Gen2/Implement Reverse Mode

From Unofficial Zero Manual
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Goal
A reverse mode is handy when trying to push the bike rearwards uphill, or in tricky traction conditions.
Sevcon's market primarily consists of forklifts and tractors, so the Sevcon is already set up for reverse operation.
Naturally, a reverse mode is unsafe for motorcycles beyond a very limited speed (5mph, say).

Trikester worked with Harlan to install a reverse mode switch on a 2013 FX.

Note
Recent Zero models (2016? seems IPM-related) have a glitch when reverse mode is configured using the standard Sevcon recommendation.
Zero custom firmware could be interfering, or it could be a custom setting; unclear which yet.
How It Works
The Sevcon controller can be programmed to take a digital/binary input as a reverse mode directive.
The Sevcon as used by Zero has some unused pins; one of the digital inputs will be needed for the extra signal. Use SevCon's DVT software and IXXAT cabling to configure this.
Since Zero programs the Sevcon to operate in torque mode instead of speed mode, the reverse mode allows the throttle to operate like a variable regen that transitions to reverse from 0mph.
The transition to reverse can be configured a bit for some motorcycle-specific safety, but mainly to avoid a jerky transition.
Torque and speed limits can be set separately for reverse operation (40% and 5mph are good to start with).
Control
The enable needs to be dual-throw to turn off the forward input signal and turn on the reverse input signal, so use a DPDT or SPDT switch, or a SPST switch that drives a relay.
A momentary push button switch is better for control safety, since any instability while moving in reverse should be resolvable by letting go of the control.
Any kind of binary switch can be used (toggle, etc), technically, but getting into a stuck reverse situation could be dangerous.
Mounting the switch should account for keeping the wiring protected and secure, and the switch should either be weather-rated or in a protective enclosure.
Mount location should be accessible from the left handlebar but not where it can be accidentally engaged.
Trikester's mount placed it in front of the handle, requiring the index finger to extend to reach it.