Spikes

[Jeff_Rice]

Basically, when you turn a motor with your hands (assuming no worm gears or other stuff gets in the way), you're creating electricity. What the brake function does is create a short circuit for the motor. Thus when you turn the motor, the electricity it generates is used to counter your rotation.

In popular science they write about a conducting plastic, and they talk about using it in this manner for car brakes. (They called them "PlastiBrakes")
Just in case you want to read a further description of this phenomenon.

[greencactus3]

Originally Posted by Billfred

Basically, when you turn a motor with your hands (assuming no worm gears or other stuff gets in the way), you're creating electricity. What the brake function does is create a short circuit for the motor. Thus when you turn the motor, the electricity it generates is used to counter your rotation.

If you want a really simple example, get a Lego motor and some wire. If you put the wire on right, that axle should hold like the Lake Murray Dam.

use a new "old" lego motor. the "new" motors are geared down. and old "old" one like mine... like 10yrs old loses its efficiency so it wont work too well
[edit]nvm. it doesnt matter if its geared or not. just dont backdrive it enuf to damage it.[/edit]

[Al Skierkiewicz]

Osc,
Nice job on the explanation but let me add a few things.
On the wire guage, FIRST rules set wire minimum size. You can go to larger wire but at the sacrifice of weight. As long as the proper fuses and breakers are in place, there is no likelihood of fire.
As to burning wires when they fall across the battery terminals, you have a great example of the dangerous condition that exists with a battery capable of more than 400 amps at full charge. Any metallic object that contact both terminals of the battery (or anything the battery is connected to) will cause 400 amps of current to flow. This could be a ring, watch band or necklace where bodily harm is the result. Fire is also a very good possibility and we don't want fires anywhere FIRST robots or people live. Depending on the device causing the short, (a wrench for example) the metal can weld itself to the battery permanently, and the result could be an explosion. Therefore, (I will say this over and over) all battery terminals must be wrapped in tape or other insulating material AT ALL TIMES! There is no exception to this rule, ever. Secondly, all terminals that are connected to the battery must be insulated as well. i.e. main breaker, breaker panels, all connectors.
On the subject of coast vs. brake. The speed controller is capable of supplying a short across the motor, simply by turning on two sets of FETs. This produces braking in the motor through a condition known as "back EMF". It is not a firm brake but does a nice job slowing the robot down to help it become a more stable platform. This method is much more preferable than leaving the braking pins in on the Bosch transmissions.

Final word, insulate all terminal connected to battery at all times, no exceptions. This includes chargers.
Live safe, work safe always wear safety glasses.

BTW, if anyone has an question that they feel is embarassing to ask in public, please PM me. I want you to get the right answer no matter what.