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deanp
Starting Member

Indonesia
2 Posts

Posted - 04/10/2015 :  06:28:28  Show Profile  Reply with Quote
I've built a tilting sociable quad by joining two highracers with pivoting arms to form a parallelogram. The result is rideable but steering input doesn't give good lean response. The little information that is available suggests a damper is required on the lean angle, which I have but so far this hasn't been a complete solution, although my damper is a bit crude which won't help.

Anyone built anything similar and have any input? The bike is in an early stage of development so I'm still working out lots of issues.

deanp
Starting Member

Indonesia
2 Posts

Posted - 04/22/2015 :  08:10:28  Show Profile  Reply with Quote
Not any response but I'll give on update on progress. Have got the some of the handling issues sorted out. I had been going backwards as each pass of strengthening and improving the alignment on the frame made the vehicle less and less rideable. Eventually I went back to the configuration that worked best when the headset mount had broken, and raked the front end to 60° to give a massive 20cm of trail. The steering went from being unresponsive to giving reasonable control. Interestingly for the frame geometry Bill Paterson's trail formula calculated 24cm of trail. Steering is still fairly light, which is fortunate as the handlebar is mounted directly to the forks in an underseat position and there is a fair reach to the bars.

One unexpected benefit of the extreme rake is that the arc of the front wheels combined with the narrow track width gives a pseudo-ackerman compensation so there is no tyre scrubbing going around corners. This doesn't work backwards and it scrubs quite badly.

Additionally the cables on the dampeners for side to side lean where rubbing so I cleared the path for these. The extra friction was giving too much dampening, so I couldn't lean correctly to maintain balance. Although not required for straight line riding I added some light springs to help resist lean at large lean angles, which prevents the vehicle flopping into corners. It seems that either springs or dampening will work to control the lean. The key consideration is that from the limited amount of info i have is that a leaning quad has a tendency to flop into corners in a way that cannot be easily corrercted for by steering action alone, as occurs with a bicycle. So dampening/springs are used to slow/reduce the leaning force to a level were steering input can give the correct lean angle.

These modifications changed the quad from unrideable to successfully weaving through a figure of 8 course between pot plants in my front garden.

While rideable the quad is still not as maneuverable as a bicycle, and is not as stable in a straight line. This prototype doesn't have very good alignment which won't help, but I will try raising the seat back to 40° from 20°, and experiment with more trail.

Final points are I'm happy with progress to date that the basic concept works, although I haven't tried the sociable with 2 people yet. I'm looking at different materials to build with. Have been using giant bamboo with plywood to give rigidity. While giant bamboo is strong enough, it lacks torsional rigidity, and is difficult to join. Bamboo may work for diamond frame with it's acute angles and rotational stressed spread out across the entire frame, but it's much harder to make that work with a recumbent. Probably just easier to go with steel for the next version, if only it's much easier to make stiff joints.

The other point is that with the highracer configuration I'm having alot of heel strike issues. I can only assume that most highracers are not designed for the street. I'm aiming this to be a commuter, hence lots of sharp turns and stop/starts. I've got 80cm seat back to BB distance which feels comfortable for stop/starts but doesn't leave much wheel clearance, even with the seat mounted quite close to the steering head. And I'm 6'2" tall so no shorty. To clear the wheels i am going to have to go with a fairly high seat height, which is good for traffic, but means that I'll have to perfect a way of locking the lean so that feet don't have to touch the ground. Which has been difficult to do so far.
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Larry Lem
human power expert

South Sandwich Islands
2523 Posts

Posted - 04/22/2015 :  11:11:35  Show Profile  Reply with Quote
Cool!

Pictures?

Larry Lem
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PUGZCAT
recumbent enthusiast

Canada
459 Posts

Posted - 10/18/2015 :  15:15:24  Show Profile  Reply with Quote
As I recall some folks in Toronto Ontario Canada built a four rider back to back sociable leaning quad. There was a video or two on YouTube. They could have also built a back to tandem with 2 wheel drive and snakey independent 2 wheel steering. They rode the stuff on Critical Mass rides, it's worth a Google search or two, to see. They used steel in the builds. They also may have helped to build the pedal powered quad "79 Buick Regal that the police pulled over and said was unsafe, video on also on YouTube 10 years ago. Best of luck sorting things out and happy building and safe riding.
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