It has been a few weeks of browsing through my den of broken things to put together a test rig. The reason being to please my self doubt about what I am trying to do. A lot of times I have questions floating in my head if I could actually pull this off. I have been messing around on the internet and trying to find something that could show that my half baked ideas is actually worth the time. Time is on my side. I have stopped working for the moment. I ended my previous job as a Manager for Fire and Gas Detection system with Draeger Safety with a small compensation package. That bit of kit would probably last me a few months before I actually need to find a job. At 45 years of age, that is not going to be easy.
I have taken a piece of wood from my hoardings and bought a cheap set of planer. The last time I used this was in Secondary School in the early 80’s where we learned woodworking. I therefore whittled down this piece of wood for two days to come as close as possible to the profile that I needed. I also used my dremel and coarse grit sandpaper to give a good smooth finish. Woodworking is very addictive I must say. I find myself constantly reshaping the profile untul it looked satisfying to my eyes. I was not looking for an effective aerodynamic profile. I wanted it to look good. I had to force myself to stop because I needed to do this rig and reassure myself.
I took the finished piece of wood and proceeded to find the center of gravity. This is crucial as this would help to reduce the torque demand on the servo motor. Placing the servo in line with the axis of rotation means reducing the weight that had to be moved around the axis. I simply held the spoiler by the side of both hands. I slide both hands to the center of the piece. Where the tilted, the weight has gone the other way. I slid the hand which had no resistance because of this shift. I put the wood on a pen and tried to balance it as much as possible. This way, I found the center of gravity and marked with a pen. I then used the grain of the wood to show me the pivot point at each end of the piece.
Then I looked inside the cabin again to find unused TV stands meant for my 42 in plasma TV. I drilled both at an approximate height. The undriven pivot side was held by a simple screw. The driven side had a servo hub which was nailed. The hub has a 24T spline which would normally be attached to the servo shaft and screwed in place. This is another issue that I would need to address. I would need to cut an approximate width of 20mm to enable the screw to tighten the sawn wooden piece against the servo. Once that servo is tightened, it would then be screwed to the main piece.
I have been trawling the pages of Servo City for a few weeks now and have ordered some bits and pieces. I will tell why I need those a few paragraphs later. I have made a test rig to show myself that the small servo could turn the wooden spoiler. A video of which can be found on my facebook link here
What I have realized after playing with the test rig is that the weak link lies in the connection to the HITEC Servo. This HITEC HS 425BB was bought from a local Arduino authorised agent at MyDuino.com. It was the biggest RC Servo that they had. I could see that at a speed of 200km/h and with a surface area of 7,500mm2, the wind load on the spoiler would only be contained by the servo hub and the swivel joint. Even though this HS 425BB is a model with bearings, I would think that it would not be sufficient to handle the load. Therefore I decided a redesign is in order. Part of the items I hard ordered online was an aluminium arm to connect to the spoiler. But because the spoiler would have a different pivot point and than the servo, the hole on the arm must be modified to a slot.
Having two support on the driven side would increase load capability. This also means is that the torque demand on the servo would be increased. I am prepared to make the spoiler lighter by hollowing; making more holes where necessary.