Autotricycle Design

Discussion in 'Off Topic' started by SimpleSimon, May 23, 2008.

  1. SimpleSimon

    SimpleSimon Active Member

    Since you said that, LF, I figured I'd show you where I am with design work on the dual rear-wheeled autotricycle design I started yesterday. Louisiana does not consider a three-wheeled conveyance a bicycle, and the motorized bike laws are quite specifically addressing "bicycles" (two wheels only). So far as I have been able to discover, three-wheeled bicycles (delta or tadpole) are a total non-entity under LA laws, which leaves motorizing one in limbo as well.

    The law does define an autotrike, and since I want a road worthy vehicle that meets my needs, I figure I'll just design and fabricate the d****d thing myself. As shown, it's just the bare ladder frame and the the rear subframe. Note that as designed, the rear subframe remains normal to the road surface whilst the front suspension and the ladder frame is leanable, to 35 degrees off vertical either way. In addition, the rear subframe is so mounted as to be able to flex vertically through approximately 3.5 inches (shock absorber controlled). I'll likely add more pics to this thread as the design process develops.

    Right now I'm contemplating a common axle with 3 hubs mounted for the rear - two 26 inch outer hubs and a 16 inch middle hub and rim moddified to run an industrial link belt from the jackshaft immediately behind the engine. I've found a new Robin America 5.5 hp 4 cycle engine for $199 ($0 shipping!), and will modify the engine mount between the pivot and the fender/shroud frame of the rear subframe as needed for that.

    Attached Files:

  2. That's gonna look cool.
  3. I've seen a recumbent like that. What's the advantage besides not having to balance?
  4. SimpleSimon

    SimpleSimon Active Member

    Fair question. The "not having to balance" part is. for me, the biggest concern.

    All trikes involve trade-offs. Trafitional delta trikes typically experience significant tire scrubbing, inside wheel lift, and other issues in turns at any speed at all, in large part due to the high center of gravity, and the mass distribution. Tadpole trikes with rigid frames experience similar issues when built with a conventional high COG.

    By incorporating into the design significant caster angling (I'm going for 12.5 degrees), camber of approximately 1.5 degrees (adjustable), and careful implementation of Ackerman angle steering geometry, those problems are greatly reduced. The semi-recumbent seating lowers the COG greatly, the locked pivot parallelogram front steering with active self-leveling and the leaning ladder frame and self-leveling rear subframe go further toward insuring consistent power delivery and non-scrubbing rear wheels.

    It's a process of trade-offs and compromises aimed at maximizing desirable characteristcs while minimizing undesirable ones.
  5. Alaskavan

    Alaskavan Guest

    I'll be following this thread. I have a small Wankel that I'm thinking about putting on a full size fully suspended tadpole.
  6. Eco Speeder

    Eco Speeder Member

  7. Eco Speeder

    Eco Speeder Member

    Wrong question perhaps; What's that advantage of 4 wheels over two?

    To delve into that further...Whats the advantage of 4 wheels with suspension that lean??

    Simon is working on a vehicle concept that is as potentially more revolutionary and as impacting than the automobile or airplane has been. Moreso perhaps. We need this now. The first autos were perceived as a rich persons nuisance toy for years.

    Once the various attributes of this design type are dialed in it will easily handle freeway speeds. The handling will make sport motorcycles seems archaic, dicey and dangerous.

    How does 95 miles per gallon and a driving experience that makes an expensive sports car seem like a dead lay register?:lol:

  8. Alaskavan

    Alaskavan Guest

    Simon, if it's not too much trouble, please post links to sites where you find important relevant information.
  9. JemmaUK

    JemmaUK Guest

    I do hate to be a killjoy, but I do see one problem with this build and thats the engine...

    5.5hp is liable to get the local cops bouncing around with joy especially if its that distinctive a machine...

    You get a nice friendly one whos not in the middle of a divorce and they might just stop you to have a look at the machine... you get the other sort and they'll try and hit you with every law they can think of...

