Back again with another creation. Perhaps even zanier than my last creation using air, but part of an overall theme of builds I call Fun With Air . This one is an air-turbine powered rat rod dragster. Try to say that five times fast! 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 more time on looks, the main purpose of this build was initial speed, so, again, like my last creation I really wanted to keep the weight down. Therefore no special functions/etc. were added and panels and other elements for aesthetics were kept at a minimum. This creation was built out of 100% LEGO, and no parts were modified.
Weight: 717 grams (260 grams turbine alone)
RPMs of turbine: 8-10,000 (est. – see below for details)
Length: 45 studs
Width: 15 studs
Final drivetrain gearing: 15:1 (9:1 x 1.667:1)
The main feature of this build is that it is driven by an air turbine engine. Building air turbine engines out of Lego has a very short, limited history. Youtube documents some turbines built out of Lego but findings are sparse. Those that were done were more like in 2009-2011ish and not much else has been done since. In addition, they were bulky, color-vomity, and limited in functioning.
The turbine created for this build was designed to at least appear like a real turbine engine. Gearing is internal and is geared to roughly 9:1. The turbine is also fairly modular, can easily be taken apart by separating the two halves of which comprise it, and gears easily changed. Gearing to 9:1 (internally within the turbine) produced the best results for the drag racer but I also changed the gears and experimented with 2.8:1. This ratio did not work well at all and involved too many breaks in the drivetrain. 9:1 produced no breaks, slips, etc. In the main video above you can see it working, internals, etc.
Building was a little more tricky than it might appear at first glance. But I have to say, I am happy with the geometry of it all. In my opinion connectors are much underutilized for structure/chassis builds. They can be quite strong when combined with others. As can been seen in these pictures, the rotor was a Technic motorcycle wheel. This piece offered many advantages. It is very robust and therefore the rotors would not bend/move to the pressure of the air. It is also pretty beefy. Once it got moving the inertia of the rotation kept it cookin’ for quite some time. The geometry added up perfectly to the encircling #4 connectors. Although the wheel got very close to the edges, as can be seen below and the video they never actually touch the sides of the turbine.
The cross section shot above shows the internal gearing. Although the axles did not fully penetrate to the other side on the final model they did on the initial model. I tried to make the turbine as compact as possible without creating too much friction so I tried it as such (usually you want axles to penetrate to the other side for greater strength. Widening the turbine and adding liftarms between the gears below would have allowed for that). So in the final model I shortened the turbine and the space for the gearing (disallowing room for the axles to penetrate to the other side) and it worked just fine. I did give the half-bush space on both sides of the gears so they would not be flush against the liftarms and connectors (too much friction).
I made the car a little customizable. Initially I didn’t think I would really add any looks, but as I got playing with things, well…. it just became more and more fun. One version is your classic rough, edgy, rat-rod look, complete with rat-faced gear shifter knob. The other is a more hip, night-out-on-the-town, pimped-out look.
The drivetrain is the same to my pneumatic dragster . Interested parties can look there for reference/information. Overall, I must state that I am impressed with the LEGO clutch gear, drive ring, and changeover catch. In my previous project using this mechanism we saw that using the LEGO gears, drive ring and catch held when trying to engage gears moving at an estimated 900 RPMs versus 0 RPMS (1500 RPM x 0.6 = 900) and the elements did just fine. Here, we see them engaging an estimated 1100 RPMs versus 0 (10,000 RPM x .11) and the elements also did just fine. In fact, when I stated earlier that I used different gear combinations in the turbine, the other being 2.8:1, that would mean I am engaging a gear moving at an estimated (10,000 RPMs x .36) 3600 RPMs with one that is not moving at all, and guess what, the LEGO elements discussed above worked just fine! I did not keep the arraignment because, like I said, it failed but this was NOT because of discussed elements. This is because it ripped apart the internal gears in the turbine or other parts of the drivetrain. But the catch, drive ring, and clutch gear all remained intact.
NOTE: The estimation of 10,000 RPMs is just that. An estimation. I don’t have a speed counter and did not buy one for the project. Maybe I should have. I did some research and other similar projects and saw a range of 8,000 to more than 30,000 RPMs. Given that I was using much heavier turbine blades mine is likely moving at the lower end of that range. But, given the sound of the turbine heard in the videos, and when holding the turbine while it is going and feeling the gyrations, I feel that 10,000 is likely an accurate estimation. And yes, I did use lubricant. I took the motor apart initially after the first set of videos and saw no damage. I need to take it apart again and inspect for damage a second time. I used 60 PSI of air pressure to drive the engine in the engine-only demonstration in the video; 90 PSI of pressure when actually driving the vehicle. The last two trials in the video did not even use the neutral setting. As can be seen, as 90 PSI the car runs just fine with the gears engaged from the get-go.
Quoting jds 7777
Awesome! Have you seen the Lego turbine tractor pullers on youtube?
Yea, as I mentioned the history of such engines is there..... it is just dated and pretty much non-existent in the last few years. I think it can be very fun. There are several things I wish for a revival. Pneumatic engines are one. These turbine engines are the other.