Back again with another zany creation using air, all part of an overall theme of builds I call Fun with Air . This one, like my Rat rod turbine-styled dragster (RRTSD) , is also a RRTSD but smaller. My former dragster used the 75mm large diameter motorcycle wheels, and demonstrated how useful they can be in creating a turbine out of Lego. This project focused on the 62.3mm Porsche (42056) rims. To date, these rims have appeared exclusively to 42056. I am going to give the meat and potatoes first (pics and video), but a full explanation and details about the build is given below. I hope it is worth the read. Of special note although I spent a little time on looks, the main purpose of this build was initial speed, so, again, like most of my creations in the “Fun with Air” group I really wanted to keep the weight down. Therefore no special functions/etc. were added and panels and other elements for aesthetics were kept to a minimum. This creation was built out of 100% LEGO, and no parts were modified. The clutch mechanism that allows me to rev the engine and then snap the transmission in action originally appeared and is explained here .
Weight: 323 grams (77 grams turbine alone)
RPMs of turbine: Just over 10,000. See video. This was at about 60 psi. When I used higher psi, gears shattered when giving the car-a-go.
Length: 34 studs
Width: 13 studs
Final drivetrain gearing: 5:1 (3:1 x 1.667:1)
Comparison between old turbine (using 75 mm motorcycle rims) and new one:
The advantage or purpose of this project over my first RRTSD was first to test the properties of using the Porsche rim as a rotor versus the motorcycle rim. Because the motorcycle rim has a greater radius, it has certain benefits over other elements as a rotor. As a general rule, as we all know, the greater the radius of a rotating body the greater the inertial forces will be. However, the greater radius also means a larger, heavier build to house it in (not to mention, with equal air pressure applied, it will rotate slower). Although a heavy rotor can be advantageous for inertia with a large radius, the heavier body that is needed to house it in is not. The weight of both elements is pretty much the same, with the Porsche rim being slightly heavier (b/c it is so wide I suppose, 20 grams versus 17.7 grams). But because the radius of the MC tire is quite larger than the Porsche I think the MC rim has the advantage if one considers only the rim itself. Also, one has to consider that the MC rim has two more spokes than the Porsche rim (12 versus 10). More spokes/fins is advantageous in this context. But….. because the smaller Porsche rim allows me to save weight on the overall build (roughly half, 323 versus 717) I wondered if it might, overall, have the advantage. Also, the spokes on the Porsche rim are wider and able to capture more air. So there also are advantages there.
The results are not scientific nor objective. I tore apart my old RRTSD and therefore don’t have it for comparison. It would have been nice to race them against each other. But, I will say, the giddy-up in this build was at least comparable, if not exceeded, that of the old. In fact, if you see the video, there is some jumping and movin’ on some of the drag starts, similar to what you would see in a real dragster. I did buy a digital RPM counter and was able to count RPMs, and indeed, RPMs at 60 psi were just over 10,000. Pretty impressive. Any faster and gears were ripped apart. I still think that it is a testament to Lego’s durability that I can take an input moving at roughly 6,000 rpms (after gearing) and apply it to sedentary gears (rear axle) and have things remain intact. But any faster and they would not. I lost several 12 thin beveled gears in the process of this build. And stupidly, the LBG ones, not beige ones (much more common). Perhaps I should also make a video of that. It is kinda fun to watch.
Anyways, the project was a lot of fun. Served as a silly, but fun and educational project after long days at work. Hope you like it!
Quoting Angelo Filipelli
Very neat engine design. I once made a Technic V8 motor which somehow managed to go over 12,000 rpms. I secured it with beams and to this day I don't know how I managed to do it. Good work!
Clutch mechanism is here:
Nothing special, but like you point out, in my opinion it testifies of the strength of Lego. In fact, the clutch gears remain intact when other gears are shattered.
Quoting Jeremy McCreary
Fascinating project, NFP -- especially the turbine design trade-offs! Would love to see the clutch mechanism you're using. It's astounding that the drivetrain tolerates any of this.