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.

 

Adjustable Spoilers Part 3

I have purchased an Original Copy of an R3 rear spoiler for the Satria Neo to work on as a working development platform.  It is made out of Glass Fibre.  I normally would not do this if not for the fact that I was the told that the real deal would take some time to be ready.  I had gone to the Proton Parts Centre in Glenmarie, Shah Alam, Selangor to buy some parts for my other car.  I had asked for two sets but was told that it is not normally held in stock.  I was told that these parts do need to be back ordered.

Since what I am trying to do is make a full scale mock up and as a real working unit for further tests and development, I guess it would be ok.  It costs RM 140.00 which I purchased from an accessory shop called Brother’s from their main office in Kelana Jaya, Selangor.  There are actually two models of similar looking spoilers.  The difference is on the mounting holes.  I bought the proper one and took two more days before doing something about it.

I transferred dimensions from the spoiler to the wooden prototype wing and vice versa.  The wooden wing was wider than the spoiler’s trailing edge.  I chose to cut by 40mm offset from the shoulder of the trailing edge.  The hardest part was trying to cut it exactly straight as the spoiler is curved on all axises.  I used another straight wooden piece to make it straight.  I used a wooden saw, a dremel and a powered jigsaw.  And it came out shitty.  In retrospect, I should have just used the jigsaw.  I just had to be steady with it as an oscillating power tool is difficult to hold steady.

Severed Wing

Severed Wing

 

Once the trailing edge was cut, I tried placing the Standard Hitec Servo Motor around the cavity to see if there was room.  This has been the main question in my mind for weeks.  If the servo was too big, additional modifications are needed which would drag my schedule longer.

Servo Fits!

Placing the servo for fit testing

You can see from that picture that the Glass Fibre wing was made in several separate pieces.  Where they mate and glued to each other, there is some internal projections that hampered the fitment.

While finding placement for the servo it dawned on me that it would be easier to use the glass fibre cutoff as the moveable wing.  All it need would be to fit wooden pieces at either end.  These wooden pieces would then act as a swivel point on one end and a driven end at the other.  The driven end would only be a place for me to install a Servo Arm.  Then it occurred to me to measure the weights of the wooden wing and cutoff to compare.

Weight of Fibre Wing stands at 650g

Weight of Fibre Wing stands at 650g

Wooden Wing

Wooden Wing weight is at 442g

This appeared to me as simply amazing find.  While it is well understood that Glass Fibre is light and commonly used as lightening body shells, in this case; wood would be the ideal material.  Wood has very good compression properties.  In a spoiler, there would be some downforce on the top surface and wood would be excellent in this aspect of design.  It is strong while remaining light.  The negative side of it is its long term condition when exposed to wet, hot and humid weather of the tropics.  A nice light coat of shellac or even Plastidip could help reduce that.

While I had the wife’s baking scale out, I weighed the remaining part of the glass fibre wing. It weighed in 1073g.  In total the whole glass fibre wing would then be in excess of 1.7kg.  If we replaced that with wood, we could see a weight savings of more than 20%.

1073g

1073g

This could lead to replacing most of the structure into wood.  Saves fuel consumption by making a cleaner aerodynamic profile while saving weight!  Looks like I am onto something good here.

Adjustable Spoilers Part 2

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.

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Finished Test Rig

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

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Close up of Hitec HS-425BB RC Servo

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.

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Adjustable Spoilers Part 1

I have mentioned in some random postings on the internet of the need to have malleable aerodynamic surfaces to reduce drag in different driving conditions.  In fact Autospeed.com has mentioned this as a stumbling block in automotive design advances.  Articles such as this one has given me ideas about changing the effect of rear roof spoilers from just providing small down-force and drag to actually help reducing wakes.

Good spoilers

Spoilers to reduce wake meant for big profile vehicles such as MPVs and SUVs

 

Since I mentioned about Arduino in my last post, I have actually bought one from RS Online Catalog.  I have the Starter Kit for Arduino Uno which comes with lots of bits and pieces.  I have mentioned that I had never dealt with electronics before.  The most I have done is fondled with DC circuitry.  Hence an order was given and the money was pumped into the Open Source community. I hope they use it well.  I received the box and was amazed at the amount of things Malaysian Ringgit could buy.  When I say ‘the amount of things’ it is not about the quantity of odds and ends.  Its about reusable components.  This Starter Kit is amazing in terms of what things you can make with it.

It took me yet a few more days before I started fiddling with it.  I blame it on my age.  A child would rummage through it without a second thought.  A teenager would plug it in first and jump for joy to see the yellow LED lit up.  A twenty year old would skip all the pages and build it up with the first drawing.  I am 45 years of age.  I read every single page of the manual and tutorial first.   Even then, I went to the website Arduino.cc to have a look at the specifications of the blue thingy that i a permanent resident at the side of my bed.  Its entirely ok.  My wife has her TV/Android phone/ Android Tablet as companion.
I have this.

1798771_10151988477308107_89366630_n

It started with this

What that thing does is move the servo using a potentiometer.  The LCD shows the angle in degrees from the readout of the servo.  The LCD is meant as part of the development of what I intend to build.  I would use it to adjust the angle while doing testing.  I will adjust the angle of deflection and see the effect on the fuel consumption via the on board FC computer.

Yes that servo is tiny and has a stall torque in oz-in.  It came with the starter kit.  About mid of March I bought a bigger servo from MyDuino.com  and its a markedly bigger in size and now I have something that pulls in kg-cm.  The intention is to move a piece of aerodynamic surface as part of my car’s rear spoiler.  I have calculated that for a 1m span, the wind force acting on it at 200km/h would total 1.4Nm2.

A discussion on these sort of spoiler is well documented.  I have to admit that it does not contribute much on the actual down-force required for a front engined front drive car.  In fact, when looking at the profile, it would also provide less drag.  Quite simply when the designers made this, it was never meant to provide much effect other than cosmetics and form rather than function.  Proton now understands to sell it, it need to look nice.  Unfortunately.  In essence, the design and flow of the spoiler is very fluid.  This suggest a high amount of design work was invested in this one piece of fiber.  There is no argument that this part actually sells more of the car than any other body kit.  It is therefore wise to preserve the design as much as I possibly can.