Human Electric Trike Thesis

Design of an electrically assisted human powered trike

Homebuilt Aluminum Trike

Posted by Bob Dold on Monday, May 29, 2006 3:47 PM

Pictures of homebuilt fully suspended aluminum trike of Julian Edgar from TrikesDigest

Quotes from builder:

OK. I’ve been for two decent rides on new trike. Problems are:

– Dampers rattle. That’s because they run standard rose joints in each end that don’t provide any rotational stiffness, so they flop from side to side within the brackets. Proposed solution: rubber washers each side in the mounts or alternatively, replace rose joints with rubber bushes – which would also reduce vibration transmission as a bonus.

– Gears slip. I am not sure if this is the derailleur settings, the internal 3-speed hub settings or the fact that the rear wheel (and so cluster and internals) I bought secondhand. The cluster shows some wear and I am using a brand new chain. Does that make it likely slippage will occur? I’ve done quite a lot of adjustment without getting rid of the problem which occurs only at very high pedal torques.

– Brakes are uneven. (I am using one lever hydraulic.) In normal use they’re fine but in a rear-wheel lifting stop the trike tends to swivel. Paul Sims of Greenspeed suggested that the pads may not have bedded-in equally. However, I think I’ll fit another hydraulic lever and run them independently. That’s primarily because I suddenly realised that one hydraulic system has no redundancy, but it also fixes the uneven braking as well.

Steering doesn’t have enough feel or self-centre’ing. I am not sure what to do about this: all the automotive textbooks suggest that you should _not_ run centrepoint (ie zero scrub radius) steering because it will make the steering heavier at slow speeds (and, reversing that, it will presumably hinder self-centre’ing). I can increase castor (I have adjustment) and – at a pinch – change scrub radius away from zero, the latter being more work.

Steering levers are too close to the centreline. This just means my hands are a bit close to my body – easily fixed with new steering levers, which I can do in 2 weeks when the welder comes back from the desert goldmine.

Body roll. I have been doing some high speed bumpy corners and it sits beautifully but the roll is a bit disconcerting. In terms of the suspension travel the roll uses up, there’s not a big problem (there’s plenty left for bumps) but it just makes the trike feel less sure. However, the only way I can think of containing body roll (without increasing bump damping or spring rates; both are otherwise fine) is a steel sway bar, which will add (even) more weight.

Talking about it… weight. I measured it again this evening and it’s over 30kg – about 31. I had intended for some time to have the frame sandblasted (or alkaline dipped) to thin down the wall thicknesses (especially in the seat frame which is about twice the wall thickness I wanted – I couldn’t get thinner wall thickness tube mandrel bent). Does anyone have experience of this? I understand you need to select the sandblaster with care otherwise with aluminium the result will look terrible.

About steering: a (perhaps serendipitous) side effect of the direct
steering as seen in the MR and Tri-Sled trikes is that moving the
steering arms from side to side makes the wheels turn quickly, while
push/pulling them results in a kind of micro-steering. Simple as it is,
this results in an amazingly stable high speed behaviour. Oddly enough,
the lateral movement actually gives the slowest ratio. When
push-pulling, the lever arm is shorter: slight, well controlled pressure
on the steering arms suggests the trike to wander left or right. Rather
good at any speed from 5 to 100 km/h.

Direct steering would of course defeat the purpose of full suspension,
but one could think of ways of implementing this principle of different
lever arms in several directions into an independent steering design. I
would think that ergonomically, the more precise movement has to be
controlled by the most powerful muscle groups.

Steering ratio is something important which definitely can be inproved.
Most things pivoting tend to have a decreasing ratio, unfortunately.
Julian, why don’t you let your light shine on this one?

Right now the high speed steering in our velomobiles is rather a
question of just ‘thinking’ left or right.

The only proper thing I could come up with is a rather complex design
consisting of cables around an ellipsoid axle. Ockham’s Razor prevents
me from going on with it.

end quote

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2 Responses to “Homebuilt Aluminum Trike”

  1. Justin said

    To improve the streeing you need to ‘toe’ you wheels in. To form a very mild V shape (the point of the V to the front of the bike. This will make the wheels self centering. Too much toe will cause to much tire wear. Toeing your wheels out make your trike want to shoot off in another direction

  2. joe dupont said

    amazing.. why not drive the front wheels? it would seem that this would be easy, especially if you used some king of spring coupling so that they don’t bind up in the corners.. just a thought.

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