Rotax 122 €3 RAVE Control Unit

2019

Aim of the project: Create a control unit for the exhaust valve (R.A.V.E.) of a Rotax 122 €3 engine to change the exhaust valve opening RPM.

Description: Changing the exhaust of my motorcycle with one based on the dimensions of a JollyMoto 115, despite having a ported cylinder, with medium-long gear ratios the bike struggled to reach the red-line on the sixth gear, even after various carburetion tests the engine continued to have problems opening the valve in sixth gear and remained stalled at around 8000 RPM.

After trying to disconnect the RAVE solenoid and therefore keeping the valve closed I noticed a significant improvement, from there the idea of trying to open the valve no longer at 7800 RPM but rather at 8500/9000 RPM.

The first idea was to directly control the solenoid through a relay managed by Arduino, however reading the manual it would have been difficult to guarantee the correct current absorption of the solenoid which varied significantly with time, for this reason I decided to have the valve managed by a servo motor which could also open it only partially based on the number of revolutions and at a number of RPM decided by me.

There were many problems encountered, the worst of which was interference caused by the ignition coil positioned right near the valve which caused a significant oscillation of the servomotor, a problem solved with a shield on the coil cable and with a different positioning of the servo motor.

A simple prototype was built and tested, subsequently I also designed a small PCB to place everything in a very small space and make it reliable.

A function that hasn't been implemented but can be easily coded is valve cleaning when the bike is below 2000 RPM by taking the neutral signal from the engine, this function can only be introduced when the gears are not engaged.

Results: Various prototype was built and tested successfully, however the final model was not built as the exhaust problems were fixed with a new engine.

Simple schematics:

Control Unit PCB layout made with KiCad: