## Linear drive for hulled recumbents

### Linear drive for hulled recumbents

I started mentioning the idea of a linear drive here in this thread:
viewtopic.php?f=28&t=17847

I don't want to hijack this build log and therefor start a new thread to explain it a bit more.
Warning: This is not related to electric bikes in specific!
It's a way to be able to build a much smaller front hull to gain lower air drag. And probably a smoother torque curve than crank-pedalling offers.
I found an old drawing of the concept and I even found a linear drive I've once built for a similar project: A two cylinder boxer-motor without crankshaft.
Maybe from studying the pics you'll understand the way it works much better than from my poor explanations:

Please don't start discussing the boxer motor. I added these pic's to demonstrate that a linear oscillating move can be turned into a constant rotation.

-Olaf
Attachments
lineardrv.gif
left side view of recumbent linear drive. The green rectangle is the left pedal running on the blue rods. The chain is connected to the pedal and (in grey) also to the right pedal assy not shown. This helps to get an oscillating back/forth move. The freewheel bearings are orange. The bigger sprocket goes to the rear wheel.
piston assy of the 2-cyl boxer
gears2.jpg (91.2 KiB) Viewed 2228 times
Here you see the offset between the racks and the two gears with freewheel bearings inside
gears.jpg (90.5 KiB) Viewed 2228 times
gears added to the drive shaft. freewheeling both in the same direction
pistons.jpg (59.5 KiB) Viewed 2228 times
One gear combs one rack
pistons2.jpg (91.37 KiB) Viewed 2228 times
The whole assy without cylinderheads, I'd like to make a video of it moving, but I'd need three hands for that :(
olaf-lampe
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### Re: Linear drive for hulled recumbents

Hi Olaf,

You can make scale illustrations in Blender. Not CAD, but very handy.
Trailmate-blender1.png (200.26 KiB) Viewed 2213 times

I like the design of the motor for pedals. The concept should work well inside a velomobile.

Your thoughts on linear pedal motion versus elliptical? Some say elliptical should be more "natural" and less tiring.
Have a Nice Day,

TD

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TylerDurden
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### Re: Linear drive for hulled recumbents

I must confess, I'm living in my own little world. Not looking much over the fence, what others have done.
Occasionally I come up with a 'brilliant' idea. Only to find out later, it has all been done. ( see the ball worm drive thread )
Can you point me to some informations about the elliptical drive? I sounds like it either has a smoother torque curve OR reduces head room for the front hull.

I like the design of the motor for pedals.

The boxer wasn't meant as bike propulsion. But there are linear electric motors that could be combined with my linear drive!
-Olaf
olaf-lampe
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### Re: Linear drive for hulled recumbents

More here:
http://www.aist.go.jp/aist_e/museum/science/17/17.html

Much more on google image search: "linear drive", bike.

I think the linear drive benefits are good for inside a hull. I also prefer the simplicity compared to the system illustrated above.
Have a Nice Day,

TD

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### Re: Linear drive for hulled recumbents

Wouldn't it be better and more efficient to use 2 of the mechanisms for rowing bikes (one for each leg) to create the linear drive? They're supposed to be more efficient than derailleur type set ups, and have wider gearing range. I'm a bit unclear about how Olaf's linear drive attaches to the bike chain.

What I like even more than the smaller frontal area is that it gives you better option of foot placement while not pedaling, so you can even have your feet side by side or anything in between one at full extension at full retraction. That seems incredibly more comfortable than cruising motor only with feet on the cranks.

I also like that the pedal assembly can be much lower without worries of pedal strike.

Linear drive sounds ideal for ebikes with pedal assist instead of motor assist.

John
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### Re: Linear drive for hulled recumbents

@John
If you want independent pedal motion, it would make my whole construction easier. The bad point is, you'd need 'click'-pedals to pull the pedal back to the starting point.
'Click' pedals is something you wont like on a recumbent other than a trike. At least in city traffic it would be a high risk.

