Clean the tip of the iron often to keep the impurities out of the solder. Coating material gets mixed with the solder during tinning. I use a pair of hemostats to guide the wire under one of the tabs. Place the wire under the tab and wrap it out over the top of the tab. Make sure the tinned area is under the tab. Use your hemostats and gently squeeze the tab down to hold the wire in place. Don't solder it yet since the very last wire is going to need to go under this one too. Now remember what you wrote down earlier? OK just in case you didn't, you will want to start your wind (with com side of arm facing you) by taking the wire around the far right side of the pole to your right. Lay it down flat and take it all the way around that pole. You should remember from taking the wire off how it went around the same pole for 180 turns. If using 35 or 36 gauge wire, do 100 turns. You want to lay the wire down very flat and tight. Not too much pressure to where you will break the wire but you want it tight. Also make sure that the wires are laying down parallel to each other. You don't want to have wires crossing over the flat winds. Causes unwanted technojargon to occur. Keep the wires up against each other in a parallel fashion until you get to the end of the stack where the wire wants to and must wrap over itself. Then reverse the direction of the layers to go the other way but still keeping flat and parallel. You will do this until you have achieved the desired number of turns. In our case 100.

Now there are two schools of thought on how to tie in to the next com tab. One is to cut the wire that you just wound, tin it, place it on the next com tab and start with a new tinned wire from there for the next wind. Another is to do a continuous wind. I vote for the continuous wind. Find where the wire will lay over the next tab, remember that spot, unwind one wind and tin the wire at that spot. Don't tin too wide of an area though. We don't want it to short against the stack or any other wires. Rewind the last turn back on the pole and place the tinned wire under the next tab. Squeeze it down and repeat the process that you just did on the first pole, on the next pole. And then again for the last pole.

Now when you get to the end of the last wind, very carefully lift the first tab that you did, tin the end of the last wire and place it under the tab, press the tab down, clip off the extra wire from the last wind and its time to solder.

Soldering the tabs:
Before you continue, remember: YOU DON'T WANT TOO MUCH HEAT ON THE COM!

Some choose not to solder the tab but instead to let the tinned wire and the tab pressure do the work. I prefer soldering the tabs. I believe that it gets more amps to the winds thus the arm performs better. Using the weller 40 watt iron, I place a little solder on the tip of the iron and then touch the iron to the tab of the com.


Got your attention? Good. This is critical. Too much heat and the com plates will separate from the mounts thus rendering the arm as junk thus wasting all that hard work.

Place the iron on the tab, count for 3 seconds and get off the tab. Even is its not done yet. Move to the next tab and do the to 3 seconds. Round robin approach. Let the com cool down and then start again until you have good solder joints on all tabs. You want the solder to get under the tabs a little and on the wire as it enters and exits from the tabs. Not too much solder though. Just enough to make the connection. Too much may rub against the inside of the front bulkhead causing all kinds of uglies to occur. Takes careful soldering and some practice. How do you know when the solder joint is good? This is where the ohm meter comes in. Meter between two of the com plates. Start with any two. Then meter the next two plates and then the last two. All three resistance readings should be approximately the same. The closer the better. For example if the reading from the first two plates happened to be 2 ohms. The next two readings should also about 2 ohms. But lets say that you had sets of plates two at 4 ohms, and one set at 6 ohms? Do the solder again to get better connections. They should be very close. If these readings are very different, the arm isn't going to run very well.

There are a few different reasons for gluing your work.

One is to keep the wire from unraveling. Epoxy works well here. I've also had good luck with Super Glue (liquid not gel). I've tried some without glue and depending on how full the stack is, you may not need to glue these at all. Fuller stacks such as 36 gauge /120 turns per pole or 34 gauge /100 turns per pole, should probably be glued. Also the wires do actually move around a little and expand and contract and all those things that cause the coating to eventually wear off. Gluing limits this action as well thus adding some longevity to your arms life span.

