Design Problem – what we’re fixing & why it matters
Kenya’s dry-season landscapes lose vast numbers of seedlings to heat, grazing and erosion; hand-planting is slow and labour-intensive, and aerial seeding is too costly for student-scale projects. Our goal is to build an inexpensive, vehicle-mounted seed-ball launcher that can ride on a Rhino-Charge-style 4×4, flinging clay-coated seeds rapidly and accurately into hard-to-reach ground. The opportunity is two-fold: (1) give conservation teams a light, modular tool that can be bolted onto any off-road vehicle and (2) prove that high-speed fly-wheel technology, normally seen in hobby robotics, can be repurposed for ecological restoration at almost zero consumable cost. Because seed-balls already contain clay, compost and local grass/tree seed, every shot is a micro-habitat that protects the seed until the rains arrive – multiplying the impact of each field trip.
Design Problem – what we’re fixing & why it matters
- Ideation & research – We brainstormed six dispersion concepts (RC plane drops, air-pressure cannon, tea-bag seeds, etc.) and chose a dual-fly-wheel “Rhino-Charge car dispersion” concept for its simplicity, adjustability and on-road power supply. Initial inspiration boards and sketches live on the Research/Design Ideas page.
- Rapid prototype (Lego EV3) – To prove the physics we built a handheld EV3 rig: two Lego wheels spun by Lego large motors, tensioned with rubber bands to boost grip. This let us see that soft tyres could bite and accelerate 35 mm clay balls without shredding them.
- Motor & power selection – Small toy motors stalled, so we sourced 12 V 18 000 rpm brushed DC motors and wired them in series to keep current under 3 A; a Li-ion drill battery gives field portability. Bench tests confirmed opposite polarity makes the wheels counter-rotate, straightening the launch.
- Custom wheel rims (five CAD iterations) – Standard Lego rims wobbled, so we modelled a press-fit rim in Tinkercad, 3-printed it, discovered tolerance, stringing and warping issues, and iterated four more times in Fusion 360: enlarging the bore, sinking screw holes, and re-centering cut-outs until the motor sat flush and balanced. The final “V5” rim was printed in PLA+, hot-glued to the motor shaft and balanced with tape.
- Feeding mechanism – Time pressure led us to a gravity hopper: a 1 inch PVC pipe cut in half forms a slick ramp that drops one seed-ball at a time between the wheels. Later sketches explore an agitated hopper for continuous feed.
- Speed test & validation – Using 15 cm stripes on cardboard and 240 fps slow-mo video we clocked exit velocity at ~146 km h-¹. Frame parallax and board flex add ±10 % error, but the test confirmed we easily exceed the 20 m range needed for roadside seeding.
- Next steps –
- Re-print tyres in flexible TPU for higher friction and less expansion.
- Integrate an Arduino-based RPM sensor and PWM motor controller for repeatable range settings.
- Design a spring-loaded gate to meter seed-balls and prevent jams.
Short demo clips (linked on the “How it Works & Videos” page) show the EV3 prototype spinning, the first PLA rims at full throttle, and a slowed-down launch. Feel free to embed any of those .MOV files beside this text to illustrate each stage.
Link to Process Journal and Final Reflection Video
https://sites.google.com/isk.ac.ke/cass-stem-impact-project-semes/home
https://app.screencastify.com/v2/watch/yE9qEj2Y02QNuSJmBU6X
