ScorpionKing wrote:I am also exploring whether or not I really need an E-Brake on my Trike. This is my first build and I am using a Mac 10T geared hub motor. I have oversized hydraulic Shimano brakes and rotors up front on my tadpole Trike and I am used to stopping at higher speeds. So I wonder if I really need a switch.
V's post above goes directly to this question. Important stuff.
Voltron wrote:But re. cutoff brakes or a bar mounted cutoff switch in general, don't forget they are there for when things go wrong and the motor suddenly jumps to full power from a shorted throttle or something... it's not just for normal stopping, it's your emergency safety override.
There are different schools of thought here - I'm belong to the "it's gotta have a kill switch" faction. This covers more failure cases than relying on ebrakes alone and doesn't suffer the problems of integrating a switching mechanism into brake levers. Opening this connection shuts off processor power so the controller simply goes dead regardless of what failure has occurred.
Controllers generally have a power or 'ignition' wire. Just run this up to the bars with a toggle or latching switch and you're done. The voltage is high but the current is low so arcing is not much of an issue. Since this is something you're going to want to hit in an emergency, ideally you want the switch reachable by thumb without releasing the grip - to which you will likely be clinging for dear life.
My first bike didn't have PAS for a couple of years and so I rode without ebrakes with no issue, relying for safety on the kill switch. The ebrakes were a retrofit that came with adding PAS. The next bike was designed from the outset with PAS but got a kill switch as a matter of course. Here's a kill switch using a toggle mounted on a Magura throttle with a bit of aluminum scrap. The switch is positioned to be aligned with the thumb after zeroing the throttle (presumably to no avail).
- To put runaway failure modes in focus:
Although shorts of exactly the proper throttle wires are unlikely, faulty connections due to loose pins, vibration, or corrosion are not. The most common runaway cause is simply losing the throttle GND connection. This allows the throttle +5v wire to immediately pull the throttle signal wire up to 5V with an accompanying wide open throttle response from the controller. This particular failure mode is why many controllers have a 'throttle fault' feature that shuts down the controller if the throttle signal exceeds the 'usual' throttle max of about 4V - if your controller has the feature, enable it.