Swing arm leaning trike

[mcw0]

This is my first post here. I've always been fascinated with leaning trikes...specifically tadpoles. I've never seen one with swing arms. My idea in simple terms is to take 3 bike frames. 2 of the frames you cut off the back, aft of the seat post. The remaining frame you do the opposite, cut off everything forward of the seat post. Now you have a common pivot for all 3 frames at the crank. I started blocking out this idea and immediately ran into tire scrub as the unit leans. But I came up with a gear system that can adjust the distance of the swing arm pivots from centerline based on the angle of lean. Intuitively, this seems like it should work since friction would work against tire scrub so it shouldn't take much force to slide the swing arm pivot along a shaft.

I'm not an engineer. Just a hobbyist. Can someone more educated than I in mechanical engineering tell me why this idea won't work? I'm assuming this won't work because everyone else has gone with some system of control arms for the front. Please see my simple animation.

I can't attach mp4 files.

For a lean angle of 45 degrees, The swingarm pivots a little more than 10 degrees in my rough layout. And the swing arm pivots had to slide inboard a little over 7 inches along the rear axle. The slotted gear (in green) pushes the pin on the swing arm to locate the pivot. Obviously, there would be another set for the other side. This is just a very rough proof of concept. The front forks should account for any bumps in the road while the swing arms deal with the tilt. I'll have to figure out the steering (hopefully with ackerman).





Ultimately, I'd love to build an electric commuter (once we're working back in the office again). I'd have to abandon the common pivot point for packaging reasons. And I'll have to make sure my gear system is located high enough as to not contact the ground. I have ideas on how to lock the tilt system. I'm getting excited about this idea so someone please shoot some holes in it and bring me back to reality.

Thank you for your thoughts. And I wish everyone a much better 2021.

 

[amberwolf]

Something to consider is that if the gears control the leaning directly, they also take the full loading of any torque in the process, so they have to be strong enough for that. I don't know what kind of loading that would be, so I don't know if you need anything special in the way of materials/etc.


The longer the distance from the pivot to the wheel, the greater the forces will be. (which is why a longer lever lifts weights or pries things up better than a shorter one)


A reason for using hte "control arms" rather than a design like this one is that with this, you change the angle of steering for each front wheel relative to the other, which may cause undesired operation during cornering. You may need to build it to find out exactly what will happen with the specific parts you will use. You'll also need to ensure you use two identical frames and forks and wheels for the front. Any differences in them may cause further undesired operation; worse the greater the differences.

 

[mcw0]

amberwolf

Thank you very much for your reply. You bring up a very valid point about the lever effect. My thought was the gears only adjusted the pivot location. They do not have anything to do with the tilting. I was thinking like on a regular bike, the tilting would be initiated/controlled by the rider. Not having ridden a tilting trike, I don't know if leaning into a turn is any different than on a bike. Plus I figured if cars can have differentials, then there has to be gears stout enough for this purpose.

My "simulation" had the tilt go to 45 degrees which automatically resulted in 10+ degrees of rotation on the swingarm. I just used the gears as a multiplier so that my slotted gear can position the pivot.

I know what you're saying about the steering. I haven't really thought that part out past "how do I steer 2 bikes with one control through a tilt?".

 

[mcw0]

I think I'm going to have to rethink my tilting being initiated by the rider/driver. On a bike, you are rarely dealing with much more than just your body weight. Maybe an extra passenger at times. But if I'm going to create an electric commuter, then I'm looking at a couple hundred pounds of hardware at least. That doesn't seem controllable with a rider's body weight alone. Any thoughts?

 

[JimVonBaden]

I think it is controllable, so long as you keep the mechanical center of gravity low. On a motorcycle, there is often 500 pounds of rider, passenger and gear high up. This is not a control issue as the rider and passenger lean with the turn. A leanable trike like you propose will handle it fine.

As to the gears, just make sure that ALL of the mechanicals and motor lean with the gears. No issue.

 

[mcw0]

Thank you for your reply Jim. Now to figure out the steering.