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Figure 25: M o d d in g the b ru sh holder. File d o w n (sh a d e d area) until only 1/64 in. rem ains below bru sh hole. Check that the brush will easily slide through the brush holder, otherwise deburr the edges with a square file. With the complete bullet plates on, check for alignment by sticking in a piece of 3/32 in square tubing through the whole assembly. Variations on a theme: if you wish, skip filing down the brush holder and instead cut a slot in the plate so that the unmodified brush holder can protrude down into the Vee. Solder as before. To have even more efficient heat dissipation, your bullet proofing plates can be done 'elephant ear' size, sticking out a good bit from the endbell. This is dependent on how much space you have in the chassis. It won't look pretty, but it's efficient. A rather primitive form we invented about a year before 'real' bullet proofing became the vogue, was to solder a piece of braid to clip and brush holder. This piece is allowed to stick out a good bit and will dissipate heat surprisingly efficiently. Concerning the bearing, use either a Mura or a Champion bearing, according to the endbell make. A Mabuchi bearing will quickly develop an oval hole, so I cannot recommend it. Bullet proofing the bearing is frequently done. Either remove the outside edges around the bearing hole screw on the plate and apply a few quick dabs of solder, or reverse the bearing and solder it to the plate from the outside. See photos. As with the case bearing, polishing the inner surface to a high gloss is advisable. Bullet proofing the bearing is usually only done on can drive' motors. ★ ★ ★ ★ 21 brushes & springs With that, we have completed the requirements for the first two items, bearing and heat proofing. Remains securing the current conduction. On a stock endbell. the current will go via the spring and via contact between brush and brush holder. The latter is rather erratic when the brush is vibrating during running, and the increased current through the spring will heat it up and make it lose pressure. What to use here is shunted brushes, meaning that the current will go directly from lead wire joint via the shunt to the brush. Shunted 22
Bulletproofing, elephant ear size. These are made from silver-painted plastic, just to show you how it can look. Just about any shape is acceptable, as long as It won’t short-circuit via the chassis. Holes (should be many and small) are drilled for lightness and quicker cooling The first bullet proofings simply consisted of soldering a piece of braid to the clip and brush holder. Even today this trick could be used to further increase heat dissipation on a bulleted endbell. brushes can be bought ready-made, both Champion and Titan are good ones. Using these, just tuck in the shunt ‘tail' and solder. Otherwise, shunting your own brushes is easily done. Got some flexible lead wire and strip off the plastic sleeve insulation. Insert the brush and jam the shunt wire between brush and spring. See photo. Then just solder the other end of the shunt wire directly to the lead wire clip. Simple, wasn't it? NOTE: try sanding the brush slightly where the shunt wire will lie against it. Careful . . . that carbon is brittle. NOTE, lately, using double shunt wires to each brush is becoming popular. Another trick is to insulate the spring with a piece of plastic sleeve on it (not the brush end of the spring). NOTE: unless your black Mura case will turn pink from this, I can recommend good ol' Mabuchi brushes. Correctly shunted, they are superb. Pay attention to the springs, and make sure you use strong ones. Champion's are my favourites. If you are looking for really strong springs, I can recommend those from Model Racing Car Centre. Warning, though, as they will eat the brushes in a very short time. As for springs, shape them like in figure 26 and make sure they have an arc of at least 120 degrees NOTE: springs and brushes should be changed between every race, to keep performance up. Some people will even change springs A very good job can be done with square tube for brush holder and home-made clip. Champion's bullet plates are instead given a Vee to fit an unmodded brush holder. Unfortunately, these will only fit Champion's own endbells as standard. With a little modding of, say, a Mura endbell, though, they can be used. The usual way of bulleting a bearing. Bearing it knocked out, turned around and soldered in the plate. This will allow the bearing to run cooler - high temps can cause a ’break-down' of oil or grease. Don’t forget to polish the inside surface. 23
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