Hey, I’m making a project for school and it would be great if someone could point me to a diagram or a visual of what exactly is happening when the motors apply resistance in brake mode. Thank you 
Grab both all the power wires coming off of the motor. Connect the bare ends of the wires all together.
The other thing you need to know is that motors, when the shaft is driven instead of the wires, act like generators. The power generated powers the windings going the other way.
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Wait I just realized you weren’t joking 
Not in the slightest. The motor controller does that when it’s put into brake mode.
It’s slightly different in exactly how it does it between brushed and brushless motors–mainly because they’re set up differently–but as long as that wire connection is joined together, the motor tries to stop itself.
Coast mode leaves the wires not connected together, BTW.
You may want to ask @jdao or @Wishbonea about setting up a practical demonstration with some of the CIMs in y’all’s shop sometime.
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One caveat between brushless and brushed motors in terms of braking is how the motors are driven. When you short both wires coming out of a brushed motor there is nowhere for the energy to go except back into itself so any movement is essentially canceled out.
On a brushless motor it is driven by applying power in very short bursts at 3 points essentially pushing the rotor towards the next pushing point. If you only short out two of 3 the third can still push potentially and be a pathway for energy in and out.
In FRC we don’t worry about the amount of braking energy being generated, we just dump it back into the battery. Our overall weight (amount of power needed to brake something
in motion) and power (12v limited amperage) make this feasible.
As you scale up you will start to find stuff like brake resistors or clamping devices like this ODrive Regen Clamp – ODrive Robotics to divert excess energy away from the battery and dump it out elsewhere. These brake resistors can get very very hot. It’s okay to let energy go back to a battery, but not in excessive amounts.
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I did a lot of testing with a NEO a while back looking at all four quadrants of operation and braking mode. Lots of gleefully over the top and janky testing! Neo braking mode information - #2 by Weldingrod1
When the motor is commanded to be at zero speed, brake mode is 100% shorted wires as discussed above. In fact, its better than two shorted wires! You must have all three shorted to simulate what a spark max is doing! I tested this too…
The situation is different when the motor is being told to drive at a speed and the shaft is doing something different from the command. This often happens when the robot is running fast and then is told to slow down/stop. In this case the way the three phase bridge works means the voltage generated by the motor is rectified back into the battery.
Also worth knowing, the current limit on a sparkmax doesn’t work right in the overhauling quadrants; where the torque direction and the commanded direction don’t match. It DOES work right in the two normal quadrants.
Brake mode continues to work when the robot is disabled.
Brake mode does NOT work when the robot is turned off.