What I don't like on the rowing bike is the top steering. I like under_seat steering, because the hull can be much smaller.
-Olaf
olaf-lampe
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### Re: Linear drive for hulled recumbents

A couple of years ago I was tempted to build a recumbent, faired, electrically assisted tadpole trike. After a bit of CAD doodling I found that the pedal arc, particularly the need to allow enough heel room, was a serious limitation when it came to getting a nice shape and low frontal area. In my case, I wanted to keep the ability to pedal to avoid the need to register the bike as a motor cycle. I never had the wit to think of getting rid of rotating pedals!

During the electric boat project I have come across another linear pedal system that might work. It uses cables and one-way clutches to turn linear motion into rotary. Here's a link to a thread on the Boat Design forum that has some photos: http://www.boatdesign.net/forums/boat-d ... post219124

I'd thought of a variation on this basic idea, using lengths of toothed belt rather than steel cables. These could be wrapped around pulleys, fitted with internal one-way clutches driving a common shaft, to give semi-continuous rotary drive.

Jeremy

PS: There's a link from that pedal boat thread above to this: http://www.classicrendezvous.com/images ... loseup.JPG
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### Re: Linear drive for hulled recumbents

Olaf,

Actually I already thought that through and wouldn't want independent strokes (optional maybe, but would have to try first). The freewheeling would cause you to inherently go to full extension of both legs when yours legs aren't adding assist. The easy solution is a cable around a pulley tying the pedals to equal but opposite stroke positions. I think it will still permit more comfortable static leg positions, eg at half stroke equal extension.

On my current bikes it's impossible to keep up with the motor, so at cruise I ride with the crank near horizontal with one extended forward and the other rear, which gets uncomfortable. Feet at or near the equal position around mid stroke would make far more comfortable foot pegs for me, and I'd venture to say it would be even more comfortable than motorcycle pegs since they aren't in a fixed position. The linear stroke also opens up the advantage of adding fixed footpegs down below the stroke line without getting in the way like with circular cranks.

This is something we need to pursue.

John
Last edited by John in CR on Sat May 08, 2010 8:02 am, edited 1 time in total.
John in CR
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### Re: Linear drive for hulled recumbents

Jeremy Harris wrote:...I'd thought of a variation on this basic idea, using lengths of toothed belt rather than steel cables. These could be wrapped around pulleys, fitted with internal one-way clutches driving a common shaft, to give semi-continuous rotary drive.

Jeremy

Jeremy,

Have you already thought about how to attach the pedals/pegs to the belts with a reliable connection? Pegs with rollers secured on a track seems easy enough. Maybe a retro-direct type of chain arrangement could be useful, and substitute a cable for the part of the chain going to the push pegs to keep things quiet and compact. That opens up common and cheap bike parts for a test.
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### Re: Linear drive for hulled recumbents

Do all of these approaches, including the one in Olaf's initial post, all share the one significant flaw with retro-direct? That is a bike that cannot roll backward at all. I think they do.
John in CR
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### Re: Linear drive for hulled recumbents

John in CR wrote:Do all of these approaches, including the one in Olaf's initial post, all share the one significant flaw with retro-direct? That is a bike that cannot roll backward at all. I think they do.

If they are driving a rear hub with freewheel?
Have a Nice Day,

TD

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TylerDurden
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### Re: Linear drive for hulled recumbents

TylerDurden wrote:
John in CR wrote:Do all of these approaches, including the one in Olaf's initial post, all share the one significant flaw with retro-direct? That is a bike that cannot roll backward at all. I think they do.

If they are driving a rear hub with freewheel?

Freewheels allow forward rolling. To roll backward, the cranks must turn backward. That's the one significant flaw with R-D, the opposing freewheels prevent the bike from rolling backward. I believe it will be the same here.
John in CR
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### Re: Linear drive for hulled recumbents

Yes John you are right. I tried to turn the shaft of the boxer backwards and it didn't work. You'd need to add a clutch somewhere or simply lift the rear wheel

Thanks Jeremy for joining in with these additional informations. The looong cranks from the bike are not helping to reduce the hull size but it's worth a try in a normal frame.
Maybe we should start a craziest pedal propulsion contest
My favoured so far is the tandem rowing bike, this is soo sick.

