3D printed GoPro mount

I've tried various generic GoPro mounts over the years but they all have had problems with vibrations and wind in high speeds, and I've always ended up with securing the camera around the roll bar with insulation tape.

A rough camera mount and a dirty
cage. The cable is to my data logger.

Now I've modelled and 3D-printed my own mount.

I'd love to show a video from when I tested it on track the other day, but unfortunately the memory card was full and nothing was recorded. But I think it will be robust enough.

I'll sand it and put some paint on it some later on.

Bronze bushing

Another try with the front lower rear a-frame bush. Now in oil filled bronze bush, thrust washers and a custom made crush tube. This solution feels rock solid without any play at all! Ahhh inner peace, finally.

So far I've tried standard rubber, Powerflex polyurethane, DIY moulded polyurethane and now bronze.

The upper image is a rendered cad drawing. I'm slowly improving my 3D skills. The image to the right is a photo.

I have an extra set of these parts if somebody would like to buy as a kit. Please contact me.

3D-printed moulds for polyurethane bushes

For a couple of years ago I bought Powerflex polyurethane bushes and replaced the rubber bushes in the front suspension. I was never really satisfied with the small bush in the lower rear a-arm as it felt like they're a tiny bit too small. Also, the design of the bushes does not do a very good job of handling lateral forces. It has always been on my agenda to replace them with something different and now as the play is worse I've decided to take care of it.

There are many ways to make bushes, and I decided to try to mould my own. Partly because I don't have access to a lathe, but mostly because I'd like to see if it would work out.

So I 3D-printed moulds and reused the steel tube from the old rubber bushes. I used some wax as a release agent, and moulded with a 2-compound polyurethane. I let it cure for 24-hours in room temperature, and then 14h in the oven @ 80°C.

The result was surprisingly good and I put it in the car and test drove it. No play and no binding! I don't know how it would hold on track though, but it would probably be fine.

The design of the bush is still not very good because it still doesn't handle lateral forces.

But I have a new plan...

Bad earth troubleshooting

My engine has been a bit "moody" when idling. It can idle smooth, and then suddenly change idling speed. Some of the dash gauges has also been flickering a bit. It haven't bothered me much but today I took my USB oscilloscope and started troubleshooting as I figured it must be electrical. My suspicions were the alternator as it use to haunt me.

But I was wrong. Here is the voltage between the battery negative and the engine loom ground:

I moved the loom's ground connector from a pedal box cover screw, to the engine block. Now it look like this:

The scales are different but you get the point. One could argue that bumps around 50mV won't do much harm but at least now the oil pressure gauge is more stable. It feels like the engine runs smoother too, but that might just be placebo.

Custom moulded ear plugs

I hate ear plugs. The sensation of being inside a bubble playing a video game has got me avoid them except when using power tools in the garage. I ride a motorbike to work everyday, and now when I'm getting older I can feel my ears has been taking a lot of beating over the years.

I've been testing different kind of ear plugs. From simple foam plugs to diy molded plugs. They either leak what can be described as a razor sharp noise, damp too much, or dampen the sound of the engine but not the noise from the wind.

So I decided to get a pair of custom moulded ear plugs and booked an appointment at Hörseltekniska Laboratoriet (Hearing Technology Laboratory) here in Stockholm, who often provide ear plugs for musicians and others with high demands of a good dampening curve. The plugs they recommended are from Bellman & Symfon, which sell a kind of plugs that are suitable for motorsport and that fits inside your helmet.

He filled my ear canal with some kind of foam and waited for it to cure. The silence was almost intimidating, nothing came through. Three weeks later I had the finished plugs in my mailbox.

The plugs are soft like silicone and goes in a long way in your ears. On the motorcycle they're great. I can clearly here the engine, but not the wind noise.

But in the Caterham on the other hand, the engine is just too quiet compared with the wind noise. When I drive with the plugs in at the motorway, I can't tell if the engine is running or not. I have to look at the rev counter to see if it's time to change gear.