Another reason to glue is to assist in dissipating the heat from the arm by filling in the air pockets between the wires. One way to do this is to place the arm in the oven at 225 for about 20 minutes, mix some epoxy and place that in the oven for the last 5 minutes with the arms but in a separate pan and then soak the epoxy into the winds. Another way is to soak the winds with Super Glue and let the arm dry overnight. Super Glue seems to work just fine with this scale arms. 1/24th arms probably get a little too hot for the super glue but the ho stuff works out just fine with it. I've actually had a test arm, that I was putting through some heat tolerance tests, that the solder let go at the com but the wire was still intact around the poles. I re soldered the com and the arm still ran. I've also read some information that claimed that super glue burns around the same temperature that the solder actually melts. The main reason that I use the super glue instead of epoxy is for reusability of the arm if it should fry. The wire can be removed easier than with the epoxy. Important for experimenting or you would go through a ton of new arms in a hurry.

While we are on gluing: The Tyco 440-X2's com tabs are held in place by a plastic retaining ring. The ring is directly in front of the tabs where the wires attach to the com. Higher revving arms can cause this ring to separate from the com thus causing the tab plates to separate. Not a good situation during an important race. Place a little Super Glue directly in or on the seam. Not on or between the com plates. Another fix is to coat a piece of thread with epoxy and then wrap it directly around the front of the ring to keep it from moving. I find the super glue approach to work very well with less mess.

While we are on tips: Another problem area with these arms is at the rear of the arm just behind the stacks where the winds can touch the metal arm shaft. The arm shaft can get pretty hot thus eventually burning through the wires which can cause a short thus causing the arm to fail. To fix this get some heat shrink tubing that will just fit over the shaft (about 1/16th of an inch diameter). Cut off a short piece so that it doesn't interfere with the rear bulkhead later. Slide it over the shaft and up against the stacks. Glue if you want but not necessary. Now wind the arm. The tube acts as a heat shield. During my experiments this was a major problem area. I haven't had a problem since I've done this fix. I've noticed that some of the much older arms actually had these. Newer arms don't.

There are some very good articles that refer to balancing the arm using precision tools or a set of razor blades etc. I use the razor blades and they seem to work just fine. This is where the epoxy works best. Place the arm across a set of evenly placed razor blades and carefully (Don't get cut!) roll the arm. If it seems to stop in the same place, put a little epoxy on top somewhere like between the stacks in the gap area and roll again. Do this until the arm is balanced to your satisfaction. Set arm aside to let glue dry and your off.

Truing the com?
A jewelers lathe seems to be the recommendation here. I don't have one yet. Since I'm just experimenting with these and not producing them professionally, I can get away with a little trick here. Get some sanding film and a drill press. Just like truing up tires, true up the com. I'm not recommending this for professional use. If you are going to run in a big race, send the arm out for service. If you are just tinkering, this actually works surprisingly well. I've brought back some old arms and coms from the dead this way. The sanding film starts somewhere around 2400 grit and goes finer from there. It takes very little off the com.

OK we now have a custom rewound arm. Now what? Now we need to put this arm in a setup. For the above arm, 36/100, that you just wound, motor magnets are critical. Too weak of a magnet results in a burnt arm or melted com or even a melted bulkhead. Too strong, top end suffers. For the above arm 36/100, I have been using poly phase III magnets . Phase IIs will work for shorter races and smoothes out the handling a little. Phase IIIs have a little more torque and the arm runs a little cooler. I've watched 36/95s smoke using Phase IIs for long races. Also make sure that the setup is as loose as possible. Not binding parts such as gears or stuck axils, rubbing wheels, etc. or you will increase heat and shorten the life of the arm. The whole drive train matters.

Electrical systems also make a difference. Got to feed the amps to the arms to get the performance out of them. Adjustable silver electrical systems work great for these. Copper will work but the difference is definitely worth going to silver. I've tried gold contact shoes but the silver seems to last a little longer and perform great. I didn't notice any performance gain by going to gold and the shoes wore out quicker for some reason? For the adjustable brushes, don't torque the brushes down too tight. Just enough to reduce the blue arcing at the com. Don't want the brushes to be cutting grooves into the com plates.

7 tooth pinion and 24 or 25 tooth crown for most cases. You want to keep the arm cool. Doing something drastic such as 8/20s could result in a meltdown if races lasts over 3 minutes.

