For years the crank in most engines has been made by shaping the counter weight, threads, etc., boring the internal hole up close to the front end, and then milling a cross slot at the correct place and to the correct depth for the desired crankshaft timing. When I bought my first engine at about 10 my dad looked at it and said "that's a dumb way to build a crankshaft. Hardened all over. The sharp corners on the hole will cause fatigue, drilling the centerbore past the port will make it flex even more." He often wasn't tactful, but he was right about shaft design. The Enya 19 never ran enough to break but many other engines built that way did. Later on I bought some Super Tigres, both the C35 and the G-21. The C35 shaft port was milled with a round mill so there were no sharp corners, it also was 12.7mm(half inch) diameter. The shaft was copper plated except for the crank pin and the main, plain bearing which someone told me was to keep everything from getting hardened. I never broke one, and never heard of anyone breaking a C35 shaft. The G-21 was a different story. The shaft was bored past the port. The port had sharp edges, but the did use a mill will a radius on it so the port corners had some rounding. Even so, if you got a good G-21 and it started to run really well that would last a limited number of runs. Then the next flight it wouldn't set right and had trouble holding a setting. A couple flights later it would blow the front of the shaft out.
A Brat 28 had the same problem. A number of different versions of Fox combat engines had the same problem. Some were fixed by making the intake hole a bit smaller. Other people fixed the problem by using grinding or EDM machining to smooth out and open the inside hole.
It wasn't until the last 4-5 years I've seen a significant change. One friend, Al Ferraro, likes to do racing and also play with engines. About 4 years ago the Picco 051 came out as a dirt cheap car engine. He got several. They were quite fast, not quite up to Cyclon standards, but competitive. But the first on broke the shaft right across the port. On the others he filled in the front of the shaft with JB Weld epoxy(after a good cleaning), and shaped the epoxy to fair smoothly back into the shaft bore. He also rounded the sharp corners from cutting the shaft port. This simple mod made the motors faster and they lasted much longer and didn't break a shaft. All the F2D motors for the last 10 years have been doing this shaft fairing trick in various was for more performance.
Then a couple of years ago I noticed the Evo 36 was also fairing in the front of the shaft port by cutting the steel into a round corner and taking care to round the port corners. Last year I picked up an ASP 36, by the same company, and it also had the better shaft design. The port timing on these motors is very conservative so it looks like if you want to try some better motors for 80 mph or even Fast there might be something to be had here. The ASP 36 only weighs about 8 1/4 oz. set up for combat.
Topic: Shaft Designs (Read 1823 times)