As this year is a disaster from track day perspective, I haven't tried them on track, but I can imagine the wind noise is still so much louder than the engine noise, and no ear plug will help me there. I'll probably use them anyway, both for lowering the noise levels and for reducing the sensation of sensor overload.

UPDATE: They work great on track! I feel I even could use a bit more dampening.

3D printed cold air intake

Intake temperature has a direct correlation with engine power. For every 10°C rise in air intake temperature, engine power will be reduced by 2%. Last season I logged intake temperatures over 40°C on a 20°C day, which is really a waste of power.

So I need to duct cool air. I've been googling for different types of air scoopes and naca ducts but prefer not to cut a hole in either bonnet or nose cone. So I decided to try to get some air from in front of the radiator.

As I've written before, my 3D modelling skills suck. But where I work I have access to a 3D printer and wouldn't it be nice with an air duct that goes in the small space between the radiator and nose cone?

I started with a lot of measuring.  I used my kids' clay for the space between the nose cone and radiator, that I cut in pieces and measured. Then I modelled the constraints in the CAD program. I used the loft feature for a nice flow-friendly air duct and started printing.

3D printing is a slow process, and they can only print small objects. I had to split the part in five smaller parts and glue them together with epoxy. Each part took about 8-12 hours to print in medium quality! And it took a few tries before the outcome was good enough.

3D printing, first attempt.
I quickly learned that support stays should be avoided as much as possible.

I also did some CFD analysis to get a design that flowed all right.  I admit it is not perfect, but the first versions was worse...

CFD analysis of an early version

The theory is that the  higher air pressure in front of the radiator will force air into the duct. I've never had problems with high coolant temperatures and I hope it will still will be ok.

The parts glued together with epoxy.

Some filler and black spray can paint. As I didn't want to ruin the existing radiator alu frame I manufactured a duplicate and cut a hole for the duct. When I look at the result I'm amazed that I didn't put just a little more effort to make the end result better looking. But I just wanted to get it finished...

This duct has taken a lot of effort to produce. I've learned the hard way that 3D printing is not a mature technology and have a long way to go. The printer I used was far from a cheap entry level model.

Next step is a better suited air hose and how it will integrate with the filter. I have a temporary solution that works but could be much better. Also some back to back testing and see if there is any improvement.


References:
1. Comparison of Engine Power Correction Factors for Varying Atmospheric Conditions

Rear bump steer

Bump/roll steer check on the rears for the first time, using a laser level on the brake disc and a mirror. I don't know why I haven't done this before. It turned out they (the rears) had quite a lot of toe in bump steer dialled in.

Apparently it is common to set up road cars for understeer and stability by inducing a bit of bump steer - toe in on the rears and toe out on the fronts. On race cars close to zero bump steer is preferred if possible, for maximum absolute grip and less scrub.

I reduced the bump steer by simply switching place of the bump steer spacers and it was significantly reduced. Not quite zero but I leave it there. Now the larger 9mm spacer is up and the smaller 5mm is down - opposite of the top image. (the top image is from the CSR Assembly Guide Supplement document)

I did the fronts for quite some time ago but without the mirror. I must say the mirror method is both simpler and more accurate. The basic idea is to put the laser level on the brake disc and point it forwards or rearwards to a mirror that reflect the beam back to the same point. If the point moves sideways relative to the origin when you raise the wheel - you don't have zero bump steer. Adjust the spacers and repeat.

Airfoil behind roll cage CFD analysis

Does an airfoil generate downforce when placed behind a roll cage? Since I'm starting to get along with the CFD analysis software I did some more simulations.

The airfoil is a NACA 2312 at 160 km/h with 20° angle of attack. Length ~170 cm, width ~20 cm. As I suck on 3d modelling, none of the models correspond much with the real world. Neither the results probably, but can give an hint of what you could expect.

