faired recumbent tadpole trike - design start

B

bobc

10 kW
Joined
Jan 20, 2011
Messages
993
Location
Knutsford England
I just started another project - as described above.
It seems to offer the best aero, safety & performance & range compromise for electrification.
Being a trike (3 wheel tracks, you can't steer round the potholes) & reasonably pacy it will need suspension.
So the rear swingarm pivot will also be the layshaft/jackshaft bearing (jackshaft will run on angular contact bearing pairs, swingarm will pivot on needle rollers).
The electrics will be LiPo, ESC & RC outrunner with belt drive to jackshaft.
I've designed some custom front hubs, outer bearing is dual row angular contact bearing, inner one normal deep groove bearing.
I've made the first purchase of mountainbike spring/damper units off ebay (850lbs/in 35mm stroke)

This was partly inspired by our greenpower racer, which we made using vacuum bagged composites, FRP over foam core shaped by our 3d router - does a lovely job & it's quite easy.... Those cars will take a person well over 100 miles at 30mph average using 80Ah at 24V. The faired recumbent trike is the nearest thing to one of these cars that you get to see on the road. My ebike uses more juice than this going below 20mph.

For the front sus I'm going to use the old beetle system but have the 2 sides welded together so there's total stiffness in roll - means I can easy take a crank to a "spine" mounted spring/damper and the tie rod can be a single peice affair with no possibility of tracking errors. I'll get pictures up eventually....

Not got very far yet...
trike.jpg
 
Hi bobc, I have made several commuting and extreme racing trikes and several 2 wheel extreme low riders for human power vehicle racing many,many years/Kg ago but recumbents have evolved a lot more and are even more radical and impractical now. I think faired trikes are great practical, safe , efficient commuter machines.
Have you lived with a trike before? They can be good and bad, riding down stairs or between things, or hoping up a curb can be a pain, but it depends a lot on where you ride.
A big problem with faired recumbents is the amount of room you need to swing your feet in the front of the ideal pointy naca section style body work. Compromises are often made with lumps and bulges that are hard to see over or holes and trap doors for feet and knees, small 150mm cranks etc. I say THROW AWAY THE PEDALS and make a smaller nicer simpler greener machine. This might raise a few eye brows but consider the human body as a muesli powered fuel cell. It runs at about only 23% efficiency it overheats and starts leaking coolant at around only 200watts of continuous output (based on NASA's fit male). Pedals, cranks, chains and sprockets have to be made massive and heavy for the high torque low revs of an engine that operates between only a 60 to 90 rpm window! so needs a 24 speed gearbox to operate in the efficiency ban its also fairly expensive for a good quality group set. So I'm suggesting no more hybrids just go full electric to save the planet!
As you no longer have this long heavy noisy chain whipping under your butt you can sit right on the floor. If you pivot your body back and slide your feet up more like a modern fomula 1 chassis it lowers your c of g of your body and allows you to reduce your front wheel track for the same handling as before. This reduces body height and width so smaller total frontal area and you can now use a thinner % NACA section for lower drag, and simpler lighter cheaper body work etc and you can still see over your feet as they are not going up and down and getting in the way.

Those spring rates seem very high for road use but it depends on active spring ratio etc. With such a low c of g body roll would be minimum.
For good handling think carefully about C of G of your body for and aft, its a compromise between cornering stability (all weight between the front wheels) and rear traction and braking, trikes can endo. For good steering feel at speed correct castor angle(i think i used a round 9 degree), and for bump steering feedback design zero scrub radius on king pin inclination, and use full ackerman to reduce tyre scrub while cornering.
Check out some of your favorite trikes and pinch some hard earned good ideas.
Have fun

Zappy
 
Nice input Zappy,

For those who want to get some exercise, or simply to add startup torque for a speedy machine with broad current limiting for its continuous smooth acceleration throughout a useful road speed range without introducing the noise, efficiency, and dependability penalties of multi-speed gearing, what about linear input for the human power? A bit of human input for those first few revolutions in stop-n-go traffic is a huge benefit especially using an ESC.

