A day after posting Part 4. I did a calculation using a spreadsheet. I could either stick to my existing HITEC or get a slightly bigger one. There’s a local Arduino reseller that has lots of TowerPro MG945 which has a stall torque rating of 12kg/cm at 6VDC. I am definitely going to buy this. Although the gears are of metal, due to the power that’s required, I prefer Nylon to take in the additional service demand. I would also need to reduce the surface area by 30% while limiting the angle to not more than 30º. As preparation to accept this servo I had to install a 3 wire cable taken from a power cord extension. The length is about 1.3m which is sufficiently long to have the new controller next to the mid console close to the handbrake. I have routed this through holes that were meant for the rear water jet for the wiper and through one for the spoiler mounting. It’s a bit harder than just that, as I had to remove two panels and I had to make sure the cable was not interfering with the rear seat belt mechanism.
While at the same time, I found the bracket for the reverse sensor a bit too big for my liking. I therefore made holes to shave off 20g. It was not planned. Since it was hard to remove these panels, I would not be seeing it for many years to come.
A few more days and I finished my mechanical build of the spoiler and had it fitted on the car yesterday 27 May 2014. I had a spin in it around Putrajaya, in the most decent of 80km/h speed. It did not fell off even though all of the wooden part was held in place by nothing more than Dunlop Contact Adhesive and two screws. I had another spin today at much more livelier speed around the same track and it is still there on the roof. I might add more screws to keep it all sane. I used normal green coloured Garden Wire to secure the angle of attack. I do not want the angle to be too big that it would add drag and load onto the new assembly.
I am happy to report that on the first test, I recorded an 18% fuel consumption reduction. Initially the average at 80km/h is 5.3l/100km. Now it is 4.3l/100km. Tell me again how much that hybrid costs! This is amazing. Previously I could only make 4.0l/100km on a flat straight road. But with this spoiler. I could drive it normally without having to use hyper-milling techniques to get close to that. It goes to show that it does make sense to make the air separation as late as possible. The angle of the spoiler closely matches the angle of the hatch. I cannot be too sure if I had also reduced the wake.
With that I have completed the mechanical build and managed to clean the wet kitchen area of my house clear from tools and debris. This gives much joy to my wife. The next steps will be to finalize the electronics.