Without roll cage

Scenario 1 - No roll cage, airfoil 40 cm above trunk
Airfoil downforce: 791 N
Airfoil drag: 282 N
Total downforce: 1810 N
Total drag: 1230 N

40 cm

Scenario 2 - Airfoil 40 cm above trunk
Airfoil downforce: 542 N
Airfoil drag: 174 N
Total downforce: 1482 N
Total drag: 1296 N

50 cm

Scenario 3 - Airfoil 50 cm above trunk
Airfoil downforce: 857 N
Airfoil drag: 268 N
Total downforce: 1742 N
Total drag: 1438 N

Scenario 4 - No airfoil
Total downforce: 738 N
Total drag: 1051 N

Conclusion:

A wide airfoil behind the roll cage does generate downforce, but raising it just a bit increase the effect dramatically. To no surprise, the outer parts of the wing are the most effective regions. Real world experiments are necessary to find the optimal location.

Engine bay undertray aerodynamics

Some time ago I started to do some CFD analysis to see if I could do any simple changes that improved the aerodynamic properties of the car, without altering its appearance too much. It turned out that I had too much faith (or more probably - too little knowledge) of what the CFD software could provide me, and after putting in a great deal of work I finally gave up.

It is said that from an aerodynamic point of view, one of the most important features of a car's body design is how it looks underneath, and even if my previous CFD adventures failed it pointed me in the same direction. To fit an engine bay undertray is not very complicated and doesn't affect appearance much, but before I started I wanted to confirm if it would improve things or just be a waste. This time I made a much simpler 3d-model of the car, and had much lower expectations of what the CFD software could help me with.

Standard under body

The results should be taken with lots and lots of salt!

Standard
Drag: 879N
Downforce: 427N

Undertray only
Drag: 793N
Downforce: 455N

Undertray and skirts
Drag: 809N
Downforce: 590N

Undertray, skirt and splitter:
Drag: 858N
Downforce: 604N

All calculations are in an air speed of 160 km/h. The standard design does generate a bit of downforce, because the car body is at a small angle compared to the direction of the air flow. The ground clearance is 15 cm, minus the engine oil sump. The design measurements are just guesses as I didn't take time to go out to the garage and measure. (it does look a bit short). No rounded edges. The body is solid on the upper side.

An underdray reduces drag but doesn't give much improvement in downforce. On the other hand, extending the undertray with a 5cm skirt improves downforce quite a lot. I also tried to add a small splitter in the front and see if that made a difference (see top banner image) but the small gain in downforce is not worth the effort.

One apparent issue with fitting an undertray is of course heat. I have a plan for lowering intake temperatures (more about that later), but if the heat from the exhaust primaries will be just too much and start to melt things I don't know.

Caterham has a ready made undertray on their website, but I've already bought a sheet of 1 mm aluminium and started to cut out the under tray. I'll post more when (and if) I finish it.

MOT, autumn and nothing much

The yearly MOT was a bit different. First attempt they refused to inspect the car as the guy said he'd not manage to get into the car as he was too big. So he sent me home with my money back. I'll never use them again.

When I should do the second attempt I realized the car was just running on three cylinders! With just minutes to spare I found the fault was a loose wire to one of the coils. I managed to fix it temporarily with a piece of wire and insulation tape and got there just when my registration number was showing on the display.

He did the inspection with me waiting in the car, only to get out to pay the bill. No troubles, no complaints.

This year I had the cage still on the car. No-one mentioned it. I won't bother to take it off any more.

I haven't driven the car at all for some time. Today is a cool but dry autumn day so for the first time in a very long time I took a drive out on the country side.

This car is really fantastic to drive!

Just wonderful.

My wheel fell off on a trackday

At 137 km/h coming into a long right turn, my inner rear wheel fell off. A loud clonk and I could see how the inner rear wheel was bypassing me! I slowed down slowly standing on three wheels and could keep the car on track the whole time. A guy ran out on the track to help me, and we could easily push the car out from the track by lifting at one corner while pushing.

The loose wheel had hit the rear wing rivets loose. Other than that, no damages at all! No scrape marks, nothing. I put the other set of wheels on and continued driving the rest of the day as nothing happened.

But how could this happen?

