3D accurate renderings
So as things keep moving forward on the proportions and details of this design, I've noticed that my three-quarter renderings aren't as accurate to the profile views I've been working from. I am not a CAD pilot. I don't have the right software or the right experience to model this in 3D for real yet. That'll probably happen before I'm done, but what I did want to see is what this design might look like from different angles. So what I did was take some advice from Twitter and pull my profile views into Google SketchUp. Now while Greg (on twitter) was suggesting I model the whole thing in SketchUp, it won't give me the kind of results I want for the sheer amount of time I have to put into it. All I wanted was better perspective renderings I could use in Illustrator. This was this was the result:
What I think is particularly interesting is just how much the forced perspective changes the visual relationship between the wheelbase and the width of the body. In the front view, you can see just how far apart the wheels are, but in the other views, they look like they're right on the body. It's also interesting how it looks really mean from some angles, and just a tad messerschmitt from others.
Entry/exit cutlines and mechanism
People have been asking how getting in/out of the Streetliner is going to work, so I've rendered what that might look like. In concept, the canopy (when attached) will hinge along the right-hand side of the vehicle, and a car-style door will open on the left-hand side of the vehicle. (I've also added a lip to the wheel pants to kick the wind off the surface of the wheel just a bit. I really like the look of this detail as well.)
Thoughts on the canopy
While discussing the Streetliner with my collaborators at work, the subject of the canopy came up. That sparked an idea for me. Rather than having to form (or pay to have formed) a singular canopy, it'd be a lot simpler to build the canopy in sections. Each of those sections would be much smaller and much easier to make. I think I could pretty easily create forms and heat-bend polycarbonate panels for the windows and windshield. In fact, in this configuration, a glass windshield might even be viable if it weren't too expensive to get fabricated. But beyond ease, having a roof on the canopy would mean the cabin would be cooler. It's also that much meaner looking. I like that too.
Concept finalization
I'm gaining more and more momentum when it comes to finalizing the Streetliner concept. I'll be putting together a more comprehensive full spec post later, but for now, here's an update on the exterior design. I feel like I've finally found the art deco mojo I've been looking for all along. While the updates are subtle from concept Echo, a lot has gone on under the skin to help me arrive at this, the most finalized shape to date.
Most significantly, I realized that my seat and human analog were actually too large, as was my representation of the ATV drivetrain — each by about 20%. This meant that I could shrink the wheelbase as well as the cabin size by significant amounts. I had previously been concerned about the front to back balance of a rear-engine design, but these new proportions make it seem like it won't really be an issue.
I accounted for a "jack shaft" that will inevitably be required to get proper rear wheel sprocket alignment. It also allows me to more easily monkey with the final gear ratio to the rear wheel. Additionally, it allows for easy fitment of a belt-drive, which will require much less maintenance than a conventional chain. I reworked the rear suspension in such a way that I can still get a lot of travel, but I don't have to build a whole subframe back just to intersect the shocks. I've essentially just extended the rear swing arm. What may not be obvious from the side rendering is that there are arcs involved that would allow the shock(s) to be centerline instead of at either side of the swing arm. In the rendering there's a ghosted wheel showing the full 6" suspension travel. The jack shaft is inline with the pivot for the rear swing arm, which should keep things nice and smooth.
Front and rear, I've simplified a few things, and added others. Most noteworthy is the addition of a rear window, which is something I hadn't had in the concept previously. The view won't be great, but it'll be much better than nothing. I'm thinking that rather than a rear view mirror, I'll utilize a rear-facing camera built into the high brake light assembly. That will have a better view than any mirror system that would conceivably work (although I did have a hilarious rear-view periscope idea). I also abandoned previous modern-style brake lights and turn signals in favor of more conventional round lights. This is actually more in line with the classic design language from cars in the eras I'm trying to emulate. In the end, I'll be somewhat limited in what I can find off the shelf, but standard round light will actually look better, in my opinion. I was designing those other signals and lights almost in a vacuum. I think they were cool looking, but in the end, such modern details would look out of place in this shape, I think.