John
 
Thanks for the notes guys; on the "living with a trike" front, one of the guys in my office commutes by tadpole so I've been bending his ear a lot... BTW he reckons the trike is no more or less visible & therefore dangerous than his standard bike - but I do worry that he's been out of his car for too long & has forgotten the "glare" problems in spring & autumn; I still suspect a bike is not only more visible being taller, but has a better chance of being able to climb a kerb if necessary to get out of the brown stuff.
After thinking about it, I have several projects on the go which all need a current (therefore torque) controlled speed controller which will work from zero speed; that includes (to a lesser extent than the others) this, a commercial electric go-kart idea and the landspeed record car. So if I had an ounce of sense I'd make that go first (a project I started a couple of years ago!!!). So I'm going to put this on the back burner for a few months - I might drop the odd drawing on here from time to time, but it will be a while before I cut any metal.
Just for fun, here is a front hub detail; the outer spoke flange also clamps in the dual row angular contact bearing (that bit's stainless, radial spoked, rest of hub is ally, spoked cross 3). The bearing inner is held by an M12 fine bolt screwed into the 15mm DOM tube stub axle.
frhub.jpg

Lots of good advice in yr post zappy, thanks! I think I need to put the pedals in so that I only have to obey the electrically assisted trike rules, not the "quadricyle" (light car) ones. I agree it's a bit daft but it's preferable to live within the law & here I get to choose which laws to live within... I know just what you mean about needing a massive volume for pedalling feet (mine are size 13 BTW :^( You have to look over the top of that massive box with the feet in so the head has to be high etc. etc. Thanks for the 150mm crank tip!!! genius...
 
The front "foot and crank" area is a real problem on a faired recumbent trike, my own feet are over 350mm long and if you add that to double the crank throw you end up with a front on the machine well over 700mm high. If your eyes have to be over that height, you end up with a monster machine that just cannot be very good aerodynamically. The answer is obvious - go for a treadle design. I have a plan with the pedals mounted on linear bearings and 3 separate 8mm chains in 2 planes to take drive to ratchets on a more conventional bottom bracket. At a stroke, front height reduces below 400mm & the project becomes practical once more ;^)
 
Vision isn't as bad as you would expect, I have built a couple of corflute shells over production trikes and vision was never a problem, aerodynamically they are very clean being teardrop shaped.
 
This one isn't faired but has always inspired me:http://www.recumbents.com/wisil/wianecki/leaning_trike.htm
The leaning part is awesome, takes away some of the disadvantages of a trike.

About your hubs - if it's going to cost you more than about $100 per hub, consider buying an off the shelf Cannondale Lefty hub. They're already designed for one-side mounting. You'll have to machine the axle, but that should be easy to specify and or fabricate.
 
It might turn out to be quite an interesting development this; the idea was born as a way to get a "greenpower racing car" legally onto the road. Those cars travel 120 miles on 20pence worth of electricity - that's an equivalent of 3500mpg (UK) If speed is reduced to 16mph to make it legal (again, UK....), effective mpg will increase to closer to 10000 - the sort of figures they get in the shell eco-marathon. But this is on a road legal commuting device. Performance of a faired recumbent far exceeds an upright bike anyway, and the fairing goes some way towards keeping the driver clean & dry - the electrics stop him getting sweaty on the journey. No tax, insurance, SVA rules etc. etc.
I have an efficient diesel car, but fuel for it alone costs over 10pence per mile. This thing will be closer to 0.1pence per mile - an improvement factor of about 100.
Maybe you can see why I'm fixating on the treadles and visibility - to be practical on real roads, you need to be able to see the potholes, and the aerodynamics is key to making the concept work.
Here is part of the treadle system. Complex but hey ho - not too bad, or heavy or hard to prototype :^)
pedalassy.jpg

PS - this thread is clearly in the wrong section - sorry mods - should it be moved to ebike general?
 
bobc said:
PS - this thread is clearly in the wrong section - sorry mods - should it be moved to ebike general?
Click to expand...
Is it going to be a hubmotor drive? If not, then I'd say this section is fine. ;)

but I can move it if you want.
 
OK - I do plan outrunner -> layshaft -> left side rear wheel system like I put on all my bikes. Because I want LEGAL and I don't want gears on the electric side, the plan is to use a motor that's more like a kilowatt & do a controller where the motor amps (therefore torque) is inversely proportional to volts (i.e. speed) over quite a wide range. So I stay under 250W mechanical power out, but I have that power at all speeds from 5mph up to 15.6(the limit). So it's like I have an electronic gearbox. I just did a maximum power point tracking solar battery charger & used an AVR tiny5 to do the clever bit - thats a proper 8 bit microcontroller in a miniscule SOT23 package with 6 legs - costs 28p - I reckon I can use the same thing to limit motor current on this - the nice thing being that a kilowatt of RC outrunner is small, light and cheap (but big enough to get a toothed belt pulley on the shaft.......)
Oh yeah - the layshaft will run inside the pivot for the rear wheel suspension - that's final drive tensioning during bump sorted!
This thing will be years in the making...... unfortunately..
 