    I do like the idea of a protected drivewheel but what happens if the chain/belt jumps and twists itself round the axle?

    Is the machine going to be pedalable? because if it isnt in most places it would be seen as a moped/motorbike and taxed/controlled accordingly...

    If you have something similar to SVA out where you are they will make it a royal pain to get that through just because of its unusual configuration...

    I just worry that you will finish all that work to get it on the road and then find out that even leaving it outside on the driveway will have every cop in the neighbourhood trying to be the first to ticket you :(

    Jemma xx
  10. Alaskavan

    Alaskavan Guest

    Jemma, I had many of the same concerns when I built my trike. So far the police smile and wave. If they told me tomorrow that I couoldn't ride it anymore, I'd still be happy I built it.
  11. SimpleSimon

    SimpleSimon Active Member

    As design work progresses, I'll be updating this thread, including links to relevant info found on the web. To adress the questions, I'll start by noting that this IS NOT a motorized bicycle design, it is intended as a motortricycle, and will be fully compliant with the legal requirements as regards lighting, signals, horn, rear-view mirrors, etc. HP limits are not an applicable concern in this design, however, I see no reason to overpower the design. Performance that will allow highway speed cruising, reasonable approach ramp acceleration, and such are what I'm looking at. By my calculations 5.5 to 8 hp is sufficient for those needs, mostly depending upon the final vehicle weight.

    Louisiana law addresses "autocycles", and requires a roll cage. So, I am researching the limits of body coverage that will keep it out of that category. A fairing and windscreen are allowable, but it can't be roofed, nor can it have side curtains/doors, not even fabric ones.

    There are three reasons for the dual tired design in the rear. Drive efficiency improves with a wider contact patch on the road, in high pressure tires. For use at highway speeds, a wheel needs excellent lateral force resistance, which a doubled rim with high spoke counts of heavy gauge will provide. In addition, by making it a leaning, self-leveling structure, the front suspension and main frame can lean into a corner, while the power train remains normal to the plane of the road surface, retaining maximum pavement contact for good traction. By placing the drive belt between the main rims on a modified smaller rim, all three co-axial and locked to the same rotational rate, it protects the drive belt, allows a fully tangential spoking of the drive rim, and allows dual rear disc brakes.

    Besides, it just looks COOL, don't you know.
  12. SimpleSimon

    SimpleSimon Active Member

    It has been rather hectic. I am still working on the motorbike design, with the idea in mind if modifying the rear subframe to allow for engine placement in a fixed position, relative to the rear axle. This will minimize high stress mechanical linkages, and will place engine mass directly in front of the rear wheel(s).

    In the meanwhile, I have finalized a couple more designs (I've found it works best if I put a project aside and let the questions percolate in my subcnscious periodically). One is a bicycle, designed with the idea in mind of (eventually) making it a motored bike (did you know that Troy-Bilt sells an EPA Tier II and CARB II compliant 4 stroke 32 cc engine, along with the rest of the device, as a string trimmer, for $149?). Again, a tadpole trike design, single spar (1 inch .125" wall 6061 tubing), with a curving head stock taken straight from the Troy-Bilt curving shaft string trimmer design, as pictured below.

    In this design, the rear wheel leans with the bike, but has freedon of movement (constrained) in the vertical, the front shocks are intended as a self-leveling mechanism, primarily.

    Attached Files:

  13. SimpleSimon

    SimpleSimon Active Member

    Well, I’ve continued to work at the design for the trike I want to build. Had to modify it considerably once I began doing some stress calculations, turning circle calcs, and leaning forces calcs. I am ready to begin building - first will be the main frame tubes, and getting them bent to the complex curves I want, then welded. Meanwhile I will be acquiring various production components.

