I'm genuinely surprised that it lasted as long as it did in all fairness. I thought it'd fail far before it got any temperature in it. Very interesting!
it is interesting to notice that the rod handled pretty well the static and dynamic loads generated by the piston movement, despite the fact that it failed because of the friction at the bearing points
it's be interesting to see how long it would last with a metal bushing in the ends, something like phosphor bronze, instead of the petg because it looks like it failed because of friction at that point
Miniature modeling engines are a great hobby, almost like Formula One technology. The motors are subjected to heavy loads and the test selection of appropriate technology elements, etc. There should also be openings or slits to replace the oil, as in the case of the original crankshaft, and for longer work it would probably form the connecting rod element under the influence of a higher temperature. In miniature high-speed motors, however, connections with a colored matte are more durable in the long run.
@@Fuaarrkk there are multiple types of plastic that are multiple times stronger than steel. It's very doable theoretically, not using a 3d printer but certainly maunfacturable
He should have used the bronze bearings. Even the aluminum rods have them because they can't handle the friction. I doubt that the heat radiated of the piston will be enough to melt the con rod right away. You have to consider that the fuel-oil-air mixture is also cooling the moving parts (because of evaporation).
Stuart Smith In this case, friction was the reason why the con rod failed. I don't think it would have reached the 80 degree celcius that fast. You can see in the video that the heat damage accures on the bearing surfaces.
You'd actually be surprised how many cheap weed whacker engines are using plastic conrods now! I used to do an engine lab for students were we broke down such an engine to show the parts, and, sure enough, it had a black plastic conrod!
What was wrong, with the 3.3's connecting rod? I played with 3.3 Revos, for over three years and no failures. Proper breakin and they were as good, as anything else. I had 4 3.3's in various cars (Tmax, Revo and 2 Jato's). Not a single one failed and i wasn't easy on them, From local racing to speed bashing they worked fine. I play with brushless now, much less cleanup, but have 0 bad memories of 3.3 connecting rods. The 2.5 was s different story, though is was tuning, not failures in that case
@crazyjr they have a channel in the middle of the connecting rod that creates a weak spot and it will split in half from bushing to bushing. i've never done it, but i always get them in for repair like that.
As a concept if worked, but you always knew it would fail fast. However, you proved it can be done. Tech moves on, next time this could work. In other applications it may be necessary for a fail to happen at a timing or load. Nice job.
cool video. expected a little more destruction but the plastic held together well. That engine is awesome and i like how just about every part is replaceable.
i have a feeling the weirdly 'modified' or mangled crank pin (the pin where the connecting rod attaches to) has a lot to do with how the rod failed (after the fail: the bend in the rod, the shape of the hole, the crack or scorch or whatever on the side of the rod) the top hole(piston side) is probably totally fine. but we never got to see that part lol
Next time you should make a brass bushing, for the ends of the Rod. I believe it was excessive friction, that caused the failure. You can see the way it moved (the plastic), inside the lower hole. I'm not saying it wouldn't fail anyways, but might last longer with the bushings
I really do like what you do. You are a talented machinist. Also I saw that you are obviously into rc stuff. You should make a video about your planes. I would really like to see them.
I think you should add a metal bushing onto it, like have it impregnated into the plastic so it doesnt move. Looks to me like the friction melted the bearing surface which caused the rod to twist and deform further up. Idk could have just been the camera angle when the part was shown at the end
Put some copper or bronze bushings in there, even the stock metal connecting rod has bushings pressed in. Nothing is going to survive metal on metal like that without a bushing.
Hey Johnny! Long time fan! If you are interested, I could print this connecting rod out of nylon for you to test, if that is something you are unable to print. I'd be willing to ship it to you at my cost as well, just to see it tested!
Not sure if anyone's mentioned it yet or not, but the big end of the conrods all have small oil holes in them. If I missed the part where you drilled one, my apologies, but if you try it again with a small 1/32" hole, you might get better results.
You should have done that garage 55 way instead of making a plastic connecting rod make the Piston itself plastic it probably wouldn't work for a long but it would be super cool!
Exactly what I expected. But there was no hole for lubrication in that plastic connecting rod, so of course it´s melting. But I think it would melt also with a lubrication hole, but maybe one or two minutes later.
It may not have failed , if you had drilled the lubrication ports and put bushings in the rod or even better a bearing ..on both the wrist pin and crackshaft connecting points ..how ever I think the plastic used for a 3d printer are engineered to get soft at a certain temperature.. it's probably possible to manufacture a connecting for out of a piece of a Teflon kitchen cutting board ..as Teflon is rated for higher temperatures .. plus just the general properties would make Teflon less likely to create as much friction , I had a buddy make a piston ,rod and sleeve in his dad's ceramic shop , whitch actually worked out better then he expected , I believe he still uses that engine today in one of his plane models ..
could I suggest you consider using the 3d printed conrod and do a last wax type of casting in aluminium by building a gas forge would also open up a new world of projects for you
I highly doubt it, but it would be cool. If they can make the parts as strong as the aluminium ones and the manufacturing process is faster, then there are some chances.
nice vid Johnny! Since you are the best with the lathe, I would like you to introduce brushless motors to your channel (high KV motors to be exactly), Could you make a big gear with 5 brushless motor around connected in parallel to convert 50k rpm to 5k rpm? those motors are really powerful but not really efficient at 50k rpm and would be a great idea to move a large prop or to use it on a go-kart or e bike, there are plenty of 3750 KV motors on internet and they are powerful and cheap! but a big brushless motor is really expensive !
That leaves the question was it thermal expansion because the friction or just the surface of metal to plastic without enough Lube that caused the failure? 1+ trying brass bushings.
lolatmyage the idea is to experiment with the longevity of the part made from that material. Those tiny cheapo tire inflation pumps use plastic rods, so why not try an RC motor? Hand crafting that tiny dog bone would be much harder, and probably not much faster than printing one
It lasted longer than I thought. Might of done better with carbon fibre filled nylon or peek. But the cost of them is far to high. Still cool experiment. Great video. Keep up the good work.
Would it have worked better with the brass bushings fitted in the con rod holes? Like you had on the metal one? The brass might reduce the friction heating of the plastic moving on metal at such high speeds. Also what plastic filament did you use? Some of the low temperature plastics like PLA would get soft with that level of friction. Nylon might be a good choice.
