Con rod machining

The con rod has been machined!! it looks quite good, prior polishing and final work on the bearings. On the sequence below you can see the different machining stages.

The material used on the con rod is 7075 T-6. The bearings are LM-7 Zn bronze, with the top one pressed in and the main one being split. Bolts are M2.

At 14000 RPM the con rod sees a maximum compression load of 820 N and a maximum tension load of 391N. Coefficient of safety is n = 4,4 static and n = 1,1 fatigue (infinite life). I expect fatigue wise it will be safe as 14000 RPM seems quite optimistic for the first test engine for both speed and life time.

After polishing the part will look even better. I will polish it to remove all the tiny notches and sharp edges which will make it look better and improve fatigue resistance.

I will make the split bearings with a tang on each one, and a dowel pin for the real engine. This will improve fitting quality and repeatability of the tolerances.

Next part is the piston, which is one of the most exciting parts of the project.

Renault F1 monocoque manufacturing

Just a little insight on how to make composites. This post is related to the Renault R26, already finished some years ago, to show what can be done in composited by the model engineer.

I have to say, this process is very similar to the real thing, and I can assure you I know what I am talking about.

The process is usually the same for every part: design component - design tooling - patterns - moulds - laminating - trimming/assy. The first two are down to you, so we will focus on the actual making-bit. Just a brief note on design. CAD is very powerful to assist production engineering with templates, 1:1 plots, etc. it is not just the 2D drawings, not to mention CAM, so worth considering for any project.


As an example, see below the engine cover and monocoque. Both made in a similar way: basically, the pattern is the actual shape of the part, but made form a solid block of material that we can shape easily, in this case MDF (wood). The better the pattern quality, the better the mould quality and therefore the part. Patterns usually last only one pull, but enough to get a mould, from which several parts can be made. The mould is the negative shape of the part, if you see what I mean.

Paper templates (1:1 plots) are made which are the cross sections of the part to make at certain heights. Each section correspond to a MDF board level that will be stacked to create the rough volume.
After cutting the boards, they are bonded using glue. You might want to pin them to guarantee alignment.

Rough cuts are made using chisels, files, saws, etc. This is quite an elaborate process. Use templates in all the directions required to ensure the shape is within tolerance. Make as many templates as you need, e.g. cross sections every 20 mm. 

Finishing touches using a Dremel. Use also sanding paper to shape by hand the form. Remember that after this all the little holes and gaps will be filled with body filler, which makes things easier at this stage.

Body filler and paint are applied after the finishing touches. At this stage, the surface has to be spotless as this is exactly how the part will look like.  Use good quality paints to prevent reaction with the epoxy resin and release agent. I recommend car body panel paint.

 Apply the release agent and start laminating. In order to draft the part, a several mould pieces mould might be required. See below how to make the splits using panel board to create the bolting flanges. Use plasticine or other paste on the corners to seal the edge of the board to the part. As cure occurs at room temperature, you can use almost anything. Do one mould piece, cure it, and remove the board from the next section to make another mould piece. This has to be repeated as many times as required until all the mould pieces are completed. Do not remove mould pieces during the sequences so the flanges match perfectly from one mould piece to the other. Drill the mould flanges for bolting the mould pieces together during laminating.

When the mould is ready, make the part with the required material and layup thickness. For most of body work, only 2-6 layers are required. Use more material on corners and bolting sections to reinforce high stress areas. The winglets and other elements of the engine cover where manufactured separately, even with different materials/processes, and bonded afterwards. This applies to chassis, floor, gearbox, etc. where many elements of the car are mounted too. Fit inserts and other bits inside during layup to create hard pads for tapping or bolting later on.

Use again body filler for finishing the part and achieving a nice surface. Prep the surface for paint and go for it!

Based on this process, all the other parts of the body work can be made. However, other processes like thermoforming, 3D printing, sheet metal fabricating are also required for particular parts, like end plates, brake ducts, etc. In real F1 world, the process is based on the same steps, but enhanced with the use of better equipment and materials. You might want to take a look at the pattern post  for a more advanced way to make components (http://bernimodels.blogspot.co.uk/2012/11/tooling-wing-test.html). For the Red Bull 1/3 I am planning to use CNCed patterns, although for big body work pieces, I might stick to the process on this post due to size/cost restrictions of my equipment.

Con Rod manufacturing IT3

Work has begun on the con rod. I will be extending the post as I work along this part and the next parts untill the engine is finished.

I have started with the blank and the machining fixture. All this will come together as what you see below.
More to come :)

The bearings are already finished for it, but will not be mounted until the body and head are machined. After that, the bearings will be reamed to achieve the final bore tolerance for the crankshaft journal and piston pin.

