As per title, an electric assist system for your bike, but it's all in the pedals which can just be swapped with your normal ones. Can't quite see how this is supposed to work- could it?

Wired electric pedals

And according to the article he's a finalist in a Barclays business competition.

That's not the same thing though…

Presumably, the motor drives the shaft to help rotate the crank arm around. It seems to work (in my head) in theory, but I reckon it would feel somewhat odd. And they look flipping heavy pedals!

eh i dont get it ? surely the pedals will try to 'tilt upwards' all the time abit like 'reving' a motorbike. this will feel rather strange…
and retail at 200 quid…. nicer things to spend that on..

So, ignoring what the twisty turny torquy stuff works against, have a look at the energy involved…

Li-poly batteries have an energy denisity of around 350Wh/L (from PowerStream)

This is 1260000 joules/litre

Looking at two typical pedals with a length of 10 cm, a depth of 2cm, and the battery width of 1cm, then the volume will be 4 x 10 x 2 x 1 = 80cm, this 80/1000 = 0.08l.

This gives us 1260000 x 0.08 = 100800 joules.

Given E = mgh, this re-arranges to h = E/mg (sorry, edit).

g ~ 10 (ie that rounded up 9.81 from school) and mass of bike & rider = 100kg.

So the batteries (100% efficiency all round), would lift you up 100 metres.

So in the real world you would be paying £200 to lift you through ~50m (50% efficiency) around 300 times (recharge cycles of Lithium batteries).

Bargain …..

Think I've got how this is supposed to work now, but wouldn't the rider have to oppose the rotation of the pedals and so do more work?

have to oppose the rotation of the pedals and so do more work?

Precisely, the pedal effictively becomes a motor where the shaft is fixed to the crank. If it's got sufficient power to make a difference, it could feel quite funny to use, balancing the normal pedalling forces and reacting the 'motor' forces….

More to the point, wouldn't the pedals unscrew themselves from the crank?

I guess, provided the pre-load torque to fit the pedal is greater than the torque the motor can generate, then you're ok. The prototype shows the shaft drilled for a torque pin (and non threads!), so it probably needs a bit more work to use with normal cranks.

Still don't see the gain, if to keep the pedal from spinning you have to do the same amount of work as the motor.

Hi MrSalmon,
You don't do work without movement. Power = force x velocity. The rotational velocity of your feet is effectively zero, so you don't do any "work". The pedal does the work by rotatig the crank. All your foot does is act as a fixed torque arm – which must indeed feel strange.

Waste of time.

Hi MrSalmon,
You don't do work without movement. Power = force x velocity. The rotational velocity of your feet is effectively zero, so you don't do any "work".

Er, right. My Physics degree is starting to seem like a long time ago 😳