-Olaf
olaf-lampe
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### Re: Linear drive for hulled recumbents

I think that the long cranks could be removed easily, just replace them with linear slides for the pedals, like the stuff used to build slides for CNC machines.

I'm not sure how ergonomic linear track mounted pedals would be, but it would keep things compact.

Jeremy
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### Re: Linear drive for hulled recumbents

I've seen common wheelchairs with some kind of pedal drive. I was searching pictures of them to check if the linear drive could be useful there, too.
I found this:
Think of a linear drive mounted like a benchpress or these loong curbs from Jeremys second link.
Attachments
rolli2.jpg (61.45 KiB) Viewed 2073 times
olaf-lampe
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### Re: Linear drive for hulled recumbents

olaf-lampe wrote:Yes John you are right. I tried to turn the shaft of the boxer backwards and it didn't work. You'd need to add a clutch somewhere or simply lift the rear wheel

Thanks Jeremy for joining in with these additional informations. The looong cranks from the bike are not helping to reduce the hull size but it's worth a try in a normal frame.
Maybe we should start a craziest pedal propulsion contest
My favoured so far is the tandem rowing bike, this is soo sick.

-Olaf

A a single rowing bike with a fairing should be able to break the 81mph HPV world record, since you could transfer so much more power to the wheels than pedal alone via legs, back, and arm muscles, just like rowing. Once you make it a tandem, it should be able to slaughter the record by a wide margin, since you gain almost no additional wind resistance but double the power and can make the power transfer continuous instead of discontinuous. I'll leave coming up with that kind of thing to you cyclist guys. In the meantime, I just want to break the HPV record using an electric motor, which should be a matter of simplicity. I also have a both a current bike build as well as the next one in line where I see a linear stroke as great benefit in terms of space and comfort.

An electro magnetic toothed clutch/brake as the clutch for this mechanism to allow reverse might be ideal. Then unpowered would be engaged, and in those rare events you need to roll backward it uses a bit of juice. I can foresee instances, like stopped or parked on an uphill, where the inability to roll backward would be a plus.

John
John in CR
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### Re: Linear drive for hulled recumbents

I found a well documented desingn that looked really interesting for a 4 wheel enclosed pedal vehicle using stepper system!
but i forgot to bookmarck the link

bzhwindtalker
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### Re: Linear drive for hulled recumbents

hum I thougth it used a stepper but I was wrong
http://poisson.jp.free.fr/zebulon2/index1.html

bzhwindtalker
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### Re: Linear drive for hulled recumbents

bzhwindtalker wrote:hum I thougth it used a stepper but I was wrong
http://poisson.jp.free.fr/zebulon2/index1.html

Very fishy
The design could benefit from a linear drive but he could also build it with a steering tail.
I like the carbon fibre chassis. In my neighborhood we have an aircraft repair service. I'm tempted to pay them a visit, especially their garbage could contain some useful fibres
-Olaf
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### Re: Linear drive for hulled recumbents

John in CR wrote:A a single rowing bike with a fairing should be able to break the 81mph HPV world record, since you could transfer so much more power to the wheels than pedal alone via legs, back, and arm muscles, just like rowing. Once you make it a tandem, it should be able to slaughter the record by a wide margin, since you gain almost no additional wind resistance but double the power and can make the power transfer continuous instead of discontinuous. I'll leave coming up with that kind of thing to you cyclist guys. In the meantime, I just want to break the HPV record using an electric motor, which should be a matter of simplicity. I also have a both a current bike build as well as the next one in line where I see a linear stroke as great benefit in terms of space and comfort.

An electro magnetic toothed clutch/brake as the clutch for this mechanism to allow reverse might be ideal. Then unpowered would be engaged, and in those rare events you need to roll backward it uses a bit of juice. I can foresee instances, like stopped or parked on an uphill, where the inability to roll backward would be a plus.

