Geared v.s. Direct Drive eBike motors
Posted by Tom Lee on
We often get asked what is the difference between geared motors and direct drive motors?
From the outside of a motor, you can’t see much difference between the two, however inside there is a huge difference.
Geared motors
Geared motors have an epicyclic gearbox inside the motor casing, which has an outer gear with inner teeth which connects to the wheel, 3 planetery gears, and then an inner gear connected to the motor itself.
It looks like the photo above.
The reason for making a motor like this is that you can have the motor coils inside spinning at a higher rate than the wheel on the outside. Motors generally work better when they are spinning faster, and so this means you get more bang for your buck when you accelerate with one of these motors.
Generally we prefer geared motors as they are more efficient – they also come with a built in freewheel which means that when you spin the wheel forwards, the motor inside doesn’t move. This means you can use the bike like normal for cycling when the power is off.
A nuance of this freewheel is if you connect the controller the wrong way and it spins the motor backwards, the wheel won’t move… so if you hear the motor spinning but nothing is moving then swap two of the motor phase wires around and try again.
Another nuance of this freewheel is that it does engage when you spin the motor backwards, so if you want to for instance measure the voltage coming back on the motor phases (to check for shorts) then you should spin the motor backwards.
Direct drive motors
However, to get the gears inside you have to use a lot of space, and this sacrifices potential torque that you could get by filling that space with more motor windings and or magnets. Therefore some higher power motors do not have the inner gearing, and the motor inside spins at the same speed as the outer casing and the wheel.
There is no freewheel in direct drive motor, and that means if you spin the wheel, the motor spins too, whatever direction. Because there are magnets inside the motor, this creates drag as the motor spins past these magnets, the result is if you don’t connect controller power you’ll get drag when cycling
The upshot of this drag caused by direct drive is you can make use of it to do regenerative braking. Instead of using friction to brake, you can use the resistance of the motor to suck energy out and stop the wheel, sending teh power back to your battery. This requires clever power electronics and in general is not worth it unless you are tackling lots of hills. See our upcoming blog “Is regen braking worth it?”
So direct drive and geared motors each have their advantages, but overall we massively prefer geared motors. That’s why most of our kits use geared motor wheels.
