Author: Nathaniel Salzman

The Brudelli Leanster

Thanks to the Yahoo! tilting vehicles group, I just discovered the Brudelli Leanster. The front end geometry is functionally the same as the Aprilia Magnet and the Tilting Motor Works design. One thing it does differently is that it has a tilt limit mechanism that keeps the bike from leaning over too far. As the photos show, the bike is able to lean over full tilt and not fall over. That’s what I want for Project Streetliner. It’s very nice to see that it’s possible. I’m also encouraged by the structural details of the frame and suspension components. They seem to be the kind of things that would be straightforward to fabricate. Very cool.

For more, check out their website: Brudelitech.com

Donor bike

722904667_8ce5ea8949_o

So at some point in this process, I’m going to have to decide on a power plant forProject Streetliner. My plan is to purchase either a used scooter, or one or more wrecked scooters to scavenge for parts. The question is, which one? The thing is, as I’ve researched this project more in-depth, I’ve realized that there’s more to be had from the right donor bike than just the rear end. Part of this project is to minimize the amount of custom engineering I’d have to do. Whatever I wind up with, I also want to stick to that bike (or at least that brand) as much as possible so that I can minimize the number of spare parts sources I have to manage. In a lot of ways, this ceases to be a scratch vehicle, and becomes an elaborately custom scooter. I like the sound of that! Components should really include:

Brakes
Obviously the rear brake disk and caliper are already part of a scooter rear end, so that’s handy. But what could and really should also be harvested from a donor scooter are the front brake components (calipers, disks, wheels, lines) and both brake master cylinders as well. Ideally, I’d like to use a bike that has either two front wheels (such as the MP3) or dual disk front brakes on the single front wheel (such as the Aprilia Sportcity, or the Suzuki Burgman). That would ensure that the brakes are already balanced and matched to the wheels and that the master cylinder is already beefy enough. Some maxi scooters also include a parking brake, which would definitely come in handy on a 3-wheeler.

Wiring, switches, controls, telemetry
Harvesting the wiring harness, gauges, and other goodies out of the bike would save a ton of work. It’d be pretty dumb not to utilize the gauges, the hand controls, and other switches and such that have already been engineered to work together on the bike. Why wire up a custom circuit for turn indicators when there’s one already built into the donor bike?

Wheels and tires
There really isn’t much interchangeability to scooter wheels and tires. There’s not the aftermarket for rims and such like there is for cars. So I’m likely to be stuck with the wheels and tires native to that scooter. One exception I know of is the Piaggio QUASAR engine line that is shared between Piaggio, Vespa, and Aprilia bikes. The 12″ wheel of the Piaggio MP3 could be plausibly swapped for the 16″ wheels of the Aprilia. The main advantage there is that swapping to the larger size effectively makes the end gear ratio higher (and therefore adds to fuel efficiency).

So when it’s all said and done, the only parts of the donor bike I wouldn’t be utilizing are the front fork, lights, the handle bars themselves, the majority of the chassis structure, and the seat. That’s it! The last lingering question for me was engine size.

I’d originally envisioned this project to utilize a 250cc scooter engine such as what’s shared between the Vespa GTs 250, Piaggio MP3 250 and Aprilia SportCity 300i. That, or a similar 250cc engine from Honda, SYM, or Kymco. A 250cc motor is kind of the sweet spot between performance, weight and fuel economy in the scooter world. The MP3 seems an ideal choice for the obvious reason that it’s already a leaning trike. The MP3 also comes in 400cc and 500cc versions should the need to up-size arrive.

Speaking of which, I’m pretty sure at this point that up-sizing is inevitable. This is mostly because of the likely weight of Project Streetliner. My design criteria is to stay below 600 lbs curb weight. Scooters in the 250-650cc engine classes tend to weigh in between 340-550 lbs. Thing is, it’s not speed I’m concerned about, it’s economy. You see, a small engine having to work really hard will usually get worse fuel economy than a slightly larger engine that isn’t having to work so hard. (For example, on a racetrack a BMW M3 gets better fuel economy than a Toyota Prius when both are driven at the Toyota’s quickest speed.) So if my vehicle does indeed weigh 600 lbs, a 400cc engine will likely get better mileage (and conveniently give more power) than a 250cc.

So that brings me to my latest bit of hands-on research. I stopped by the local Suzuki dealership to look at a Burgman 400 — a bike considered by the folks who like such machines as the premier maxi scooter on the market. It seems perfect! The Burgman is the front runner right now for a couple key reasons. It already gets the mileage I’m shooting for, weighs in at 474 lbs, has dual front brakes, and a great reputation. Looking it over, it’s now the definite front runner in my search for a donor bike. What’s more, Suzuki has sold a boat load of them so there ought to be plenty around in the secondary market. That certainly can’t be said for the MP3, I’d wager. Anyboy have any other suggestions?

