The Kneeslider

Doers Builders and Positive People

How To Drive and Steer the Same Wheel in a Two Wheel Steering Motorcycle

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Split hub center steering drive wheel on Bob Horn's recumbent racer
Split hub center steering drive wheel on Bob Horn’s recumbent racer

Last summer we showed the latest version of Bob Horn’s recumbent racer with two wheel steering. If you’re new here, Bob’s race bike is his own design and entirely scratch built and when you decide to incorporate 2WS, you can’t just look around to see how everyone else did it and choose the method you like best, because recumbent 2WS race bikes are non existent. So Bob thought about the problem, came up with a solution, fired up the metal lathe and got to work.

Machining in progress on one half of the split hub
Machining in progress on one half of the split hub

He has a nice explanation on his website with photos of his “split hub center steering” assembly and his engineering looks both well conceived and beautifully executed. Of course this leads to a logical next question, if you can steer the drive wheel, why couldn’t you drive the steering wheel? As you might guess, Bob is already thinking in this direction which means we could see a 2WS and 2WD racer. Stay tuned.

The split hub steering and drive assembly
The split hub steering and drive assembly

Link: Rohorn

Comments

  1. This is awesome to see! One question for rohorn; it looks like you are using a universal joint to accommodate the change of steering angle. Do you think you will get much vibration when the joint is driven at an angle? I understand that a CV joint can transfer torque at large angles without the acceleration/deceleration changes that occur in a u-joint. Excellent work though, looks like fun.

    • Its a pretty small angle. I think the speed variation (as a portion of total speed) is proportional to 1-cos of the mis-align angle, so there shouldn’t be much for small angles (say 10-15 degrees). For the front, a CV would probably be better.

      Also seems like it would be easy(ish) to incorporate a cush drive. A lot of shaft couplings that allow mis-align (though not usually 10+ degrees) are essentially just cush drives that can flex a bit as well. Then again, with an ex500 engine, it may not matter much if there is a cush.

    • Todd,

      Thank you!

      Excellent question – that was an immediate concern! The rear end only steers about 6 degrees on either side of center, with only a fraction of that seen at speed. The velocity variations (?) at those angles seemed too low to matter. That said, with the cush drive left off, a combination of angular velocity changes and power pulses (?) made me wonder if the chain would go nuts at certain speed/corner/gearing/etc… combinations. So far, the system is behaving itself. There’s also the good possibility that I haven’t ridden it hard enough to find out…

      Sebastion,

      Thanks! Yes, the EX500 engine’s less than terrifying production of power isn’t terribly revealing of drivetrain problems. A CV joint IS the ideal design solution, along with an independently located upright. That would also allow single sided wheels – rapid wheel swaps would be welcome, and that would look sooooo cool! But all of that would be a fabrication nightmare with the fabrication tools on hand – one of those “What’s the best I can design?” vs. What’s the best I can produce for the time/money/tooling/etc… on hand?” situations.

      For the next one, steering angle at either end will be15 degrees on either side of center.

      • I’m not so sure CV joints are a good solution for motorcycles. My dad and I have done some experiments and they resist changing angle if they’re under any load. Meanwhile a U-joint is low friction, and you only feel the vibration from it if you’re using high power at a large steering angle. (i.e. crawling over angled logs, or burnouts in a circle)

        Btw, the first AWD motorcycle I made was a modified RC motorcycle. It used a suspension very similar to what Bob’s made. I always thought it would be a good design for a road racer if I ever made one.

    • Then I thought about how the wheel isn’t turned much at all when riding under power

  2. Initially, it looks like a very good potential design. Just wondering?, about the extra stress that is put on
    the final drive chain system.

    • There’s no added stress on the drive chain – nothing is affected by the steering. The final stage is connected to a narrow jackshaft mounted to the swing arm – tension never changes with suspension travel.