Adjustable Spoilers Part 5

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.

Cable Routing for Servo

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.

Reverse Sensor BracketA 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.

Rev1 Front 3/4 view

New Wing

Rev1 Rear 3/4 view

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.

 

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Adjustable Spoilers Part 4

 

I promise that this is going to be longer than a Star Wars trilogy.  Best be likened to a Tolkein.  Much so like Elder Scroll’s: Skyrim the PC Adventure game.  A continuous journey where you pick up little treasures along the way to and learn new skills to make you stronger, faster and befitting to yield that shiny Elven Armour newly crafted with ores you found in a deep mine.  If one is to find an ending to this story, then it will take time as I have realized a few months into this project.  Every inventor ends up making something.  They probably will turn it into a product for most people to use.  But the treasure for the inventor lies in gaining more knowledge and experience.

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New tools

I think I have mentioned before that by education, I am a Mechanical Engineer.  However, this was in the 90’s.  There was huge development in Malaysia to get it gears running.  It was so huge that the country could not get enough talent to fill in the many spaces required.  I had secured a job months before getting mu Diploma. Malaysia’s  Development rapid growth went right up to end of 1997.  In that span of time, one gets to fill up those voids fairly easy once one has accumulated enough experience.  I went into Control Systems, behemoths like Distributed Control System (DCS) and Fire and Gas Detection Systems (GDS).  Right up to the end of my current employment, the process of learning never ends.  Such is the immense volume of knowledge to be mined from this world.

I have now taken up Electronics as a new field of self study.  Prototyping an Arduino micro controller was the door opener.  That is formal engineering.  But learning how to solder is enhancing skill.  I have now acquired basic skills to properly use a soldering iron.  I have now accepted that Tinning the tip of your solder and keeping it clean is very crucial to get the heat on the pad as soon as possible.  The internet helps.  Not just Youtube.com but also forums for hobbyists.  This just made me realized that the older technology is very much relevant in present day.  Data mining is the process.  Before you mine you would still need to do a geological survey of the lands.  That geological equipment is in your brain.  How does it determine?  Some say through experience.  Some would say faith.

Servos

It has been some time before I had any update on this blog.  Much of that time was spent on developing the prototype.  On a daily basis my head is torn between making JUST a prototype where tests can be done on a raw specimen, to actually developing that product into something much closer to production.  I had the original idea to move the spoiler directly from a small RC Servo.  I have grown to appreciate this invention.  It is small yet simple.  It needs just three wires to operate.  In that time to appreciate, I have also come to know of its inadequacies.  Size is important in this project because I need to squeeze it into size predetermined by somebody else who has his or her own design constraints. Size is proportionally related to how big a torque it can generate.  Shall I make it anew or continue on this road to hack an existing spoiler?  Another fork in the middle of the road.

The original idea of directly actuating the spoiler had to be abandoned.  This is due to the design of these servos.  Where the environment this unit has to operate, it would face maximum wind force when the car travels at its maximum speed of 210 km/h.  I have to move the servo away from being the only source of mechanical support to the spoiler.  It is now hinged by aluminium tubes.  Now we look at the force that the servo requires to generate.

The force on a wing is calculated as

F = 1/2 x ρ  × v ² × Cd × A

Where

F = Wind Force in N

ρ   = Density of Air (typically 1.146 kg/m² at 35ºC)

v  = speed in m/s

Cd = Coefficient of drag

A = Surface area in m^2

One thing that we need to understand in this equation is that the Force required to overcome air resistance is heavily influenced by speed.  Now we have to look at the surface area as one that is directly being influenced by the moving mass of air.  Therefore, if the surface is at an angle to the air, one has to calculate this based on the degree.  Based on an freely available educational information, we know that the drag coefficient Cd;

Cd = 1.28 × sin (a)

Where a is the angle of attack or inclination of the surface.  Plus as in trigonometry, we know that the maximum surface area is one where the angle is at 45 degrees.  Any larger, then the Cd would need a different number than 1.28.  We also know that the surface area is a plank with the size of 715mm wide by 90mm long.  Having an area of 0.06435 m²

Now we have the calculated force

F = 1/2 x ρ  × v ² × Cd × A

= 1/2 (1.146) (200 x 10 / 36)² (1.28 sin (a) ) × A

= 2263.7 × sin (45) × A

= 1600.68 × 0.06435

= 103N

Or approximately 10.51kg

This shall be the design constraint for the servo motor.  We need one that can at the very least, generate this much amount of force to be able to move the spoiler.  The HITEC HS425BB has a stall torque of only 4.1kg/cm at the maximum power of 6V.  The servo arm that fits our requirement based on location of the servo and distance to the control arm is 30mm (3cm).  Therefore, the available force from this servo at that distance is 1.36kg or 13N.  If we choose to use the same area of spoiler the capability of the spoiler is limited by

a)  Speed i which it operates and

b) Angle of attack of the spoiler

We would need a servo that generates at least 31kg/cm or 431 oz in or multiple servos just to move against that amount of wind.  Therefore, we have come to another fork in the road.  Single or Multiple?  Looks like this is going to be costly.  This then brings me back to where I wanted to do this project.  A variable angle of attack spoiler meant for reducing operational cost.  It was for the purpose to make life a little bit easier for normal people.  We would not expect them to be running at 200km/h.

Assembly Unit

While we leave the issue of the servo, we look at the other design aspect.  A few days were spent on trying to shoe horn pieces of wood into the current design.  It is difficult but I have found new respect for using wood as building material.  This made me look back at history.  We had woodwork classes back then in the mid 80’s.  We had good teachers.  May they be blessed for passing on the knowledge that I am using now.  Its back to buying wood craft tools such as chisels and planers for me.  A worthwhile investment.  Every stroke of the plane will be followed by gentle fingers flowing down on the grain.  Feeling for inconsistencies.  You cannot escape from it.  Every push of a file, will be followed by a stroking hand.  This is why people were called craftsmen.  It wasn’t for the product they made.  It was for how they made them.

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OLYMPUS DIGITAL CAMERAOne great advantage of using wood as a material is the ability to reduce the weight.  Prior to this, we measured the Fibre Glass material and it weighed in at approximately 1200g.  The wooden assembly itself registered just north of 900g.  It begs to question the need for composite material as a preferred building material.  In Malaysia the Forestry Department makes it a must for loggers to replant the trees.  It is a sustainable building regime only if everybody abides to it.  I would guess that the developed countries find the material takes longer processing time and have that added inconvenience of replanting trees being a requirement.

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Further development goes on as with any challenges in life.