    Some I will have to fabricate myself - the internal cable guides for the flex-shaft steering will be sintered bronze bushings in UHMW plastic centering frames, which will be cemented inside the steering tube every 6 inches. Nobody makes them, so I will. Probably the most difficult part of that process will be feeding the 5/8” stainless cable - it’s pretty stiff for wire rope.

    Basic trike spec’s are as below:

    Rear wheel 26 x 2.25 road tire, front 20 x 1.25 road tires

    Wheelbase: 61.5 inches L; 26 5/8inches W (30” at axle ends)

    Ackerman angle: 12.2 degrees

    Caster: 12.5 degrees

    Zero point angle: 12.3 degrees

    Camber: 1.5 degrees

    Main tube of the frame is 1 inch OD thick wall, as are the two subsidiary frame tubes in the front end. Steering header tube is 1.5 inch OD thin wall tubing, with a 5/8 cable flex-shaft centered for steering force transfer to the bell crank.

    Trailing arms are 4.5 inches long, bell crank is 3.5 inches. Steering range of pivot is 40 degrees each way from neutral, with lean angle being max of 35 degrees, damped by gas assist shocks.

    The rear wheel is constrained to remaining on axis with the bike frame, but has vertical flex through 4” max travel. As the trike leans, so will the rear wheel.

    Below are 4 views of a near final rendering, cleaned of dimension lines and colorized to give contrast.

    Attached Files:

  14. hlombard

    hlombard New Member

    Cool looking bike !!
  15. Jax Rhapsody

    Jax Rhapsody Member

    i see, your making it kinda like the Carver motorcycle. I like the design, if anything you could use a gokarts front supension. elinate the upper a-arm so it's got a foxbosy mustang style suspension or something. I have found trikes very unstable compaired to bikes or quads unless it has a long wheelbase. I may take a cheap walmart full suspension and make a offroad trike, only thing is with regular designs I think sideways movement would kill it. I love the dual rear wheel design and to answer a prevvious question; the only way the belt would slip off is if it were allowed to climb the rims sidewalls. If the belt is the same width as the spoke gaurd strip then it should be fine.
  16. SimpleSimon

    SimpleSimon Active Member

    Well, in terms of simplicity of construction combined with operational stability, the self-centering fixed-pivot parrallelogram front suspension is as simple as it gets, as well as being very economical of materials (and weight). The only contemplated innovation here is the steering linkage, and a somewhat novel shape.

    I have begun fabrication of the front suspension, and have the tubing for the front twin tube subframe. The horizontal ? shaped main spar tube will take a while - but there is a company here in town with the necessary equipment to shape the tube for me This one is intended as a pedal bike, to eventually be a motorized bike.

    The rendering I posted of the ladder truss twin tube main frame, with the co-axial tires, I want to build, but that is a later project. I'm still working on that design - because it is contemplated as an autotricycle with multiple horsepower from the beginning, it must meet much stricter construction standards to handle highway speeds and hazards. For one thing, designing in a crumple zone in the event of a frontal impact involves concepts I am still getting a grasp on.
  17. DougC

    DougC Guest

    I think you'll find that every state in the union considers a human-powered trike essentially the same as a bicycle.
    Is an autotrike a separate classification from a motorcycle? Usually states require a technical inspection for customized motorcycles, and bicycle parts aren't going to pass that inspection. You might want to email the dept of motors in your state and ask about this before buying any materials or parts.


    A lot of people have tried to build leaning trikes and most of them do it wrong, they basically copy the Trailmate Funcycle delta design, which is prone to bump-steer and not stable at high speeds.

    There have been a number of threads about tilting trike construction on the bentrideronline forums. The only design I've seen that would be stable would be one using free-to-caster steering, where the rider controls the leaning input only, and the wheels are allowed to seek whatever line they are leaned to. This might not work well at very low speeds or off-road, but should work on paved surfaces very well (as well as riding a bicycle no-handed does, but with better tilt control). You could build this as a delta or tadpole, but if you did it as a delta you'd have to figure out how to transmit motive power to the rear wheel(s). For an engine-only trike that's not difficult (just build the engine on the wheel's tilting assembly) but for a human-powered vehicle that's a pretty tall task. Chain-twister bikes are possible but most people (me included) lack faith in their durability.

