Thiemies LegoLego AutoLulu S LegoLogan S LegoLuke LegosNicks LegosLego CamperLego EvergreenLego PicksForwardHave always loved LEGO, how about this little camper RV thing?... they always…I'm quite an amateur at this - there are some awesome builders out there, for example Sheepo and Sariel, who are FAR more competent at LEGO vehicle design than I am. That said, I'm happy to share the factors that came to mind."Fastest" comes down to top-end speed at the end of a drag race, as a starting point. Basically, the car's being run as a dragster - in a straight line. There are four factors I see for accomplishing this:-> minimizing drive train friction-> maximizing onboard power -> weight distribution-> smooth upshiftingAnywhere any of the LEGO elements comprising the drive train touches other elements, there will be friction. Careful alignment can help, but a good design that minimizes friction, touch-points, and intermediate gearing ("idler" gears) is better.Some designs have technic "snaps" holding rotating gears in place as part of the power train.
Even if they're not "full friction" snaps (that are a bit hard to rotate), there is going to be a good amount of friction building up heat there, and heat buildup can deform the snap, and make the friction worse. The faster you go, the worse this problem gets.The left part of this LEGO pin element is a "snap", and the right part is an "axle": It's tempting to use these to keep intermediate gears in place - find another way! the above element can definitely slow down a LEGO drive train. Better to use an axle with a stop instead: ...here's an example - right at the end of building this awesome transmission, this guy introduces friction - skip to 12:12 or so to see what I mean:There's no rule that a LEGO vehicle has to be powered by only one battery. There's also no rule that power to the wheels can't be additive - combining the outputs of more than one running motor. With a good additive gearing design, you can end up with some pretty insane resulting power to the axles - easily enough to start melting plastic at the friction points, get wheels to accidentally go flying off of their axles, etc.
So be careful - LEGO at full speed can be quite dangerous.: Batteries and Battery packsLEGO batteries come in various sizes and shapes, with differing voltage and power levels as well. The rechargeable Technic battery in the center of the above picture even has a variable output power level feature!Above chart courtesy Sariel. His Downloads page is chock full of wonderful information about gearing, motors, drive trains, suspension designs, steering designs, tutorials, and more.There's a LOT of info available about each kind of LEGO technic motor, and each kind of LEGO battery. Choose and use whichever LEGO motor has the best power-to-weight ratio and choose and use whichever LEGO batteries have the best power-to-weight ratio for your needs as well.Dragsters are shaped like they are for a reason. Most of the weight of the vehicle gets applied downward on the rear wheels during heavy acceleration- the front end's light as a feather, and dances in the air, practically, as the car accelerates down the track.
I'm not going to get all Math-y on you, but this picture certainly will:...(image courtesy Andrew Dressel via Wikipedia)Work toward ensuring the weight's in the back of your design, if you want a car that accelerates well. If the CoG is too far forward, it stops helping keep the rear wheels on the ground, and starts being a "dead weight" on top of the front axle, every ounce of which works against the goal of zooming down the track. Oops, I used an abbreviation... CoG = Center of GravityWhether integral, or remote-controlled, unless your vehicle has a CVT like this: ...it's going to have a gearbox, and you'll need to get it to upshift as part of getting to full speed. So... figure it out - CVT? Each solution has its advantages and disadvantages. Transmissions are some of the biggest challenges, design and implementation wise, for LEGO vehicles. Even with some experience under my belt, I have no clear answers for you on this, other than "experiment, and find what works for you".
What if I'm not building a dragster?What if your LEGO vehicle's not intended to go fast in a straight line? What if it's intended to be a fast RALLY car? I made an assumption at the start, and we've been focused on straight-line acceleration yielding the eventual speed that'll result in "fastest". It's possible you're looking at it from another angle - maybe the perspective of building model rally racers - fast RC LEGO cars that can corner well, turn on a dime, maybe even drift through turns... :-) There's a bit more to worry about in the case of a rally car, not only because "steering" but because physics.-> ensuring the CoG is low enough for good cornering-> precision of steering implementation -> precision of implementation of "return to center"-> smooth downshiftingensuring the CoG is low enough for good corneringBasically this comes down to putting batteries and motors down so their CoG is near or below axle-level. It's hard to get things down that low - but it's worth it, if you're intending the vehicle to survive turns at speed without toppling over on its side.precision of steering implementation Many LEGO cars end up doing "hard lefts" and "hard rights" well, but can't change lane position smoothly.
Gear chatter and backlash start to play major roles in steering designs. Rack and pinion is a great idea, but a challenge to implement well.precision of implementation of "return to center"When driving a real car, you turn a bit, then let go, and the car's steering returns to driving the car straight ahead. LEGO based steering solutions that include return-to-center have a big advantage over those that don't.Rally driving involves slowing before turns, and emerging from a turn in just the right gear. If your vehicle has a multi-speed transmission, the design will almost certainly favor upshifting smoothly over downshifting smoothly, or vice-versa. Eliminating gear backlash is almost impossible in LEGO - so... how will you balance things? I've struggled with LEGO transmissions for years... maybe a CVT like the one from Sheepo that I've highlighted in the video above, really is the best solution. Some designers implement BRAKES separately, and have RC braking as well as RC acceleration and RC steering on their vehicles.
ONE LAST FACTOR - the FUN factor.I think, with LEGO more than with almost any other medium, it's important to remember to have fun with it. It's easy to get frustrated when you're not "making progress", and it's easy to start thinking about things like using superglue, non-lego-components, non-lego-batteries, etc. Do it the LEGO way - play well.I have well over a half-dozen half finished LEGO projects sitting around. They don't drive me - I drive them. If I feel like contributing some to one of them or another, I do it. There's no deadline, no project plan, no promises to be kept - only fun to be had.I guess what I'm saying is, rather than blasting away at building the very fastest LEGO car ever, I recommend for you instead to take time and enjoy some number of months or years of exploration along this path.Take the slow road, and enjoy the experience. OR... maybe take the fastest possible route! If you're impatient, you can buy a ready-to-roll "TOY"-OEM'd RC LEGO car, from last century's LEGO RACERS line.
Maybe this might be just what you need? I love the ones I have. They're sort of cheating, but since some of the models are/were actually LEGO-branded products, sort of not cheating at the same time. They don't replace "100% LEGO" designs, but they sure are fun.They're basically easy-to-use RC cars with LEGO-sized holes on them, so the bodies can be modified however you desire. the cars undercarriage is one large part, with almost everything: RC unit and antenna, battery compartment, motors, steering. the wheels are removable, but not interchangeable with other LEGO wheels.While you can no longer buy these directly from LEGO, there are good deals around for used ones. Also, the manufacturer, "TOY" in China, is still making and selling them today, but without the LEGO branding. A quick google for "toy brand self assembly rc car" helped me learn that they're now branded "SDL". Suppliers, Manufacturers, Exporters & ImportersI've had a lot of fun using these RC cars as "bases" for LEGO builds.