Lastly, I finally paid some real attention to the front cross-section of the vehicle. I was able to resolve the shape such that I now have a completely flat front suspension parallelogram, but still enough body and wheel clearance to get about 40º of tilt out of the vehicle before the wheels bind or the body touches the pavement. I know for a fact that I've never put 40º of lean on any two wheeler I've ever owned, so this ought to be plenty. What's more the cabin ought to be pretty comfortable, with little compromise toward comfort. It should just fit me, but with some reasonable room for comfort.
So let's hear it. What does everybody think? If you've got other ideas, now is the time for them. As far as I'm concerned this is the design I'm moving forward with. I'll hopefully be starting a small scale foam shape prototype today and I'll share progress as soon as there is any. I'll also be doing some small-scale safety cage models, likely in brass tubing, for structural testing and evaluation by people who know more about this crap than I do.
Safety cell construction: looking for your thoughts
I'm getting to a point of critical mass with this project. I'm feeling like it's truly time to "shit, or get off the pot" as they say. While I have no doubts as to my desire to truly see this project happen, I've been distracted of late and have a few lingering things I need to figure out. So I'm throwing those topics out for discussion to keep them moving forward.
Firstly, I need to finalize the broad chassis design when it comes to the safety cell. One of my major design criteria for this vehicle is that the driver be completely protected, much like a race car. Obviously weight is a consideration, but every bit of stiffness gained from driver compartment reinforcement is also stiffness gained for better handling. I feel very finalized in my plans to have front and rear sub frame assemblies that hold the front suspension and engine respectively. These would be tube steel and would bolt onto the safety cell in some manner of catastrophic break-away fashion, regardless of the safety cell's construction. The question then remains of simply which method of safety cell construction to adopt. Here's what I'm considering:
Steel tube roll cage — This would be similar to a rock crawler, drag racer, or any number of purpose-built oval track race cars like dirt track or even NASCAR vehicles.
Pros:
- Relatively lightweight at approximately 100-150 lbs.
- Very sturdy.
- Lots of known quantities and standards from organizations like the NHRA.
- Relatively easy to construct and customize.
- Reasonably inexpensive.
- Provides structure for the chassis as well as protection for the driver.
- Very easy to just weld things onto it or cut things off of it.
- The thickness of the safety cell could be less than 2" , which would help keep everything low-profile.
Cons:
- Very rigid geometry in terms of shape. Complex curves are really hard.
- Requires some extra equipment (welding rig and pipe bender).
- Not as lightweight as some alternatives.
- Provides only stiffness — no energy dispersion.
- Would need to be jig built in order to prevent heat warping.
- Would have to create separate inner cockpit lining and separate outer body shell that would attach inside and outside of the cage.
Composite safety "tub" — This is the kind of safety cell used by may alternative vehicles like the Aptera and is based on F1, Indy, and even high speed race boat designs. It's also comparable to many of the structural construction techniques used in making high performance small aircraft.
Pros:
- Very lightweight and rigid.
- Can be made in any shape.
- Inner surface can be the cockpit lining and even be contoured to make up the seat.
- Outer surface can literally be the body shell, so no body attachment necessary and weight/complexity savings in unifying the body with the structure.
- Can be constructed with simple tools for shaping foam and then laying the FB or CF cloth.
- In an impact situation, the layers of composites and foam would not only provide protective rigidity but would actually absorb a lot of energy.
Cons:
- Fewer known quantities in terms of rigidity and real-world safety (although that information is probably available through F1 and other sanctioning bodies).
- Could be more difficult to adjust it on the fly if a big change was needed after it was made.
- Need to do a cost analysis, but it might be slightly more expensive (only because steel is actually pretty cheap). Not sure how much that much foam and FG and resin will cost.
- Will be thicker (possibly 4"-6" inches thick), which could create clearance issues during lean and general bulk
Aluminum and fiberglass monocoque — This is an idea I had yesterday after a brief visit to the EAA Airventure Museum. The idea would be to utilize flat, machined aluminum bulkheads and ribs that interlock at right angles to each other. Then I'd fill the gaps with foam and fiberglass a skin inside and out. Put another way, it's the F1-style safety cell, but instead of just being solid foam, it's got aluminum bulkheads and bracing throughout.
Pros:
- Stiffer than the all-composite cell, but likely still lighter than the steel tubing cage.
