Throttle tune

Throttle Tune – Throttle Adapter for BLDC Motor Controllers

A microcontroller-based board with a PWM-based analog output (RC filter + buffer) to emulate a DAC. The goal is to improve throttle response and add configurable driving modes to cheap BLDC motor controllers (e.g. 3000 W BLDC "go-kart kit" controllers).

Currently it is used in the electric Kettcar conversion with a 3000 W BLDC drive, this board fixes the controller’s unusable throttle mapping and makes the vehicle smooth and controllable adding a lot of flexibility.

Control box with the custom pcb connected between throttle and motor controller
Contains: PCB, key switch, battery indicator, several UI switches

Problem

Cheap BLDC controllers (such as KT-style 3000 W kits) have several issues:

• No configuration options at all
• Speed levels provided by the controller are usually defined poorly
• Only ~2 cm (~60 %) of gas pedal travel is actually used
• Jerky, hard-to-control acceleration (tiny pedal movements cause extreme changes in power - positive feedback when accelerating thus pressing the pedal more makes this even worse)

Using only the original setup makes smooth low-speed driving or child-friendly operation nearly impossible

Solution

The Throttle Tune board sits between the analog throttle pedal (or handle) and the motor controller.
It rescales, filters, and manipulates the signal (fading, modes...) while adding safety and convenience features.

Features

Firmware

• Throttle remap: use full pedal range (configure in/out ranges)
• Ramp-up / fade: prevents stuttering, smoother control (configurable max rate of change)
• Speed modes: 3 levels + hidden "Sport" mode (highly configurable - several parameters on per-mode-basis)
• Reverse scaling: reduced throttle in reverse
• Buzzer alerts: startup-, reverse-, mode switch beeps

Hardware

• ATmega8 microcontroller
• Custom DAC output (0–5 V) to motor controller (implementation: PWM output -> lowpass -> buffer)
• CNC-milled single-sided PCB
• Through-hole components (easy to build/repair)
• 3D-printed enclosure
• Inputs: Hall pedal, reverse switch, speed selector
• Outputs: DAC to controller, buzzer

Hardware

Schematic

pcb_throttle-tune/export/schematic.pdf

Layout

PCB Photo

Example Applications

Electric Kettcar

Documentation: pfusch.zone/electric-kettcar

Wiring of PCB between pedal and controller (right) and the finished vehicle (left).

Electric Lawn Tractor (temporary use-case)

Documentation: pfusch.zone/electric-lawn-tractor

Throttle Tune board inside in box on top of the motor controller, battery powered (earlier project - initial but temporary use).

Repository Content

• pcb_throttle-tune/ – KiCad project, schematic, layout exports
• fw_throttle-tune/ – AVR firmware (ATmega8)
• doc/images – photos of the build and control box

Usage

Wiring

See pcb_throttle-tune/export/layout.pdf for what needs to be connected to which terminals.

Adjust thresholds

Several config options (macro variables) are defined at the top of main.c (see detailed comments). These include controller start/max voltage, pedal min/max voltage, idle voltage, etc.
To calibrate:

• Wire everything up
• Enable DEBUG_UART_DEBUG_OUTPUT_ENABLED
• Build and flash the firmware
• Connect a USB-UART adapter (header pins next to mcu, TX + GND are enough)
• Play with the throttle and observe the UART logs to determine the values
• Adjust the macros in main.c accordingly, compile, flash, try again

Configure / Adjust modes

Driving modes are selected via 2 GPIO pins, each with its own config in the modeConfigs[] array.
Parameters can be tuned per mode using this struct:

//=============================
//==== Mode configuration =====
//=============================
typedef struct {
    const char *name;
    uint8_t maxPercent;     // percent of max possible speed applied at full throttle
    uint8_t maxPercentReverse;
    uint8_t beepCount;      // count beeped when entering this mode
    uint16_t rampUpStep;    // max duty increment per interval (max 1023)
    uint16_t rampUpIntervalMs; // note: must be larger than cycle time (consider when UART used alot)
    uint8_t pedalAverageWindowSize; // window size of the moving average to smooth pedal input (0 = disabled)
    // Future: pedal averaging, throttle curve, etc.
} kettcarConfig_t;

See comments in main.c and adjust as needed.

Build & Flash

Install Requirements

yay -S avr-gcc avr-libc make

Build

cd fw_throttle-tune/
make

Flash

Connect avr controller using USBASP V2.0 ISP programmer using the 10pin connector on the pcb

cd fw_throttle-tune/
make                # compile firmware first
sudo make upload    # flash to MCU via USBasp

Note: Be sure to recompile before flashing, or you may upload an old build...

TODO (future hardware rev)

• Add TVS diode
• Add buzzer footprint (currently wired to spare pin and implemented in firmware, but not documented in pcb design)
• Drop unused terminals (see notes design)
• Add reverse polarity protection
• Add onboard buck converter to be used with e.g. 72V directly not requiring external converter