This submitted to Tumblr by lamidesign:
I wonder if there could be a more mechanically simple solution than tilting the wheels. The wheel tilt is all about moving the CG – the contact patch is the same, and the tires really don’t care if they vertical or tilting.
Can the entire sprung chassis pivot, or rock – I’m thinking like the inverse of a hammock between front and rear supports. If the body of the car leans into the turn then the wheels do not really have to.
That’s a good thought. I had to think about this for a moment and based on my research, here’s what I’ve concluded.
You are correct about contact patch — the tires won’t care one way or the other and shifting the CG is indeed what adds to the dynamic stability of the vehicle. But there’s one key reason why the front wheels need to tilt with the body: conservation of angular momentum. Utilizing the physics already induced by the spinning wheels to lean them over (and the body with them) is already the simplest in terms of mechanism (even if it’s a little harder to wrap your head around). I can let the tilt mechanism free float and lean the vehicle just with the steering inputs — like I would on a motorcycle (via counter-steering). If I keep those wheels straight up and fixed but want to lean the body, I’d have to use a powered mechanism to force the body to lean into the turn. Were it just a hammock, like you’ve described, the natural inclination of the body would actually be to move the CG to the outside of the turn (because of inertia) which would quickly flip the trike.
The same gyroscopic force that holds a two-wheeler up is also the force that allows you to lean that vehicle via counter-steering. If I were to use a delta trike (two wheels in the back) instead of a tadpole trike, then I could use the angular momentum of the steerable front wheel to enter and exit the lean like you would on a motorcycle — all while leaving the rear wheels fixed (there are a number of bicycles that work this way). Unfortunately though, on a vehicle the size and weight of Project Streetliner, I’m afraid that the single wheel might not actually provide enough leaning force unless it were a pretty massive wheel. Furthermore, the complexity of driving two rear wheels instead of just one becomes just way more trouble than it’s worth.
In 1983, Mother Earth News built a three wheeled leaning vehicle called the 3VG. It used hydraulics to lean the body of the vehicle into the turns. They seem to have incorrectly assumed that a 3-wheeler could not tilt on counter-steering alone:
Although we tried a number of different mechanisms in our efforts to find a system to induce camber in the car (because it has more than two wheels, it can’t lean naturally like a motorcycle), only a handful proved successful. The “inclination” is at present controlled through a combination of mechanical, hydraulic, and electronic components … all of which are available as “off the shelf” equipment, and some of which are so basic that they’re commonly used in many toys and pocket calculators.
Both the Piaggio MP3 and the Tilting Motor Works prototypes prove that natural leaning in a tadpole trike works just like it does for a conventional 2-wheeler. They later describe the supposed problem of the force it would take to lean a vehicle of the size of their prototype:
It’d be ideal, for example, if the lean system were a stone-simple mechanical affair with a minimum of moving parts, but research showed us that such a design has some real drawbacks . . . one of which is that it takes almost superhuman force to initially lift the vehicle from the full-bank position. That’s why we use hydraulics.
As I read that again, it sounds like they were again operating under the assumption that tilting the front wheels and using counter-steering simply wouldn’t work. They don’t really say if they ever actually tried. It sounds like they were trying to lean the body independent of the wheels, which would certainly require amazing force to overcome the weight and inertia of the vehicle body — especially one as large as what they built. Given what I’ve seen from both the MP3 and the TMW bike, I think that the size and weight of the vehicle could indeed have a significant impact on its ability to utilize counter-steering. I can only conjecture that the Mother Earth News boys either never tried, or that the significantly larger size and weight of their vehicle was more than the angular momentum of the wheels could easily overcome.
My design spec is to keep the vehicle weight under 600 lbs. The Piaggio MP3 500 weighs in at 530 lbs, so if I’m able to land anywhere in that weight range, then I should be just fine. That does bring home the point, however, why this vehicle isn’t going to be something that anyone could just get in and drive. If you’re not already a competent scooter or motorcycle rider, the coordination necessary to pilot a vehicle such as this would be completely lost on you, as you’re essentially turning the “wheel” right in order to go left. That’s hardly intuitive, even though we’ve all done it on bicycles since we were kids. That’s also why it won’t have a steering wheel at all. Ha!
Thanks so much for your submission!