General view IT3 engine

Due to recent job change and house moving, I have not been able to put as many hours in the workshop as I would have liked. This will stay the same for a few months so I will concentrate on getting the main scheme of the car under way and start with the actual car design. This means the IT3 engine will be finished later but still on time to gather relevant info before the important design decisions on the V8 engine are made.

Some screenshots on the engine design almost finished. At this point it is missing spark plug and ignition hall effect sensor, and other sensors (Temp, Engine speed, Inlet pressure, EGT), carburettor, exhaust and engine stand.

The image below shows a cross section of the engine assembly. It clearly shows the main section of con rod, crank shaft and piston, on the lower part; and the exhaust valves and cam shaft on the upper part, behind the rocker carries section. Note the minimal cross section of the piston, quite innovative on an model engine of this size. The bore is Ø35 mm and stroke is 20 mm. Not quite to scale, but this allows for bigger engine capacity and thus more power, without significantly affecting overall engine envelope. Obviously the big flywheel will not be used on the V8 engine. On this test engine it will be used to, first provide enough inertia for the engine to not stall at low revs, and secondly to allow measuring the rough power of the engine.

Below is the entire engine, showing mainly the distribution system. On the V8, this will be different as only gears will be used. The depicted arrangement was chosen to test the gear system, but a chain is used to keep cost and complexity down.

I do not intend to bring into the CAD assembly all the fixings and other mechanical elements to reduce amount of time on design. Since this engine assembly is not too complex, it is worth taking the risk of not playing around with hundreds of fixings in CAD.

Overall very excited to start with the scheming of the car. I might start doing some 1:1 plots to start sketching by hand on it. Even perhaps a cardboard mock-up. This is always a good practice as it is the only way of getting a feeling on the size and helps a lot with packaging (engine, cooling system, control systems, batteries, etc).

More progress with IT3 engine

After a few months without doing much work, I have been putting in some hours in the last weeks at the workshop. It is nice to start seeing the parts in real live that I have been designing for some time, although it has been quite painfull in some instances. Camshafts, cranshaft and valves are all quite triky to machine for its geometry, tolerances and material of choice.

I have been doing external parts of the engine first, then internals that require turning and will finish with internals that are mainly milled. It is intersting to see the nice learinign curve from the IT1 to the IT3 at all levels: resources, cost, materials, design techniques.

Every component requires a lot more time to manufacture, and uses the equipment´s capabilities more extensibely. One noticeable example is the engine head. On IT1 it was made with 3 axis machining, with two main ops. On IT3 it has to be done with 4 axis machining, and it takes 13 ops, aproximatelly 10 times as much machining time, and 6 times as much cost in cutting tools. This is true for most of the parts and will have a big impact on final cost of the V8 engine and time required to manufacture.

On the design side of things, although it is more complex, it is more enjoyable. The better I learn how to use my equipment, the freer design becomes. On the other side, there is still a limit of resource and times available, although this will be enhanced with the use of DMLS and rapid casting techniques I am planning to use for most of the engine external and structural parts. I am considering outsourcing some components of the internals as cost would not be that high compared with the amount of time and tooling costs it would take me.

See some components that I have made so far, although not fully finished:

I have made now the 4 valves that will be used on the IT3 (2 exhaust valves and 2 inlet valves). The one on the picture below is a inlet valve. The stem has Ø3mm on its sliding surface, and Ø2 mm on the wet section. The valve head is Ø14 mm. On the image, the valve still has some material to be removed at the top. I will do that on a secondary op, as the top needs to be grinded to achive a high level of flatness and height tolerance. Material is stainless steel AISI316L for both types, and was not too hard to machine.

 Cam shafts. there are two camshafts, that operate the inlet and outlet valves separatelly. They are slighly different, as the pitch between the IN valves is different to the pitch ont he EX valves. This arrangement allows the maximum valve surface with a given cylinder diameter. The material for the cam shafts is EN24T and is quite hard to machine. At the stage shown, the cams have not been milled yet. For the IT3 engine I will mill the valves, with interpolation as the tests I have made are quite good. See the next picture below. The cam profile was calculated in Excel, then transferred in Catia using a macro, and then into Visual mill. The profile is different from EX valves to IN valves. I will post more pictures after the cams have been milled. The millign of the front flange is also missing, and it will accomodate the features to connect the timming gears. Both cam shafts, have a Ø8 mm diameter on the main shaft, and are bored to Ø6 mm, making it quite light. I will try to keep this arrangement on the V8 engine, although it will be a challenge to drill such a lenght in this steel.

