Suspension concerns

I have a couple of concerns about this suspension geometry.

I understand it, and see how everything connects and moves, but my concern is about the rebound and dampening. The wheels are obviously able to move up and down as well as tilt on the a-arms, but with the shocks hooked to each other it would seem like the suspension travel of one side is dependent on the other side being planted. This is disconcerting. The last thing you need on a leaning vehicle is wonky suspension. Sure this arrangement tilts just fine, but what happens when you’re deep in a lean and run over a pothole? Does the vehicle shoot one direction or another? It’s enough of an issue in traditional 2-wheel vehicles. So this is something I’ve got to get figured out during the prototyping process.

My prototype roadmap is as follows: Final concept » small-scale component prototyping » small-scale radio controlled, fully-functional prototype built mostly from R/C car components » large-scale prototype built from bicycle components and driven either by pedal power, electrics, or moped engine » full-scale chassis prototype with full drivetrain » polished full-scale vehicle made from chassis prototype and finalized.

Last night I swung by R/C Car Kings, a descriptively named shop in Burnsville, MN just up the road from my apartment. They’ve got every R/C car component known to man or beast in there. Fantastic stuff. I’m only just starting to understand the ins and outs of automotive suspension and as I’ve said before, I really want to engineer as few components for this vehicle as possible. Thankfully John, their resident suspension engineer, was on hand to walk me through my options. He expressed the same concerns I have about the pivoting, linked suspension on the design I’ve been referencing. He walked me through the different types of car suspensions and suggested either a king-pin set up (similar to what the Piaggio MP3 uses) or even a trailing springer suspension. Both are a tad tricky as they require me to essentially hang the entire front suspension (in terms of dampening and rebound travel) on the steering knuckles along with the brake calipers and wheels. It’s not impossible, it’s just complex. Anybody have any insights?

Suspension insights

Here we have a clear CAD rendering of the leaning front suspension in what appears to be an early version of the Aprilia Magnet concept. The one thing I couldn’t figure out 100% in looking at previous photos and video was just what exactly the struts attached to. It seemed clear that they attach to each other, but I knew there was a pivot in there somewhere. Looks pretty simple now that I can see all the components. Can’t wait to model this. I’m really curious how I’m going to source the upper and lower ball joints and spindle assembly. Might require some custom machining in the end. Hope not. The less of that I have to do the better.

The Tripendo

The Tripendo tilting recumbent trike is a big influence on my design thinking. Its wheels are set much wider than the Piaggio MP3, which should allow for a more substantial cabin, but seems to limit lean angle. Either way, I imagine that a bicycle-class prototype of my vehicle will likely have a lot in common with the Tripendo. What I have yet to figure out is exactly how the suspension pivots work. I’m going to have to build the geometry in scale before I’ll fully understand it, I bet. I’ve based my sketch template on the seat height and ground clearance of the Tripendo, while stretching the chassis and shrinking wheel sizes from 26″ to 19″ overall (allowing for a standard 14″ maxi-scooter wheel)


The Mercedes-Benz F 300 Life-Jet

Via Gizmag, this Mercedes Benz concept vehicle is trying a little too hard to be a car. Such an odd thing to come out of MB. As neither a cabin motorcycle nor a proper car, the balance point is pretty unappealing in my opinion. Perhaps I’m self-referencing too much, but it seems like the kind of person who’d be interested in a 3 wheeler is either looking for fun, style, or crazy economy. This doesn’t seem to offer any of those. Very interesting to see how they approach the front suspension and rear swing arm, however. I also wonder if the lean is computer controlled. That’s always my suspicion when I see a traditional steering wheel in one of these vehicles. Something tells me they’re not counter-steering.