The wheels have been used three seasons. Magnesium centres are known for the need to be inspected every season - but this is aluminium and they're supposed to hold together. Then I noticed that the rear centres had larger bolt holes than the fronts!

I've emailed the manufacturer and got the following replies:

Cracks forming on the other rear

I have spoken to two other owners  with the very same design billets,  I think I only made 5-6 sets like your before changing to the later profile as  the power and weight of customer cars was  going up so I thought to beef them up a little, The two I have spoken to  have no problems and have used them now for three seasons hill climbing here in the uk. I do not have an answer for you why  there has been a failure, but I can Only assume fatigue, The later billets you have are now used on lots of similar cars to your including some saloon circuit  cars around the 850kg mark with no problems reported 
I am of course more than happy to send out replacement centres .

And later:

I see the  old wheel bolt holes are larger, this is because when I originally worked with Meteor  we were going tom use floating taper washer that needed a bigger hole, using these washer didn't work out so I changed the hole to smaller dia, the set you have were simply a set form stock that were used up.

I see the damaged inner rim. No problem for me to send a replacement under the circumstances.

After investigating the new design I'm confident they're much stronger than the one that broke, and I feel assured they'll hold. If you have similar wheels, I suggest you check them and see if you have the larger or smaller holes, and replace them if you do. If you have the new style centres I wouldn't worry.

I must say I got an immediate and professional response from the manufacturer, and they did everything they could have done in this situation. However, I don't think I should have gotten the weaker style centres in the first place.

New style centre from the inside.
 Note that this picture doesn't show that the centres are also thicker than before.

Old centre, with big bolt holes.

New rims with stickers on

New 13" rims from Force Racing, 7" and 9" wide with brand new Dunlop slicks - "stickers".

I bought the rims directly from Force Racing this time and they were very easy to deal with and I can really recommend them.

The rims are very lightweight - only 3792g/3528g according to my kitchen scale* and look stunning.  If you want to order yourself, refer to this post and they know what to do.

Note that you need to modify your rear calipers to fit 13" rims on a CSR!

The slicks are the same dimensions I usually run - used Radical PR6 slicks 230/570/13 and 190/535/13 - but this time in soft compound instead of medium which the Radicals run. We'll see how that goes. I bought them from HP Tyres. The rims are a bit narrow for these tyres, but I think they work ok.

I plan to practice on worn used slicks and put these on when I really want to go for it. I've already started building a simple rack for my trailer.


* - my kitchen scale is known for messing up recipes 

Gearbox disaster

My gearbox failed with a bang on on the King of Mantorp TA-event. Totally unexpected on the day's last cooldown lap. Looking at the log file I didn't even have 50% throttle when it happened.

The good news was it was easy to see where the problem was. The bad news was I it looked rather serious. When opening the top lid everything looked normal which at least gave me some hope.

We don't have a company named Road'n'Race Transmissions here, so it took some effort to find somebody that was even interested to look at the gearbox. As it turned out, the man I eventually found knew a lot about type-9 gearboxes and I must say gave me very good confidence it could be fixed, and with an helpful attitude.

Bertil Carlsson in Vejbystrand, described what have happened as a locking nut had shaken loose, causing the big end nut unscrew itself through the casing. Something that he'd never seen before.

The case was welded, the nut was replaced, and while he was at it he replaced the sync-ring between gear 5 and 6 which was very worn. Everything prompt and for a very reasonable price. (I'm not sure what could have caused the worn sync-ring. The only thing I can think of is that I had a cracked clutch plate a long time ago that made gear changes difficult at high rpm.)

That said - someone (not me and not Bertil) did really mess up the order of the bolt from Caterham, and therefore this little disaster took a big part of the summer. I'm a bit disappointed about this but I guess I should be happy it turned out as good as it did, and that I didn't have to buy a brand new Sadev sequential gearbox with paddles.... ...because I couldn't afford it.

All right - time to put the engine back in and see what's left of the summer!