Below is the sequence of pictures of the crankshaft machining. It is also made in EN24T, and is quite hard to machine. The nice thing is that it is turned using this arrangement, rather than with the chuck. This is to allow the turning of two differnet axis of the main and rod journal. I started with a billed of Ø30 mm in diameter. See the bracket on the left to spin the part that I made. 

Below is the first op finished. This is basically the turning of the main journal, which consists of different diameters, that will be used to fit the timing sproket and the fly wheel. On this engine I have not added any feature to spin the engine. I will rather use a friction wheel on against the fly wheel as it is quite a big one (for what I am used to). The main journal is Ø10mm and the rod journal is Ø12 mm.

 The next op consists of milling the material around the rod journal, rather than turning it. I just did it like that because it is much safer. See as well, that the cranshaft now is fixed on the secondary axis, ready to turn the rod journal. The next picture shows the rod journal being finished.

The next steps are to mill the camshaft to form the counterweight area, and key groves for the timming sproket and flywheel. There will not be any oil passages on this one, to simplify the component, it will use a splash type of crank case. 

Below is a picture of my workshop being busy on a late dinner time. Many more to come.

Test engine IT3

After a while of not wrinting any post I finally found a minute to show some pictures of the engine I am working on. This is a single cylinder test engine, which will be used to test the design of the V8 cylinders. The design is almost 100% complete but I have already made some of the main parts.

I will be posting more often from now on. The next two pictures are from the engine head - quite a lot of machining!

These is the engine head rockers bracket. There are two per cylinder. It is quite an original design but I do not think they will make it to the final V8 engine design.

This is the main engine parts put together. The cam cover is missing.

 This is one of the split bearings. It is quite hard to machine due to the tang for locking the position in rotation. It is all made on the milling machine, using a rotary table.It is accurate to 0.01 mm in all dimensions, which is quite an achievement bearing in mind my equipment.
You can see I also do drawings for every single part to keep all the details for when I start designing the V8 engine in a few months.

Dynamic Vehicle Simulation

The last step of the preliminary design is to find out the actual overall performance of the vehicle. For this purpose, I use a MatLab coded 4 corner vehicle simulation, which I developed as my dissertation.

I will not get into much details about the model. In short, it can simulate the forces, accelerations, speeds and travels of each corner of the car, including sprung and unsprung masses. Additionally, it simulates engine and gearbox functions, as well as aerodynamic effects.

After completing the weight estimation and aerodynamic study, the data was input to the MatLab code to simulate a series of maneuvers: pure acceleration, 180º corner and chicane.

Basically, I wanted to find out how the car would perform and if this would be equivalent to the real F1 car.  Let´s take 5g as maximum lateral acceleration of the 1:1 car. At 1:3 scale, this acceleration would be 3 times smaller. Not the force, since there is mass involved, but it would be the acceleration. This is considering, the car has a turn radius of also 3 times less, and speed 3 times less as well. Therfore, the Lat Acc we are looking at is 1,67 g.

In order to run the model, many parameters have to be introduced: polar moment of inertia, masses, inertia of the wheels, engine torque curves, aero parameters, suspension stiffness, and a few more. The CoG is calculated on a quick estimation from the DMU, assuming some masses. The mass is estimated at 12,5 kg, which would be excellent to achieve.

The Tyre model used is a simplified version of Pacejka. The maximum mu coefficient is 2,2, similar to a good racing tyre. I might have gone a bit optimistic here, but the actual values should not be too far. In order to properly find out, I will perform testing on the R26 tyres at 1/5 scale. The tyre construction for this car will be similar.

The simulation is run by a series of driving inputs, that control steering and throttle/brake inputs, as a function of time. After the simulation is run, the results pop up like this:

Therefore, the important results are:
Max Lat Acc: 2,6 g at 120km/h.
Max Long Acc (from a simulation not shown):1,2 g, but average from 15 to 100km/h is 0.56.
Max Speed: 130 ish km/h.

Considering that some of the assumptions might be a bit optimistic, but that there is also room for improvement on the aero side, this results are quite satisfactory. The car will perform slightly better than a scale 1/3 F1 car and will look fast.

Interesting to see from the tyre slip values, is that the handling is very understeering. This is due to the CoP position, which is way too far on the back. I expect to be able to correct this by improving the front wing performance. Testing the simulation with a CoP just 50 mm behind the CoG, an increase of 15% in Lat Acc is obtained.

Next steps is to complete the DMU more components, and perform composite test coupons to gather material data for FEA.