John

I doubt that a rowing bike would be any faster, as the human body power limit at present is aerobic. Using more muscles groups does increase the initial power available, but the body will quickly go into oxygen deficit because the lungs won't keep up with the muscle oxygen requirement. It's a bit like the analogue of a big motor and controller with a small battery. At first the motor will deliver loads more power, but the battery will soon give out. Our legs alone at full power can overcome the ability of our lungs to provide adequate levels of oxygenated blood, probably because we evolved to be pretty good at running.

I like the idea of the reversing clutch, it could be something as simple as a mechanical lock released by a cable, operated in a similar way to the gear shift in a hub gear.

Jeremy
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### Re: Linear drive for hulled recumbents

I have been thinking of a recumbent fairing & this is a nice option. My original thought was simple linear bearing guided pedals that would pull on a cable. A cable can route the energy to the clutch/pulley any where that would make the fit better. A lightweight coil spring would provide recoil action. a recumbent stair-climbimg excersize bike

Does any one have the stats on how much cranking energy is generated by cilp-in pedals that allow the rider to use the biceps-femoris muscles?
I imagine the "speed" trial guys use all their leg mucsles....wouldn't effect myself (lazy pedaler)
get some......

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### Re: Linear drive for hulled recumbents

Jeremy Harris wrote:
John in CR wrote:A a single rowing bike with a fairing should be able to break the 81mph HPV world record, since you could transfer so much more power to the wheels than pedal alone via legs, back, and arm muscles, just like rowing. Once you make it a tandem, it should be able to slaughter the record by a wide margin, since you gain almost no additional wind resistance but double the power and can make the power transfer continuous instead of discontinuous. I'll leave coming up with that kind of thing to you cyclist guys. In the meantime, I just want to break the HPV record using an electric motor, which should be a matter of simplicity. I also have a both a current bike build as well as the next one in line where I see a linear stroke as great benefit in terms of space and comfort.

An electro magnetic toothed clutch/brake as the clutch for this mechanism to allow reverse might be ideal. Then unpowered would be engaged, and in those rare events you need to roll backward it uses a bit of juice. I can foresee instances, like stopped or parked on an uphill, where the inability to roll backward would be a plus.

John

I doubt that a rowing bike would be any faster, as the human body power limit at present is aerobic. Using more muscles groups does increase the initial power available, but the body will quickly go into oxygen deficit because the lungs won't keep up with the muscle oxygen requirement. It's a bit like the analogue of a big motor and controller with a small battery. At first the motor will deliver loads more power, but the battery will soon give out. Our legs alone at full power can overcome the ability of our lungs to provide adequate levels of oxygenated blood, probably because we evolved to be pretty good at running...

That makes sense for the how far you can get in an hour HPV record, but I was thinking of the absolute speed record, which is a sprint. I wonder how long it takes before the aerobic limit is dominant.
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### Re: Linear drive for hulled recumbents

John in CR wrote:That makes sense for the how far you can get in an hour HPV record, but I was thinking of the absolute speed record, which is a sprint. I wonder how long it takes before the aerobic limit is dominant.

I'm not sure, but we can get an idea from the way the performance of runners falls off with distance.

100 metres can be run in a bit under 10 seconds (but around 50 to 60 metres of that is acceleration time)
200 metres can be run in a bit under 20 seconds
400 metres can be run in about 43 seconds
800 metres can be run in about 101 seconds

This seems to show that the aerobic limit starts to kick in at around the 35 to 40 second point and is having a major effect by the 100 second point. If you could accelerate a bike with a rowing power system to 80 plus mph (to beat the record) in less than perhaps 35 to 40 seconds, then I guess it would be an advantage. This implies a 0-60 time of around 20 to 25 seconds, so it might be do-able.

Jeremy
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### Re: Linear drive for hulled recumbents

Here's a pic from Miles' Modern Mechanix thread. Levers/freewheels drive from 1937...might be some useful idea in there to add to the mix

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### Re: Linear drive for hulled recumbents

Yet another reason for alternative drive types is reducing joint load. Taking even 30% of the load directly from hip/leg motion above the knee can greatly reduce joint stress.
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