Book 3

More documents

Recommendations

Info

Mini-Wheels' epoxy, which will stay together during racing - at least we have never had this epoxy crack in our tests. (In a 24-hour, for example, we ran an arm that was epoxied half with Araldite and half with Mini-Wheels. The Araldite cracked.) If you cannot find this epoxy in Britain. I suggest sending for it from some American mailorder firm. The Mini-Wheels stuff is a 24-hour epoxy, but by heating we can make it both cure quicker and flow out more evenly. Therefore, place a small amount of mixed-out epoxy and your armature in close vicinity to your hot solder iron. Use a piece of wood - not balsa - with a shallow 5/64 in. hole in it to have the arm stand upright. Heat for 15 minutes or so, especially the arm should be thoroughly hot. Then grab the armature shaft in a pair of no-knurl pliers and apply a thin coat of epoxy with the help of a match or a toothpick. No great slabs are needed, just a thin coat that will flow out and impregnate the wire. Smear a little on the com tying thread, just enough to cover it. but leave the solder joints free! Too much epoxy is dangerous, it will act as a dead weight and a heat trap, with consequent less performance and more heat. I assure you that very small amounts are needed - see photos. I am no fan of put-it-in-the-oven school, instead I recommend that you place the armature near your hot solder iron where you can easily keep a check on it all the time. The hot epoxy must not flow out on the shaft or into the com segment slots. However, if you only have put on that small amount of epoxy, it will usually stay in place while curing. But check often, and turn the armature upside down every two minutes or so for the first half hour. Then you can shut off the solder iron and let it cool slowly while keeping the arm nearby. Changes in temperature should be performed slowly - the trick of directly taking the arm from oven to refrigerator can cause dangerous temp stresses on epoxy and insulation Now the epoxy should be rather stiff, so put the arm away and let it cure the rest overnight. Of course, should the need arise (like working all night trying to meet the sign-up deadline at 8.30 a.m.). you can always keep on heating the arm with the iron. I have once prepared, wound and balanced an arm in 5 1/2hours, but I would rather not do it again, even though I managed to win that race. NOTE: do not forget to check that the com sits in the position you want. Finally, getting the epoxy to cure and then discovering that the com is all wrong, as I have seen happen, is not very funny ... for yourself. it it it it 16
Ways of balancing. The worst method is this one (top), from a Champ 507. with long slashes ground in the pole surface. The Dyna method, filing up notches (next down). The best method of removing weight, drilling holes in the pole surface (bottom). The arm here turned out fairly well balanced after winding, so only two small holes were needed Now for balancing, with the method that at least 99% of the readers m ust be familiar with - the Razor Blade Method. Check that edges of blades really are parallel. Heating the lead epoxy on the arm. Shift between placing the arm with the lead epoxy top and bottom, so that it will not flow out too much. 18 balancing (static) Now the armature is wound and epoxied. but we are not out of the woods yet: it has to be balanced first. Why balance? Well, when doing the armature, we have usually not quite managed to get the wire and the epoxy on evenly, with the result that the armature will be heavier on one side. Only once in my nine years as a racer have I seen an arm that turned out perfectly balanced (static), but unfortunately, it was not mine. Anyway, you can see that happens very seldom, so chances are your armature will need a little work. If we put our unbalanced arm in a motor and have it run. centrifugal forces will try to force the heavy side away from the shaft, causing vibrations, friction and heat. Friction and heat have already been discussed in general and it should be obvious that these are bad for performance, but let us consider vibrations. Vibrations - any vibrations - in a car are detrimental, since they will spread everywhere in the frame. And you can easily imagine what kind of roadholding you will have with the rear axle trying to jump up and down . . . (You should watch worn gears, bent axles and out-of-round wheels, too, since these can cause serious vibrations. Ideally, gears and wheels should also be balanced for maximum performance.) So it is clear that the armature should be balanced, and the obvious way is to either remove weight from the heavy side or add weight to the light side. For static balancing (we will discuss dynamic in a moment), the tried and true method is to place the armature on a pair of razor blades stuck into a piece of balsa. Blade edges must be parallel and horizontal. When the arm is placed on the blades, it will turn until it 17
Page 1: Model Cars Bok3 MOTOR TUNING the co
Page 4 and 5: s e lf flu xin g w ire FOR ALL M O
Page 6 and 7: Now the brilliant range of Hi-Speed
Page 8 and 9: R ig h t, w hich arm h a s been sim
Page 10 and 11: Left to right. W rap the wire end a
Page 12 and 13: Left to right. A close-up of what t
Page 14 and 15: 16 pointers Stripping: making a goo
Page 18 and 19: ests with its heavy side down. Note
Page 20 and 21: I mentioned that after winding and
Page 22 and 23: Figure 25: M o d d in g the b ru sh
Page 24 and 25: The other end of the shunt wire sol
Page 26 and 27: these if necessary. If you have acc
Page 28 and 29: Tell your friends about Model Cars
Page 30 and 31: ai WANT: | slot car 'bits'. fast ma
Page 32: Prlmod by Graphic Art Services (Bri

Book 3

Create successful ePaper yourself

Delete template?

Save as template?