In last season we used for the first time aerodynamic parts on our vehicle. It included front, rear wing and diffusor. We planned to make also side wings but we did not manage to produce it. Downforce effect of diffusor was after tests reconsidered and therefore we did not use it for our last races. We used simulations of fluid dynamics both in 2D for choosing of right profile and 3D for final CFD. Both wings changed significantly properties of our car so we will continue in their development.
For season 2014/2015 we have used material 25CrMo4, which has higher both yield point and ultimate tensile strength so our frame is safer than previous ones. It is welded by TIG method with stainless steel filler material and we tried to increase the production precision by means of welding table, CNC bending of main roll hoop and laser cutting of tube ends. Frame has lowered center of gravity and is shorter by almost 8cm. It also ensures a new, better driver position.
With steering wheel we continued in long term development, so the result is one of the best steering wheels among competition teams. We are using concept with display unit inside of steering wheel already for several years. For this season we have decided to use full-colour graphic display. Moreover by overall design we get closer to formula 1 concept with buttons in range of fingers. From mechanical point of view we used complete design process in Siemens NX 9.0 and production process with prepreg carbon fiber moulding. This leaded to use of aluminum mould, which had to be hand polished to high gloss. Final product is a brilliant steering wheel with perfect surface finish together with low weight.
Wishbones from carbon fiber composite
After two years of development we could use wishbones made from carbon fiber wounded tubes. We have tested different types of winding on tubes, together with different methods of joining with aluminum parts and different types of glues. Final solution is a solution with inserts from aluminum inserts glued to carbon fiber wounded tubes. We will continue with development and we are planning tests for quality of glued joint and buckling analysis for our new pushrods.
After decision of changing the car concept to two motor design, we had to find proper gearboxes for right power transmission. With our needs for lowest weight and dimensions we didn´t find any suitable so we had to design our own ones. We made a decision to use a concept of planetary gearbox with three planets. After calculations for right gear ratio from several factors, we decided to choose ratio of 4.43 for season 2015. Gearboxes are produced by EDM method, we have used for the first time and they are developed together with company Schaeffler.
Yaw Rate Control System, Torque Vectoring
We are developing a system of torque redistribution between the driven wheels. The system will process data about the accelerator pedal position, wheel revolutions, steering wheel angle, vehicle angular velocity (yaw rate) and acceleration. It will dynamically redistribute torque between driven wheels periodically at a 100Hz frequency. The logic behind is quite simple. If the yaw rate of the vehicle does not match that of the steering wheel, torque redistribution will occur. Car will be easier to maneuver and more precise to drive on the edge. Sliding the car around corners will be minimized (hand-in-hand with fun 🙂 ).
Launch Control System
Launch control is a subsystem of the traction control system that we have developed. It is a software part of electronic control unit. Its purpose is to control the vehicle acceleration start and help the driver to accelerate without even controlling the accelerator pedal. The problem with the launch is that sensors are not capable of acquiring sufficient amount of data about velocity and thus the traction control algorithm cannot be effectively used. Launch control algorithm is reducing motor power so the speed of the driven wheels does not exceed the limit when wheel slip is occuring as long as the vehicle speed is low. This prevents loss of control which would result in a worse lap time. The maximum tangential velocity of the driven wheels in the event of slip is set to 18km/h and traction control algorithm is used when the vehicle exceeds the speed of 8km/h.
Traction Control System
It is a system that prevents the driven wheels from excessive slippage. In order to transfer the power most effectively towards acceleration, wheels must have a specific slip which is around 12% for dry asphalt. This means that the speed at which the driven wheels are rotating is 12% greater than the speed of car. What the traction control can do is decrease power for driven wheels to match the slip preset by driver for the specific event. It is lowering the torque only if driven wheels are slipping by more than 3% and is recalculated at a 100Hz rate. For dynamic events where cornering ability is crucial, slip border is set to lower levels (5-8%). It helps the driver to have good control over the vehicle in corner exits where throttle is applied. The vehicle is then easier to drive on the edge and more userfriendly.
Electronic differential is a simple torque vectoring model. It is a straight-forward system that uses data about pedal position, steering wheel angle and vehicle velocity to redistribute torque to driven wheels resulting in better maneuverability. It is very similar to mechanical differentials but with much more properties and driver adjustability.
The vehicle data measuring system is based on RF technology because of interference and range. The measuring system transmits all data available on the CAN bus, such as torque, revolutions per minute, speed, state of accumulators, temperature of all systems, position data in 9 degrees of freedom, state of the vehicle and other. The system can monitor up to 400 parameters in real time. It is possible to transfer the data to a computer using the CAN bus. Data consistency control is implemented in the computer.