Stop press - I just cut short the whole development process by buying a 2nd hand KMX trike off ebay. I can fit the treadle system directly to that.
It's a start that will shave a year off the initial development - excellent - I might be running it within a couple of months!
And I can put it back together as "factory stock" if I ever want to sell on ;^)
 
Not so sure about tilting - it stabilises a tall trike and makes things easier for the wheels, but as I'm looking for best aero performance so it doesn't really work for me - I'm shooting for as low as possible, hence the treadles. I got most of the hardware lasered for the treadle system already, now looking for bigger front rims for my new trike - I'll raise the front axle to keep it low.
 
Here's a link I had saved. It's a DIY rear suspension tadpole, and the main theme is that there was no welding (once assembled and verified to meet goals, can easily be welded by any competent local muffler shop, aluminum can be DP-420'd).

I don't like how small the two front wheels are (easy to change). I thought there were several clever applications of junk bike sections. Ex: two childrens bikes head-tubes as front wheel pivots, but set to the proper angles, etc

http://www.youtube.com/watch?v=oyZWC1PeReA
NoWeldTadpole.jpg
 
OK - bit of progress; the 26" wheel I built now has a tyre on & fits in the frame just fine - I could fit a slightly bigger tyre at a pinch. Today my brother welded up the treadle guides (all made in stainless). I've started turning the readle rollers & bought a a small stack of ebay ball bearings for 'em. I'll have to see if I can borrow a set of RH & LH thread pedal taps from my LBS (I can live in hope....)
I'm a bit stymied because the 36 hole 16" (349) rims I wanted from sjs cycles are out of stock for a month or two - anybody know of an alternative? All the brompton rims are 28hole - I'd be more than happy with an un-drilled pair of these..... If anybody has a couple of 349 BSD rims on 36holes I would be most interested?????
 
Motor and jackshaft mounting hardware now designed & ready to be laser cut. The bearing holders for the jackshaft might be of general interest - I'm using a system copied from a CNC router project for clamping a deep groove ball bearing race supported on stainless laser cut chassis clamps; promises to be very cheap simple and adjustable. Also, as I keep pointing out, available to everybody - just about every town in the world has a laser cutting firm.... I hope my system will give some ideas to folk (who often perceive an RC build as difficult & ends up expensive)
Also I finally got the programming to work on the ESC/hall throttle interface board http://endless-sphere.com/forums/viewtopic.php?f=2&t=47220 and ordered a couple of $16 RC ESCs to drive it all so the trike has become the "guinea pig" for the "legaliser" board. I'll buy the toothed belts & pulleys over the next day or two & put assembly pictures on here.
The treadle rails & support are all welded up now, I have a stack of rollers to turn bearing seats into, then I can think about bolting that on as well - probably a few weeks off if I'm honest ;^)
PS - took the trike to a family get- together & the kids all thought it was brilliant fun. On the other hand I went for a pedal down the road & was not prepared for all the road dust that passing cars kick up - on a DF bike you're above all that stuff.....
 
got the stuff back from the laser cutters. This is the motor mounting hardware
motormounting_zpsa41769d4.jpg

This is the hardware to mount the jack shaft. Those are ordinary deep groove bearings (12mm)
jackshaftbearings_zpsaa421677.jpg

and here they are loosely assembled on the trike frame
mechanics_zps0b09ae7c.jpg

What you see there, the motor cost $30, the bearings £2.12 each and the laser cutting £10. The various screws were 50p ;^)
Obviously all belts & chains are tightened by sliding the parts along the trike frame.
I'm also making progress with the treadle assembly - pictures to come
 
here are the taper lock motor pulley parts
motortaperlok_zpsdf9d692a.jpg

I got the 2 5mm toothed belt pulleys from lakehurst in UK for £24 delivered. Quite a bit cheaper than HPC. The big pulley had no flanges and the boss & pilot bore were WAY off centre (like best part of a millimetre) Fortunately I wanted to turn all that off & the pulley is now good, accurate & about 1/2 its original weight. Or less ;^)
Oh yeah - the motor pulley is 15 teeth and the big layshaft pulley 72 teeth. So I have about 5:1 primary reduction. Motor rpm is 25 * kV = 6750rpm so the layshaft will be doing 1406rpm. The wheel has about 2m circumfrence so a mile is 804 revolutions. so at 20mph I'm doing 20 * 804 revs per hour = 804/3 rpm = 268rpm. So I need secondary gear ratio 1406/268. I have an 80 tooth wheel cog so I'll need around 15teeth layshaft cog.
 
more work on the hardware: here's the treadle rail assembly (the idler/balance sprocket is fitted)
treadlerails_zpsd204de00.jpg

this is the electric drive hardware
trikedrive_zpsa577a84e.jpg

and a slightly closer look at the motor & primary reduction
trikedrive2_zpsdf8d39f7.jpg
 
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