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cars:motor_controllers

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Motor Controllers

There are generally two types of motor controllers, which must match your type of motor:

  • Brushless
  • Brushed

Since most existing karts and all recommended new builds contain Brushless (BLDC) motors, this wiki will focus on Brushless Motor Controllers.

In addition, the speed controller will have specifications you must work within to prevent failure:

  • Voltage - make sure the controller operates within you max/min voltage
  • Current - make sure your controller can reliably control the amperage of your motor and batteries
  • Throttle - some controllers accept 0-5v for throttle input (often called a “hall effect throttle”); some require 0-5k ohm potentiometer input, some will accept either.

The motor you use will have to be selected in concert with the controller that will operate that type of motor. In order to comply with the rules (1.9) you are required to use a throttle-controlled motor controller, such that your control over the behavior of the motor is continuously-variable. your controller may come stock with a thumb or twist style throttle for mounting on a handlebar grip, or you may have to buy a throttle separately. A foot pedal is an acceptable throttle.

Wikipedia has more information on the topic of electronic speed control.

Different speed controls have different features to be aware of:

  • Variable speed
  • Electronic braking (or even regenerative braking)
  • Direction control (forward / reverse)
  • Acceleration control
  • Current control / amp limiter

Your options for obtaining your speed control are:

  • New - lower power controllers can be had for cheap; high powered get very expensive very fast
  • Used - Often a good choice for higher power controllers, if you can find a deal
  • Build-your-own - Can be very inexpensive for lots of power, but obviously much more complicated.

New

The Internet has many new, very inexpensive controllers floating around, in both brushed an brushless forms. They are generally designed for usage in scooters or e-bikes. These type of controllers go by many colloquial names within the league: “ebay special” “chinese special” “slow boat from aliexpress”, but they all generally refer to the same category of BLDC controller. they are non-programmable and

  • this family of controllers has:
    • low-current e-stop wire pinned out that must be tied high for the controller to be enabled. (usually red in color)
    • reverse input (often brown in color)
    • top speed cut-off selector (typically does not change acceleration curve) also translated as “three speeds” usually, unconnected is “medium” speed, and shorting the correct wire to the black wire will set the controller to “fast” speed, increasing your motor top RPM.
    • typically accepts only hall (not resistive) style throttles

Sources:

Spicing up the Ebay Special

A regularly used technique in the league is to purchase one of these Ebay Special controllers rated for 48/60V and 1500/2000W and modifying the internals of the controller to “make it spicier”. Teams often colloquially call this process “spicing” the controller. The general process is:

  • Take the controller to bits. screws along one side will unbolt the heat-sink block of aluminum from the housing, and the screws on the end-cap with the wiring harness sticking out of it will allow the PCB/endcap/internal heat sink assembly to slide out of the housing so you have access to the board.
  • Identify the portion of the PCB which is the Current Monitoring Shunt. The Shunt is usually on the Low Voltage side of the main bus (nearby to where the large black-insulated wire terminates onto the board) and is comprised of one or many solid core wires which are the only connection between the low-voltage trace out of the MOSFETS and the trace the large black wire terminates.
    • The way these controllers limit their flow to the stickered current draw (32A? 34A? whatever it says) is that the internal microcontroller measures the voltage drop across this shunt and calculates the flow of current through the controller based on the measured voltage before and after the shunt, and continuously modifying the flow of electricity based on this measured feedback. If you change the resistance of this shunt, it will in turn change how much current the controller will allow through. more resistance: less current (this is never desirable in the league) less resistance: more current. (this is the goal of this process)
  • Glob liquid solder onto the shunt, to decrease the resistance across this shunt. the additional solder (spice) applied to the shunt “tricks” the controller in to allowing more current through the controller.

It may take a couple of tries to get the correct amount of spice applied to your shunt. too little, and the controller won't provide much “get up and go” – it'll just feel sluggish. too much, and you risk blowing your regulation fuse nearly immediately.

Used

It is certainly possible to get a high quality / reprogrammable controller used for much less money than new. Some folks have gotten controllers at scrap metal prices, which is hard to beat. Good sources for controllers include electric fork lifts, pallet jacks, and golf carts.

Name Brands of controller that have been used in the league before: Kelly Curtis VESC

Sources:

if you are efficient with your BOM you may even be able to afford to include one of these at full price.

Build-your-own

Building your own controller can be a rewarding process, but certainly involves more complexity.

There has not been a homemade controller in the league since 2020. make this wiki entry obsolete (or update it!) when you design a controller for your new build and tell us all about it!

There are some closed and open source motor controller projects out there to help get you inspired:

cars/motor_controllers.txt · Last modified: 2025/02/14 09:47 by Nedra