Grelinette wrote:Forhorse wrote:Frankly, how much did the strain gauge cost?
What is its share in the overall cost of the project?
Probably less than 1 €, but the implementation is complicated: it is an electronic element of a few mm2, which sticks to a metal part which deforms under stress. The strain gauge measures the deformation of the support on which it is glued. To measure a force, you therefore need a mechanical assembly with a part which will deform precisely under stress. That explains the price: the gauge costs nothing, but the part on which it is glued is part of a mechanical assembly machined with precision, and therefore expensive. When you pay dearly for a force transducer, what you buy is mechanical engineering, in fact.
> It already exists on your electric bikes which only work
> while pedaling, the motor gives more force if you pedal harder!
On advanced models (Panasonic and Bosch engines for example), yes. In fact in the crankset there is a deformable element, with a strain gauge which measures the deformation and therefore the force. On rotten models, there is just a magnet sensor: you pedal, the engine starts fully. I tested both and the force sensor is really nicer. The other is really binary.
By the way, how much does the car ride? Do the wheel motors have a reduction gear or not?