I can't find any figures on what the expected losses would be on a system like this:
https://revolution-green.com/first-chainless-e-drive-system-bicycles/
so I thought I would give the wisdom of crowds a chance and see what STW thinks.
If there are any electrical engineers who wouldn't mind showing their working as well as their estimates that would be even better.
80% at best. IIRC electric motors and generators are around 90% so two of them in line gives around 80%.
I remember reading that the motor/generator drivetrain in a Toyota hybrid is about 85% efficient. A chain is something like 95-98% efficient when clean.
I fogfot the motor will need gearing - thats another 5-10 % losses
An absolutely terribly idea!
A typical permanent magnet electric machine averages around 93% efficient. Yes, it can get to 97 or 98% efficient, but that's a peak value. Because we need to allow for "gears" is the wheel motor to spin at a different speed to the pedal (crank) motor, we need two 3 phase inverters (frequency converters), and the best ones of those are around 95% efficient on average. So, assuming no energy storage on the dc link, ie you have to pedal all the time, so that's 0.93 x 0.95 x 0.95 x 0.93 which is 79.7% end to end, ignoring mechanical losses. Compared to a chain, that is upwards of 98% efficient, that's a horrible loss. And of course, because both the motor and the generator (and their inverters) must handle peak power, even if they never actually run under that condition for long with a typical rider, the system will be catastrophically heavy, compared to a chain, cassette and derailure that only has to transmit the riders pedalling power (it only transmits mechanical force, it does not convert the energy from state to state, unlike in an electric motor!) and hence can be very light (~1kg even for a heavy set of cheap components)
I fogfot the motor will need gearing
I don't think they need gearing do they? You can apply a steady current to a motor and the air resistance or hill will retard it appropriately.
It might appeal to the city bike types because it'll be completely clean and maintenance free, and the chain can't come off etc however the cost would be far higher than this market probably wants to pay. Might make for a neater e-bike tho.
Gearing from the thousands of rpm an electric motor to the low rpm of a bb or wheel. E bikes all have thius step down gearing - usually two stage.
Maxtorque nails it... I design hybrid electric propulsion systems and even with high end premium efficiency PMAC motors and latest gen inverter tech the loss stack up is prohibitive to do what this suggests.
I am aware of some marine systems that do just this.... Large low rpm diesel engine and generator up front and then directly couple to a motor (AC to AC direct phase connection) but this is done for packaging / positioning and not efficiency in mind.
So around 80%? That's actually better than I thought.
I am aware of some marine systems that do just this
Pretty much all of the latest RN large warships do this don't they? Mostly about being able to put things where you want without worrying about routing driveshafts I thought.