Hub - Direct Drive
Direct drive hubmotors spin the wheel without any gears or sprockets, so they are geared 1 to 1.
One revolution of the motor is one revolution of the wheel rim. This means the motor must be designed for a relatively slow rpm compared to most electric motors you are familiar with, like a drill or a car starter.
To improve torque, a direct drive motor is often a pretty big diameter, dinner plate size is common.
A direct drive motor is always either using power or making power if it is spinning. So a direct drive motor can be used with a regen enabled controller to recharge the battery while coasting, brakeing, or just pedaling with the motor off. The efficiency is low, so pedaling to charge the battery is not very effective. Regen braking can be a great way to improve braking, and reduce wear on mechanical brakes, even if it never puts large amounts of power back into the battery.
When pedaling a bike with a direct drive motor that has the power off, the motor will resist some since it is trying to make regen power. This happens even if the controller cannot do regen braking. This resistance can be a good reason to choose a gearmotor that has an internal freewheel that allows coasting without regen resistance. But if you still have power left in the battery, you can make the resistance go away with a very light touch of throttle. At just a trickle of power, you can pedal freely without losing much battery power and still pedal to extend range with a direct drive motor.
Most common direct drive motor failures
Most direct drive hubmotor failures happen in one of two ways. Overheating the motor, or cutting the wires at the axle. Most repairs involve removing the hub motor covers. The best method is to use a large gear puller. Remove the cover screws, and use the puller to push on the axle, so the cover on the opposite side pops off. You may want to remove the entire stator in the process. Once the core of the motor is pushed entirely out, you can use the puller to pull the remaining cover off. When replacing the stator, the magnets will snap the motor core into the wheel VERY HARD. Handle the core by the axle, so you don't get a finger snipped off. Melted motors. Three things can be wrong, burnt hall sensors, shorted phases, or melted solder disconnecting wires. Shorted phases. The phase wires are the large size wires to the motor, usually blue green and yellow. Unplug the motor from the controller. Turn the motor by hand, if it resists more than it used to, you have shorted the phase wiring in the windings, unless you have a short at cut wires, or melted wire insulation. To simiulate what a shorted phase feels like, after you unplug from the controller, connect two phase wires to each other. The motor will now resist hard. No easy fix for shorted windings, the fix is rewind the motor. Melted solder. Occasionaly an overheated motor may only need a wire re connected. Solder melts, and disconnects a wire. Burned hall sensors. The hall sensors are connected to the smaller red,black,blue,green and yellow wires. To test a hall sensor, connect a 5v battery to the red + and black - wires. Connect a voltmeter to the red wire, and one of the B G Y wires. As you spin the motor the voltmeter will show the hall sensor turning on and off, if it is good. If the motor is already taken apart, wave a small magent over the hall sensor to see if it will toggle on and off. Replacing hall sensors is fairly easy, but some soldering skill is reqired because the hall sensors are tiny. If you have not remembered to take notes, solder the wires like this. With the sensor facing up, so you can read the printing on it, Red on the left, black on the middle, and on the right, green blue or red. Cut wires. This tends to happen when a motor axle is not held completely still in the dropout. With out a torque controll device such as a torque arm, the motor will spin the axle if enough power is applied. This can nick a wire allowing it to short or ground. Shorted phase wires can blow a controller. The fix is to replace the wires, splicing them is not practical because the cut is right at the axle. It can be possible to pull more wire into the hub, and make the splice to repair a cut wire inside the motor.