    This is a thread I started there, with a link to the page showing what I had planned. I began building that trike but stopped because I don't think the bronze bushings I have for the front end will work well enough (they will cause the steering to be too wobbly). I could not find any source of reasonably-priced expanding bushings, and I don't have the machine tools to make them myself. I could possibly make them by hand, but they are a part that will regularly wear out and need replacement, so I don't consider that practical.


    Yahoo has a tilting trikes group, but I find that the Yahoo groups message interface quite simply stinks and for that reason alone I'm loathe to use it. It only threads messages ten or twelve levels deep, and then dumps anything else into the bottom level. I have wasted too much time already trying to follow threads there.
    Last edited by a moderator: Jul 15, 2008
  18. SimpleSimon

    SimpleSimon Active Member

    Thanks for the input. Especially the link to the thread at bentrider - lots to think about there.

    I am by no means a mechanical engineer - I am an utter auto-didact as regards engineering questions, and have little doubt that I am overlooking important issues, so the more questions anyone raises as regards my ideas, the better I like it. It's why I've posted them here. I've been working on this idea for more than a year now, because every time I've gotten a design tweaked to what looks good on paper, I build a model to scale, then start trying to improve it.

    I've learned a bunch in the process, and as is discussed in that linked thread, wheelbase width and CoG heigth have become dominant concerns. For my purposes, I am unconcerned about unpaved surfaces - it's doubtful I'd ever be on any more than momentarily. The way I look at it, if I don't try this, then I'll most certainly never have anything to ride approximating what I want. If I do, I may still not achieve my desires, but I can at least say I tried.

    Wheelbase, both width and length, have to be a compromise involving many factors - one of the most important of which is useability. Too wide, it might as well be a car, in terms of track, and it won't go places I want the bike to take me. Too long, in ratio to its width, and you WILL side-slip the rear wheel in cornering.

    CoG height is critical, and frankly the lower I can reasonably push it, the better I like it - but again, it's a compromise. It has to be useable - which means, practically, that once the front wheels have cleared a speed bump, and the rear wheel has not yet encountered it, I don't high-center my butt. In addition, of course, there is the rather critical concern of the lever arm forces resulting from having an unbalanced mass significantly above CoG - too wit, my person.

    Part of why I am looking at the rather unusual steering linkage I am contemplating is the concern over transmitted shock forces to my hand. My prosthesis is useful in steering, but frankly, at least 70% or more of all steering forces must be dealt with by my right hand and arm, as must be all non-steering control inputs (brakes, etc).

    I figure that I'll end up worshipping the old motto - ""If at first you don't succeed, try, try again!" For me, that is nothing new - I've been coping with just one hand since I was 12 years old, and believe me, you (unless you have similar issues) have little concept of just how very MUCH in life is blithely designed for two-handed usage. Heck, just typing this post is being done on a keyboard designed and sized for two handed usage, yet I can type 30 wpm on it with just two functional fingers and a thumb. So, finding a way to make things work for myself has ALWAYS been my reality - from figuring out how to climb a rope in gymn class, to working out how to make a hang glider work for me, to designing, building, and flying an ultra-light aircraft that I could control well.

    The one thing I've never listened to is - YOU can't do that. If I had, I'd have been an even more depressed curmudgeon at age 15 than I am now (in much worse health and fitbness) at 52. So, I'll experiment. If it doesn't work, still I'll have learned many things, still I'll be able to look in the mirror and say - those dings and scars were honorably earned. Worst case, I give up on building a leaner, and convert it into a fixed axis tadpole semi-rcumbent trike, and learn to deal with those attendant issues.

    Really, even if I manage to build something that kills me, so what? 90% of the joy is in the creation.