A recreation of Lotusís ďbig boyĒ Elise with motorized brakes, 4-speed transmission, 2 x RC Buggy motor drive, and much more.
About this creation
Photos are found at bottom of post
Car at a glance
Propulsion: 2 x RC Buggy motors Steering: Front wheel, 1 x RC unitís steering output Drive Type: RWD Transmission: Synchronized 4-speed dual-sequential with 1 x M motor Brakes: Directly onto wheel with 1 x M motor Weight: 1.763 kg (3.886 lbs) Length: 43.5 cm (17.1 in, 54.5 studs) Width: 19.2 cm (7.6 in, 24 studs) Height: 10.4 cm (4.1 in, 13 studs) Power source: 7.2v Eneloop Ni-Mh via RC unit Estimated part count: 2500 pieces Suspension: Full dual-wishbone independent Opening doors V6 piston engine Opening engine hatch and doors Build time: 95 (!) days
This vehicle is my first in three months, due to the difficultly of recreating the original vehicleís aesthetics. My recreation features 2 RC Race Buggy motors for the drive system, a 4-speed dual-sequential synchronized transmission , motorized functional brakes, full independent suspension, and a V6 engine just as in the real vehicle.
Introduction and Original
Itís been a long time. For me, that is; I usually post every 1-2 months and this time itís been 3. The reason for that is actually a mix of my own foolishness and incompetence (meaning my mistake of choosing this car to model), but I still hope that the end product has been worth every bit of the wait. Anyway, I hereby present my newest supercar: the Lotus Elise S Club Racer.
The Elise S Club Racer is a heavy modification of Lotusís already quite capable Elise S. Weighing in at just over 844 kg (1861 lbs) and providing 217 bhp (220 hp), is offers a formidable power-to-weight ratio in a relatively modest package; that is to say, it costs half as much as a low-end Ferrari and gets twice the fuel economy. Not bad. The engine is a turbocharged, mid-mounted V6, which drives the rear wheels through a 5+R manual (or automatic, your choice) transmission.
In building this car I was looking for a balance of performance and accuracy; a LEGO Technic supercar is fun, but you have to be able to drive it as well. To this end it was equipped with several advanced features, all of which I will go over in the following description.
I recently managed to acquire 2 LEGO RC Buggy motors and the whole accompanying RC assembly for a very cheap price. For those of you readers who have utilized this system before, you know what that means. For those of you that havenít, let me quickly describe the RC Buggy motors. They are power-hungry, extremely powerful bundles of RC fun. None of LEGOís other motors even come close - the Buggy motors each provide over twice the power of a PF XL -, and it seems somewhat surprising that the LEGO Group hasnít released an improved PF version.
Naturally, I turned to these motors for this vehicleís drive system: hard-coupling them at a 2:1 gear reduction before feeding them through the transmission. The transmission was a modification of this transmission here , made smaller and with slightly modified ratios. The functioning of it was still identical, and I will post instructions for the transmission soon. The transmission is my smallest 4-speed yet, and to my knowledge it is also the smallest 4-speed sequential LEGO transmission on the internet. Instructions for the transmission coming soon.
After the transmission, the drive was fed into the differential before being distributed to the rear wheels. A major challenge was making a narrow-enough driven dual-wishbone suspension; conventional driven LEGO dual-wishbone suspensions are 25 studs wide and I needed mine to be 23. This involved discarding the gearbox part in favor of a custom complex assembly. I suppose that Iíll post instructions for that, too. A replica V6
piston engine was connected to the drive system.
Steering and Brakes
Steering on this car would have been simple if not for the rear brakes system.
Let me explain. The LEGO RC unit comes in two variants: one has an auxiliary port and one doesnít. This car utilizes the version with the auxiliary port, which still wasnít enough for this car as the transmission motor used up the auxiliary port. My solution? I connected the brakes motor to the auxiliary port, but with a Power Functions switch in the middle, connected to the steering system. This ensured that the brakes motor would only activate when the car was turning left. This method actually worked perfectly, and I believe that it is a viable method to be used in the future.
The brakes system itself was as simple as it possibly could have been. It consisted of two rubber LEGO parts, each of which would press onto one of the wheels. Because of the law of the lever and the diameter of the wheels, the brakes system proved quite effective stopping the car - or holding the car in place while on a downwards ramp, as I tested.
The aesthetics on this vehicle were a huge challenge, particularly the headlights and the side airvent shown above. In selecting a car to build, I (meaning myself and my younger brother/building partner) was looking for two things: large wheels (so I could still get away with the 68.8 x 36 ZR wheels in a small package) and uniqueness. I didnít want to make a car that had been done 20 times before, and so the Elise was a good choice. Itís not a very exotic car, so why hasnít it been done often before?
The aesthetics are the reason. Thereís hardly a straight line to be found on this car, every section of the vehicle being covered with 3-dimensional curves. Not an easy car to recreate with blocky LEGO bricks. Flexible hoses were a huge help here, as were LEGOís selection of curved and angled plates. Even so, I will be the first to admit that the aesthetics are not quite perfect, despite the 2 months of build time they consumed.
This car was built in the hopes of performance, but it unfortunately turned out too heavy and large to attain a high speed. My next vehicle will reiterate the same mechanical concepts in a lighter package. Overall the car functioned quite well, and the transmission is a considerable improvement over the previous version. The car was also an effective demonstration of why some cars receive more attention in LEGO form than others: the curvier the car, the less LEGO versions one will find.
Man, this car is pure awesomeness all day !!!! Looks brilliant and I like the way you mixed
in some bricks to get a better finishing design. Gearbox works fantastically well and I love
the fact that rear wheels breaks for cornering....outstanding job in every way ;)
Yes, you are right that the stalled torque of the PF XL is higher, but not by a factor of 5: http://www.philohome.com/motors/motorcomp.htm. Also, it may depend on which motor output you utilize with the Buggy motor. The Buggy motor's sheer power (4.61 W as opposed to the XL's 2.21 W) is usually enough to account for the torque-lacking power curve. The transmission in this vehicle helps with that, but is not always neccessary, as shown here:
According to Philo's motor page, the XL has ~5 times the stalled torque of the RC Race Buggy motor, and our experience bears that out. Torque decreases linearly with motor shaft speed from there. It's hard to make up for that much of a torque difference with gearing and still get a decent top speed out of an MOC.
Thank you! You are right, the RC Buggy motors do have less torque than PF Ls and XLs - but it's really not by much; a RC motor will output 5.7 ncm of torque as opposed to an L motor's 6.48 ncm. I think the primary flaws with the RC motor lie rather in its extremely power-hungry nature, and its tendency to overheat. Gearing is a problem that can be fixed externally.
Excellent sculpting, engineering, and write-up! You ran up against the fundamental problem with the RC Race Buggy motor -- peak mechanical power is high but often inaccessible for lack of torque. (Ultimately, torque is what overcomes opposing forces like gravity, friction, and water resistance, not power.) In powerboats and heavy vehicles, we get much better speed and acceleration from optimally geared Ls and XLs.