Full LEGO prototype

I love LEGO! The next best thing to working this out by hand with a big pile of LEGOs is using their software to render a mechanical prototype of Project Streetliner. Obviously, the proportions aren’t any kind of exact, but seeing the basic shape and structure in 3D has me pretty stoked. Also, having to work through the basic mechanical details (what stays solid, what’s allowed to pivot, etc.) has given me a much better understanding of the mechanics involved. All in all, it’s not that complicated. It’s also really interesting to start thinking about the structural considerations of the safety cage / chassis.

Now that I have this so much more planted in my mind, I’m actually tempted to skip the functional model all together and go straight for the Pathliner prototype. That’s probably not a great idea, but it’s a temptation all the same. I just want to keep moving — keep making progress.

LEGOs for prototyping

LEGOs are a great way to prototype something mechanical. But what if you don’t have enough of the right kind of LEGOs? Well that’s where the LEGO Digital Designer software comes in very handy. It’s basically CAD for block heads. Here I’ve rendered how my front end could work were it built out of LEGOs. I really think like I’m getting very close to where I can proceed to the next stage of prototyping: a functional small-scale model.

Fantastic correspondence from Bob from TMW

In the past few days I’ve had a terrific email exchange with Bob from Tilting Motor Works. His company has developed a fascinating kit to convert essentially any standard motorcycle into a leaning tadpole trike. But more importantly, he’s done over 10,000 miles of real world road testing on his tilting suspension design. I asked him if directly linking the shocks to each other had any adverse effect on handling. Specifically, I wondered if hitting bumps while leaning or in other tricky positions would give the vehicle any proclivity to change course suddenly or alter its tilt. This was his response:

Yes, the force can be transfered directly to the other wheel but my experience shows me that it is no issue even while cornering or going over railroad tracks.  Actually all suspensions ultimately transfer the force to the other wheels, just not as directly. I tested my suspension by laying 2×4’s all around my cul-de-sac and running over them at different speeds and angles.  The bike performed great.

This is such great news! A front suspension setup similar to what Bob’s developed seems the perfect match for Project Streetliner, but I didn’t know how capable that kind of dampening really was. I also asked Bob about comfort and he was happy to report that his front end is far more comfortable than stock and that his VMax prototype is always his first choice in a stable of fun vehicles. He’s graciously offered his time and expertise and I’ll be giving him a call very soon. Thanks, Bob!

Tilty wheel alternate

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!

Two for one

I had a fun realization yesterday. As part of my prototype roadmap, I plan to build a smaller version of Project Streetliner using bicycle components. This was originally intended to be a test platform just for steering/leaning geometry, suspension, and handling characteristics. I hadn’t even made up my mind as to whether or not to go to the full trouble of actually making it pedal powered. In general, I imagined that I’d just sort of slop something together as a proof of concept. But upon deeper consideration, I’m re-evaluating this prototype step for the better in two key ways. First, I’d gain a ton of valuable experience by going ahead and building a streamliner shell for that bicycle prototype. Not only would it be the place to perfect my fiberglass construction skills, it would force me to solve a lot of control linkage, entrance and exit issues, and other problems on a simpler vehicle before tackling the more complex road version. But what’s even more awesome than the learning value is that if I take the time to build this prototype to a good level of quality, I’ll actually have my very own tilting Velomobile — something that to my knowledge doesn’t exist in the marketplace right now. When all was said and done and Project Streetliner was on the road, I’d have two fantastic alternative vehicles. One perfect for commuting and errands on the open road, the other perfect for cruising the bike paths of the twin cities (and possibly being a perfectly viable commuting vehicle all its own depending on where I’m headed). That’s very exciting. I’ve even thought of a name: the Pathliner.

How to make a fiberglass mold

Here is an eight part series on the basics of molding and casting in fiberglass. I’ve done a lot of this before, but it’s very good to have a refresher. Casting key FG parts for Project Streetliner is going to be a major part of construction. I’m thinking that perhaps I need to go ahead and shell my bicycle prototype velomobile-style when the time comes. Although, that’s kind of awesome — if I take my time and do that prototype correctly, I’ll actually have two vehicles when this is all done. One for the highway, and another for the bike path. That has me thinking about electric assist…

Tilting Motor Works

I got an email a few days ago from Bob over at Tilting Motor Works. His tilting trike system is designed to be bolted onto the front of virtually any motorcycle. It appears to be using the same basic geometry as the German Tripendo recumbent bicycles and the Aprilia Magnet concept trike. His 10,000 miles of road testing seem to be a pretty sound endorsement for this kind of geometry. Good stuff. $10k is definitely beyond my budget for Project Streetliner, but I appreciate Bob reaching out and hope to still have him involved somehow.