Look at the design page for info on the plywood velomobile construction.

Saturday, 14 January 2012

Lineair drive

The conventional pedal rotates around the crank axle. In a velomobile with rotating pedals the feet are not only moving in driving direction but also up and down. Should the up and downwards motion be done away with the nose of the velomobile could be much lower. That may improve the aerodynamics of the body.

multi body of a human leg
Instead of a rotating crank we could use an oscillating crank. The pedals would move for and backwards while the crank rotates 60ยบ only. The cranks could be connected via 2 sprag clutches to the wheels. But than the pedal speed would be almost constant. Only at both extreme positions the pedal speed would have to change very fast to the opposite direction. Is that comfortable and efficient?
motion of center of gravity of thigh, calf and foot [m]
To get an impression about the losses that could be created I calculated the kinetic energy of the thigh, calf and feet of a human leg while driving the lineair drive. At the returning positions they are 2 and 5 Joule. The last value is when the leg is stretched. Humans (animals too) are able to optimize their motion. It could be that we would stretch out our foot in the last phase to reach the most stretched leg position. In that case the kinetic energy of the thigh and calf would be recuperated. I think this is what we do while we are running.
kinetic energies Et: translation, Er: rotation
But in the most pessimistic approach all kinetic energy would get lost: 7 Joule at every stroke. At a normal frequency of 1.5 Hz that would amount up to 2*7*1.5=21 Watt. That is an enormous  amount. A normal bicyclist produces 75 to 150 Watt! It may be that the foot motion has to be decelerated and accelerated in a controlled way at the returns. This kind of loss may exist in the rowing bike too. Is there anyone out there who has done experiments with lineair drives? Paul Jaray developed a similar drive in 1920. Miles Kingbury developed an interesting alternative: the K-drive. The Human Power-team is experimenting with it too.


  1. Hi Titus,
    Theo van Andel experimented with a kind of K-drive. For touring perfectly suitable, for racing not. It proved to be impossible to reach high pedal rotations. He is now experimenting with short cranks.
    Best regards,
    Wim Schermer

  2. 30 years ago I did a quick and dirty test of a linear drive. We made a sort of recumbent home trainer with two flywheels. The wheels were bicycle wheels loaded with lots of lead to simulate the inertia of a hpv. They rotated around vertical axles. Two vertical beams of ~1.5 m were hinged to the floor. At the top of the beams a chain was connected to the freewheels of both wheels. We put our feet at ~0.4 m from the floor on the beams and could drive both wheels one wheel for each direction. It felt very ok. But no information about efficiency... Meindert Valenteyn (touwtje fiets) Derk Thijs (roei fiets) and Paul Jaray (J-Rad) use and used the same principle.

    1. Did you read what HPT Delft is doing?
      Jan Bos is traning with these cranks.

  3. No I didn't ! Thank you for your tip.

  4. Linear Drivetrains do work. i note- the same old problem.
    a bicycle crank will allways have a dead spot top-n-bottom of the Stroke.
    the best system is to reciprocate the sweet spot of maximum torque. useing non standard parts.
    at a wide radius 40cm giveing a full Pedal power Stroke of 30cm. here's how..
    two independant swinging Pedals gives the rider a choice of rowing , over-lap or recuperateing Strokes.
    Pedals must have long 40cm arms. can be ether way round Pedals-top=pivot-bottom.or Pedals-bottom=pivot-top as here-
    use a chain loop or noose on the Pedal arms with sprockets top-n-bottom. one side of arme.
    top sprockets are an idlers & can be 10 or 18 tooth. use wider industrial chain as bicycle chain is too narrow
    in useing ( 8 tooth sprockets ) at pivot bottom are used to change Gears. the chain loop is a Y with the drive cable pulling
    the third side of the triangle. moveing drive cable up or down the radius. other end to the wheel hub then to the
    long & light Return springs. -pedal Return springs Only work IF there long & light. 35cm stretching up to 65cm.
    { light springs } no more force then the energy used to lift the oppoing foot. on a rotating bicycle crank.
    by adding Kick-up pulleys at the end of the Pedal Stroke makeing contact with the loop pulling it in-& UP to add more
    pull on the drive cable slows the Pedals to a stop. but adds energy to the trike/bike. the chain loop is for changeing
    Gears by way of the bottom two L& R hardened steel 8 tooth sprockets/axle-pivot. just rotate & lock.
    why use 8 tooth? to keep radius creep-up low as you can in the Gears . drive cable/or chain gos to the wheel with two
    one-way clutches on the sides of the hub . Friction is not a problem if you use all ball bearings on idlers no sleeves.
    prove the concept ! it will work . note- the Pedal arms must be strong.( torque or twisting is much higher then
    a bicycle crank.) it works! just ditch the use of standard bicycle parts! have fun JONOVID