TimeAttack - "King of Mantorp"

Valtonen Motorsport RX-8

Normally I don't like to compete but somehow I participated a Time Attack competition this weekend. Seven type cars are not allowed in their series, but this time they had a "no limits" class. Some of the competitors car's was completely insane, as the tube frame, all carbon RX8 to the right, accompanied by a complete race team.

Photo: Felix Eriksson

I managed to get the 4:th place. I'm really satisfied with that. Not so much for the final time (1.23,4), but that I kept my head together and managed to get a good run in the super final which was one lap only!

In fact, the qualifying lap and final lap was one second faster than all my practice laps during the whole day!


The official noise check reported 97.5 dbA drive-by which they said they allow today but not tomorrow. I'm getting there...

Everything else worked very good, except....

Gearbox problems!

Just when the day ended something happen with my gearbox on the cool-down lap. I works but makes some chirp noises and the gears are hard to engage. .... .... ghh

Update: I got a couple of seconds of fame in this movie:

Intake cone filter and air pressure

The Pipercross airbox I bough was supplied with a built in air-filter rated up to 200 hp. As don't want to strangle my engine I now have fitted a cone filter with larger filter area.

102mm to 80mm silicone reducing elbow from do88, a plastic tube and three hose clamps from the local hardware store. The filter is left overs from the CSR200 engine.

As I already have a MAP-sensor connected to ECU, I decided to do a road test and see if I could see any pressure drop at the intake. Ideally I would compare the three different filters against each other, both regarding pressure drop and maybe 100-200 km/h acceleration, but I rather not on public roads.

RPM vs air pressure (click to enlarge)

The lowest pressure seen was 0.9918 bar, which equals a drop of 8.2 millibars or 0.82%. In theory that would decrease power with the same amount, or in my case 2.2 hp*. The pressure increase seen on this chart is interesting. I have an hunch of what's happening but I don't have enough knowledge to either explain it or fully understand what the result is. Could it have something to do with air moving but the engine's volumetric efficiency is declining and that causes pressure build up?

I was worried the intake temps would suffer with the filter close to the exhaust manifold, but it appears that they are lower than they used to be with the big sausage type filter and never went above 28°C, with the ambient temperature being around 18°C.

* Source: Four-Stroke Performance Tuning page 26, A. Graham Bell.

Attempt to redirect exhaust noise

As I previously wrote my noise levels are now down to 94-96 dbA on the intake side and 101 dbA on the exhaust side.

In an attempt to reduce the latter I did a quick test to fit a 90° steel tube and point the exhaust towards the ground and see if it made any difference.

The result was a bit unexpected. The exhaust noise went down an half dbA, but the intake noise raised to 98 dbA.

I've been complaining about this before, but noise metering appears to be quite random.

Intake airbox

As I wrote in the previous post the track noise regulations in Sweden has become much harder lately. The current limit is 95 dBA drive-by measured from a 10 m distance.

I've fitted a Raceco silencer and now a Pipercross PX600 airbox. Now the car is much more quiet - huge difference! I can't even hear the revs because of the wind. A quick drive-by test with a cheap china noise meter gave 96-97 dBA but after glueing on some insulation material on the airbox the readings dropped to between 94 and 96 dbA on the most important intake side of the car.

On the exhaust side the noise level is 101 dbA and still too high. I'll try to mount a bend or something to point the exhaust to a different direction and see if that helps.

The airbox have an integrated filter that I suspect rob a bit of power. Next step will be an external filter with larger filtering area, and maybe some cold air ducts on the nose cone side or sides.

The good thing with this airbox is that it can be mounted within minutes if the occasion requires. Direct fit, but I had to remove the steel bonnet/nose cone support tube.

Raceco silencer

The track noise regulations in Sweden has become much harder lately. The current limit is 95 dBA drive by measured from a 10 m distance. This limit is set by the SBF (Swedish motorsport federation) for all swedish circuits.

I know my car sounds a lot more than that, around 105 dBA. So far I've never been blacked flagged but I know it is a question of time. Also I wouldn't mind if the car was quieter as I'm not a big fan of loud noises.

