Lightning Bug
The Invention
Lightning Bug is an electric-powered alternative to the Briggs & Stratton LO206 gas-fueled motor commonly used in competitive kart racing.
It is born from our many discussions about what would make a great electric race-kart engine. Goals include overcoming the evident and subtle issues in electric karts and currently available conversion kits.
The apparent issues include the price: of $3000 to $5000 for an electric conversion kit and the downside of making permanent kart modifications like drilling and welding.
The subtle issues are related to changing the center of mass when swapping a gas motor for an electric one and its batteries.
The Process of Invention
Vision and Research
- Brainstorm ideas that were refined into testable requirements and goals
- Calculate power requirements, determine approximate motor and battery specifications
- Research motors and batteries to validate the concept was viable with existing off-the-shelf products
- Determine battery type: swapping batteries charged overnight was faster, less expensive, and easier on race day than using a quick-charging battery system
Design and Build
- Finalize high-level design, created bill of materials, ordered parts
- Bench-test the motor controller to verify and document the wiring schematic
- The throttle control test failed: the motor controller expected a hall effect sensor, not the variable resistor in the cable-actuated throttle position sensor we ordered
- Design and build a resistor network to embed in the throttle position sensor to emulate the hall effect sensor output voltages
- Design and machine adapters for the front drive sprocket
- Final assembly and bench test
Test and Race
- Install on the kart and live test on the stand
- Take to the track and test on the ground
- Race on the track alongside LO206-powered karts without any failures or issues
Success!
Lightning Bug successfully met every requirement and goal:
Durable and safe for recreational and competition use
'Bolts only' conversion for existing race karts
Great on-track performance
Each battery powers two races per charge and take less than 60 seconds to swap
It was built from readily available motors, batteries, and other parts
The retail cost to build (including two batteries) is less than $950 (a race-ready LO206 is around $1250)
Details
Safety Design Features
- Integral chain guard
- Emergency kill switch
- Main circuit breaker
- Battery enclosure cage
- No exposed connections
Battery Life
- Two 15-minute races per battery
- Battery swap faster than refilling gas tank; 60 - 90 seconds
"Bolts Only" Conversion
- No frame modifications or set-up changes needed
- Bolt pattern: identical to LO206
- Form factor: similar size, shape, and weight
- It uses the kart's existing throttle cable, gears, and drive chain
Weight and Center of Gravity
- Lightning Bug weighs 52 lbs with a battery
- LO206 weighs 51 to 57 lbs with fuel and oil
- Center of Gravity moves less than 2% with a Lightning Bug conversion
Power, Torque, and RPM
- Power: Lightning Bug = 3000 Watts (4.02 HP)
- Power: LO206 = 8.2 HP
- Torque: Lightning Bug = 4.43 ft-lbs at all RPMs
- Torque: LO206 = 10 ft-lbs @ 3000 RPM
- Max RPM: Lightning Bug = 6500 RPM
- Max RPM: LO206 = 6100 RPM
Testing Parameters
- The track layout, kart, tires, alignment, weight, and driver were all the same.
- The fastest and average lap times for the Lightning Bug and LO206 are within +/- 3%
Cost
- Lightning Bug prototype (with two batteries) - $950
- LO206 complete engine package - $1250
Next Steps:
Fully refine Lightning Bug into a commercially viable product.
Manufacture and sell, or license the design and name.
Freely distribute DIY plans to stimulate the growth of electric-powered karting further.
Promote industry adoption through sponsorship of local racers.
Apply to have Lightning Bug sanctioned as a kart engine classification.