- Inner structure would add a lot of stiffness, probably surpassing either of the other two designs
- Flat bulkhead designs mean that all the truly structural components could just be water-jet cut and then put together like a kit. It'd be self-aligning and could just be MIG welded at the joints with an aluminum-core wire.
- It would provide solid metal anchor points for things like the seat, harness, and the subframes front and rear.
Cons:
- Heavier than the all-composite cell
- CNC work required to do it right. It wouldn't be something I could make correctly myself. That means expense both in programming and machine time.
- Might simply be overkill, although over-engineering the safety cell isn't really a bad thing, now is it?
My favorite option at the moment is the third concept. Perhaps just because it's the newest idea, but there does seem to be a lot of elegance to the interlocking aluminum bulkheads. I'm looking for input. Give me your thoughts. What have I overlooked? Is there a structural engineer in the house?
Design concept Echo
It's little more than doodles at this point, but this is Concept Echo for the Streetliner. Of all the concepts I've rendered 'till now, this one is easily the closest to what I've seen in my head in terms of its sensibility. It's got some wonderful '30s and '40s era automotive cues, but also some modern flair. Most of all, the rear end is really feeling the streamliner locomotive, art deco vibe I've wanted to always have present in this vehicle. The next step, I think, will be to render it in floral foam, then shell and paint a mockup. I'll be doing this at a much larger scale than before, set off of 4" wheels and built onto a sort of mockup under-chassis that should let me fit a number of test body shapes moving forward. Think of it as the small scale prototype for shape and aesthetics, rather than mechanicals (that's a separate, ongoing thing all its own). 
Introducing contributor Nate Erickson
A few weeks back, Nate Erickson — colleague and crazy talented industrial designer at the product development firm where I work — kindly volunteered to do some Streetliner sketches for me. His love for cars and his professional abilities mean that Nate has an ability to think in shape that I can't even approach. What I was hoping for, and what he's constantly delivering, was that he'd bring some fresh aesthetic thinking to the Streetliner project. This sketch is one of many groovy renderings he's done lately.
New 3/4 rear renderings
I've never really rendered the Streetliner from this angle, but I'm loving the way it looks from behind. No tail lights or turn indicators, obviously, but the shape is very pleasing. This is based on the ATV drivetrain I've been thinking through lately.
More ATV thinking
So the seed planted by Aaron to use ATV drivetrain is growing into something cool. On twitter, @blalor suggested Honda's line of TRX sport ATVs. They're 2WD, chain-driven, EFI, and possibly perfect. I keep eyeing the 400 and 700 models. Both are single-cylinder "thumper" motors with a wide bore and thereby tons of available low-end torque — which will come in handy once I gear it up. I wish Honda were more forthcoming with horsepower numbers, but I'm not finding any. That's but a detail at this point though.
This ATV setup lets me do a couple things. It lets me run a larger motorcycle wheel and tire on the rear. That gives me higher gearing than both the scooter drivetrain and the original ATV setup by default. Rear sprockets are very easy to change, and this gives me lots of latitude in adjusting the final gear ratio of the drivetrain without touching the actual transmission. Reading up on the TRX specifically, there are aftermarket solutions for high performance exhausts and apparently it's pretty straightforward to re-map the EFI. That should let me tune a "butter zone" where the motor is at it's most powerful in its high ranges and it's most efficient in its low ranges. That way under acceleration, I've got plenty of power, but while cruising, it should just bump over and sip fuel. What could be even sweeter is if I could set up a switcher box of some sort that would let me pick between two EFI maps on the fly. One for power, the other for efficiency.
One thing I was very curious about was how the chassis would need to change in order to incorporate a separate engine and rear swing arm. One of the simple beauties of using a scooter drivetrain is that the engine, transmission and rear suspension are all basically one big piece. This is simple, but it isn't automatically light and there's no reverse gear option. So what happens when I swap out for an ATV/motorcycle rear end?
I found some reference images of the TRX700xx powerplant and rendered up a quick cross-section. This image compares the original concept Suzuki Bergman powerplant with the TRX. Everything is approximate, of course. The other key shift in this rendering is that I dropped the seat height basically to the floor. This to decrease the forward cross-section that much more. The trade-off is adding about 10" to the wheelbase between the two changes. This puts the length at about 3" longer than the wheelbase of BMW 3-series coupe. Not bad, considering it'll present about 1/3rd the frontal area.