The first step is to quieten the exhaust and that is now done with a Raceco 2.5" titan silencer built by Mike Riley. The high price made it a painful decision but it is very nice built and also a lot more quiet than the previous silencer. It take the edge of the bad part of the noise and what is left is a nice round sound. In fact the exhaust noise is now masked entirely by the (very nice!) induction noise.

It was a straight fit and no brackets needed to be fabricated.

It is also a bit lighter than my previous silencer - about 1.5 kg.

The car is much more quiet now but I think it still have a bit to go before I reach 95 dBA. So trying to reduce induction noise is next step.

Rear diffusor and front splitter inspiration

I more or less gave up on my CFD simulations. At least for a while. I could not get consistent results and the obstacles were just too many to keep me carry on. But before I gave up I did some simulations with an engine bay under tray and a rear diffusor, and according to the simulations it did quite a big difference on both drag and downforce.

Today I received some inspirational pictures from Paul Cardy on his previous CSR. I think I'll try to do something in the same lines.

Paul writes:

"The diffuser was attached to the chassis using these brackets with threaded inserts as per picture 1, the rear end of the diffuser was held using these hanger brackets in picture 2, and the main body was held in position using P type clips with steel surrounded by a rubber sleeve and clamped round the chassis tubes. 

The diffuser was made by Freestyle in fiberglass and I had him glass in some carbon on the last section for the look. I made up the front mounts and cut up the diffusers to fit as this was the first ever to be fitted to a CSR so its was a make it up as you went along. 

The front splitter is a sheet of carbon cut to shape its fixed to the chassis with the P clips again. The front upright section is aluminium folded and cut to follow the underside of the nose cone and fixed to the splitter its wrapped in black vinyl."

I also would like to cover the engine bay. But before I do that I must take care of the already high intake air temperatures. But that is a different subject.

Aerodynamics - CFD simulations

After some vacation reading of the book "Race car aerodynamics" I have had lots of thoughts of how to improve the car's aerodynamics, especially the lack of down force.

The common approach on this subject is that the seven is a hopeless case and don't even bother. That might be true, or could it be the other way around? Since it does have the aerodynamic properties of a brick (or worse) - even small mods can make a great difference?

One problem is that you don't want to change the classic look of the seven. That is also true for a majority of seven owners. But I believed something like a flat underside could make a big difference. You can also add removable elements that you only have on the car when you're really going for it.

The question was, how much can be gained, and is it worth the effort?

Autocar did an article a long time ago (?) about wind tunnel testing of a Caterham. You can find it here:
#1 #2 #3

Some time ago I did some simple simulations of how much some downforce would affect lap time. The result was that 160N more downforce @100km/h would shorten the lap time with over a second! As a reference, F1 cars generate more than ten times of that, at the same speed. (source: the book mentioned.)

Wind tunnels are not accessible for most of us. At first I thought I would do road testing with string potentiometers measuring the suspension compression and connect it to the data logger. Straight roads are not that easy to find where I live, and going 200+ km/h on public roads are not that great either. The number of variables are endless and if something works or don't work I probably won't know why.

The book mentioned above briefly talks a bit about CFD - Computational fluid dynamics - and concludes that it is very expensive, complicated and not something for others than high end race teams. Well, time has passed since the writing of that book, and now the CFD software is not that hard to use and 30-days trials can be downloaded over the internet from many different software companies.

It turned out that the book was quite right. After experiments I now understand why top race teams still use wind tunnels. CFD simulation is very complicated, and it takes lots of effort to get accurate results. But for rough estimates it could still be very useful!

Baseline

So I made a rough simplified CAD model of my car. It may sound easy, but for a complete 3D modelling newbie it took quite a lot of time learning.

I started with high ambitions, but after a while I lowered them just to get some results at all. In these simulations the wheels are not rotating and the ground is not moving.

@160 km/h
257N front downforce

1935N drag

Note, these are rough numbers. 

I use to complain about front end lift when I drive, but this is pretty much the opposite. 

Anyway I plan to do some changes to the model and see how it affects the output. I also plan to investigate some individual parts in detail with finer meshes and higher accuracy.