For some lighter winds such as super stock levels, you could go to something like 7/23 or 7/22 go with as small a tire as you can run without actually dragging the traction magnets around. Then again, some like to drag these around on the tycos. Experiment.

Now for some stuff that's a little on the advanced side: After you've accomplished the above, you may want to try some different things.

Timing is a fun area to play. For racing you would probably always want to advance the timing. That is turn the com so that the com tabs are ahead of the poles in the direction that the arm is rotating. I like to advance the com to the left or counterclockwise (with the com facing you) as opposed to the right or clockwise which I believe is standard Tyco rotation. Haven't had any stock setups for so long I'm not 100% sure. I do counterclockwise. What this means is after you have your arm with its timing advanced, you want the arm to rotate in the direction that you moved the com from the neutral position. If you advanced the tab counterclockwise, when the arm is running it should spin in that direction. Else it would act as a retarded timing? Tow truck arm? Tons of torque but very little top end.

A timing tool or create one of your own by rigging up something with a protractor, is required to know what the timing setting actually is. Guessing doesn't buy you anything here. You should set the timing before you do the rewind. You are already familiar by now with the little dove tails behind the com that forces the com to a neutral timing. Using your exacto knife, cut those off. Now the com will rotate freely on the arm. Using your timing tool, set your timing, add a little super glue to where the com touches the stacks to lock the com on the arm and your are ready to wind again. I recommend no more than about 25 degrees advanced. I like it around 20 to 22. Going too low results in less top end, going too high ends up in burnt arms. I've tested 0,+5,+10,+15,+20,+25,+30,+49 on same winds. Yup, did them all and +20 to +22 has a very good full power curve. + 49 actually ran. Not too well but it did run. + 30 was weak on the low end. Experiment and you decide. Learn by doing.

Different winds:
I've tried many types of conventional and a few non-conventional winds of many configurations. There is an unlimited world to explore here. So explore it.

Some suggestions on winds that may help get you going: Some of my experiments included 36 gauge wire at turns per pole of 90,95,100,120. 105 through 115 seem to be more midrange. Going below 90 has a little too weak of a power curve for my liking.

I've also done some experiments with 34 gauge wire at turns per pole of 75,85,90 and 100. 100 is a little tough to get on these arms but it is possible and runs pretty well. Must glue the wire down though or it will find a way to unravel. Going too low to say 60 runs too weak to make it worth my while to make any more of these.

Double winds?
Very powerful but don't live quite as long as the singles. Do the same way that you do conventional winds except you are now winding two wires at once. A little more tricky to keep flat. Takes practice. If you want to go against theory and some of the pros advice, do the double winds as layers. Wind the first wire for targeted number of turns and then wind the second wire. Some say it won't help. My experiments have proven that on narrow gap arms like these tycos, it actually creates more torque and better acceleration and a much fuller power curve. Seems like the stack covers the wire and smoothes out the magnetic field a bit. Parallel winds of the same configuration won't even get close to touching the layered ones if both are done on these type arms. Now on the wide gap arms this is a different story. These won't behave the same. Too much torque to control. That's why I believe that the narrow gap stacks that cover more the winds makes the difference here. Its all a matter of what you can get away with for the sake of power. Also try removing or adding segments to the stacks. Makes a big difference for torque and top end. Some numbers to try: 36 gauge at 60 turns double wound. This is two wires at 60 turns each per pole. Give this about a 20 degree advance and give it some phase III motor magnets. Also do one of these as a layered wind. Super on torque and yet very controllable. Make sure these are wound on the narrow gap arms. Try this with only 50 turns. Try a triple wind 36 gauge at 30 turns per wire per pole. Check the rules before running these in an organized race. May not be legal? But they are still fun.

Keep in mind that there are many aspects that can alter the behavior of an armature such as the timing, stack length, stack gap (wide, narrow...), strength of magnets, spacing of magnets, gauge of wire, number of turns per pole or the length of wire approach, types of winds, balancing, truing the com,gear ratios including the tire size, friction in setups and the list goes on. Experiment. Have fun. That's what its all about isn't it?

I'm open to discussing anything above with anyone that wants to know or has advice to offer. Yup I take advice too. I'm the Mad Scientist and you can contact me at stemmlers@usa.

Mad Scientist

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