The next question was obviously what does this do to the body shape? Making the hood line lower and the tail longer did some neat things for the side shape of the body. I especially like how that big wheel looks in the rear. The overall effect is really slick. I can't wait to model this in foam or pine and see what it looks like in 3D. More to come.
The case for ATV drivetrain
Oft contributor and friend of Project Streetliner, Aaron, has more than once made the case for using the drivetrain off an ATV (or "4-wheeler" as we southern kids grew up calling them). At first blush, I've always hated the idea because I'm a scooter snob. I don't know ATVs and I don't care about ATVs. But there's one big factor that makes Aaron's case for the ATV drivetrain impossible to ignore: reverse. From his previous comment:
IMHO… I’d say to go with a small ATV engine for several reasons.
1) They are virtually identical to many motorcycle engines, except their gearbox has reverse, which will save you a lot of hassle later.
2) Many of the “manual shift” variety have an automatic clutch, which will gain you most of a scooter’s “twist-and-go” convenience while still keeping the ability to gear up simply by changing sprockets (something you can’t do easily with a scooter – see Craig Vetter’s woes with his Freedom Machine). Even if you decide to go with a CVT ATV instead of manual, you can still run a sprocket/chain off the bevel drive that normally drives the rear axle.
3) ATV engines are commonly larger bore single cylinders which are setup to generate a lot of low end torque, which will be useful after being geared up to your desired top speed. Many small displacement motorcycles don’t have a lot of torque and may have to be geared down to move a heavier vehicle then they were designed for as quickly as you’d like (especially if you decide to make it a 2 passenger trike).
4) Depending on what you decide to do about the front suspension, you may get many of the parts you need right off the engine donor.
5) If your EV desires grow, you can always retrofit it with one of the Motorcycle EV Conversion kits coming out lately. That option won’t be as easy if you start with a scooter engine/swing-arm/wheel.
6) And last, I don’t think the hp difference will be enough to limit you to surface street speeds with a gearbox to choose your final drive ratio. With a CVT or EV you have the problem of being “wound out” at your peak RPM and not able to accelerate further. Craig Vetter had this problem as well. With a gearbox almost any engine that will move you 55 with “power to spare” (as you dictated) will also get you to 70 for highway runs.
I really can't argue with any of this. Especially with many of the "sport" ATVs on the market today, horsepower won't be in issue. I wonder a little about just how these engines are tuned, given that mpg isn't your primary concern off road. They might be set a lot richer to allow for higher performance. If their carbureted, that's not so hard to fix, but if they're EFI, which most are these days, then getting that re-mapped could be quite tricky. I really only have two concerns: weight, and form factor.
Weight is an obvious concern, as the less weight the Streetliner has to haul off the line, the more efficient it will be. Some of this can be overcome with gearing and aerodynamics, but the lighter the better is a good rule of thumb. I'm concerned about weight in the ATV primarily because it's a 4WD vehicle. I only need to drive one wheel, so I'd effectively have a second output shaft and differential just getting lugged around with no purpose. The most mad scientist thing I can think to do with that second shaft would be to run an air conditioner compressor off of it or perhaps a second alternator. That has interesting connotations, but I'm still not sure.
The more troubling concern is that of form factor. What I've designed so far has a wheelbase about 4" longer than my MINI. Granted, the MINI is not a big car by any measure, but getting much longer than that worries me in terms of low-speed maneuverability. I don't want the thing to be so long it can't easily park. The guys who build those impossibly long chopper motorcycles run into this all the time. Their stretched-out bike can barely turn around coming out of a parking lot without doing a 12-point turn. I know that's hyperbole, but I still don't want to go down that road if I can help it. The scooter drivetrain has not just an economy of engineering simplicity and bolt-on convenience, it has an economy of space. Without knowing more about the ATV powerplant, I'm not sure if I can cram it in behind the seat on the Streetliner the way I'd want to. I doubt it's impossible, I just need more information.
So it's certainly on the table. I need to get some measurements and figure out which ATVs would be good candidates. Looking around online, the tricky thing is finding one that isn't shaft drive. For this to work, I really want to have the final drive be chain and sprocket so that I can adjust the end gearing as easily as possible. I guess we'll see.
Any thoughts?
