Xoomcentre First Look

I've been playing with Xoomspeed's Xoomcentre, which has been recently modified to import CSV files.  Download it here.  It's extensible with plug-ins that you can write yourself and it's really quite easy to use.  The CSV importing is brand new, so it needs massaging of the CSV files to import correctly.  It's also reliant upon GPS longitude/latitude data to accurately report the run times, so as my RacePak logger doesn't output that information, I don't get the run times and I have to manually set a few things like graph ranges as the time slip shows massive variations after the finish line!

Despite these shortcomings, I've been able to make good use of the software to show me things that I've never been able to see with the RacePak software.  I've written a plug-in to handle the RacePak CSV format and it's now a breeze to import any of my logs.  As a test, I decided to compare my final run at the Dick Mayo Sprint at Castle Combe in 2011 and 2012.  I imported my 2012 data, set it as the reference run and then imported the 2011 data.  After removing the friction circle graph and gear data, I added speed from the reference run to the 2011 graph.  It took 90 seconds from start to finish and this is what I was left with.

2011-2012 Dick Mayo Sprint Data

In 2011, I managed a 68.29, whilst the 2012 run was a 66.57.  The graph hasn't lined up perfectly and there's an error of almost 0.5 seconds in favour of the 2012 run, yet the official results show the 2011 run was faster in the first 64 feet.  From then on, the accuracy is much better, so I'd put this inaccuracy down to the inaccuracy of GPS at low speeds.  Immediately, it's obvious that in 2012 the car was a little faster from 40-90mph.  This will be down to the gearing, which was shorter in 2012 thanks to the 14 tooth front sprocket replacing the 15 tooth of 2011.

Moving on to Quarry, I was tentative over Avon Rise in 2011, some 8mph slower in places, having lifted off over the crest and this cost a tenth.  The downshifts happened in a similar manner in both years, whilst in 2012, I carried 6mph extra apex speed gaining another 0.16 through the middle part of the corner.  The lighter weight and bigger rear wing were likely to be good reasons why I was faster, allied to greater familarity to what is a surprisingly tricky corner.  The higher apex speed resulted in a faster exit, which led to a 2mph run down the first half of the Farm Straight, netting a further tenth until the longer gearing of 2011 caught up thanks to one less upchange.

At the end of the straight, I was much more agressive in 2012, braking 35 metres later and gaining 3 tenths.  I lost two tenths of that with a lower speed through the first half of The Esses.  From memory, I'd braked too late and missed the apex.  It was even by the exit though and pulling more revs through Old Paddock from the different gearing meant another half a tenth.  At the end of Hammerdown, the ratios pulled another half a tenth and I again braked 30 metres later, being some 15mph quicker on the way into Tower and making up a whole six tenths from the braking point to the apex.  Despite the massive gains, I'm sure there's more to come here too.

A higher apex speed and better gearing going down to Bobbies netted another half a tenth, followed by a further half a tenth on the brakes into Bobbies.  The final time came from getting on the power earlier out of Bobbies and I gained another half a second in the process.  In summary, I can see that there was a marginal benefit in the shorter gearing, but that most of the improvement in lap time came from behind the wheel with increased knowledge of the track and a bit more bravery.

Most importantly, this shows how quickly and easily I was able to review the data with Xoomcentre and whilst the export of the graph could have been quicker, it still took less than a minute to do.  I shall be reviewing all my data with Xoomcentre from now on - my laptop might even make it to the paddock for lunchtime reviews!

2013 Season Approaching Fast

It's been four months since my last post.  I had a winter project, but with a lack of time to work on it in November and December, I'm out of time, so that's shelved for the future and my attention has turned to getting the car ready for the new season.  The focus is on fixing broken parts, reducing weight and reducing drag.  It's clear from last year's data that there's too much drag on the car as it runs out of puff down the straights at Combe.

The rear wing is a big dual plane device after last year's upgrade and hanging it high up in the airflow means it not only gets nice clean air for best downforce, but it also adds to frontal area, increasing drag dramatically.  The simple fix is to move it downwards and rearwards to fit behind the rear wheels, slightly above the exhaust.  There's two main benefits to this; a reduction in frontal area and corresponding drag and better interaction with the underfloor thanks to the proximity to the diffuser exit.  A tertiary benefit is that the proximity to the ground allied to the large end plates means it will benefit from some ground effect.

Rear wing goes rearwards

The sidepods are effectively working as big parachutes.  Whilst I cut the front open last season, I found no way to exhaust air from the rear, so the high pressure air from the wheel arches is collecting in the sidepods causing drag and lift.  I've worked out that a single aluminium panel can be cut simply with two folds to replace the existing sidepods.  The sidepods will provide a good exit for air from the wheel arches, exhausting it to the side, with the whole sidepod weighing around 7kg.  This should give a weight saving, reduce drag and reduce lift.

The new sidepods also provide an opportunity to add a small front diffuser to the trailing edge of the front splitter, which will again be cut from a sheet of aluminium with 6 simple folds.  The final piece of aero work is to block up the air intakes on the front clamshell as they are causing a buildup of high pressure air under the clam-shell.

Most importly, the broken things need fixing.  Fresh oil and new rod-ends to replace the broken ones on the front uprights are the key things to fix.  The rear wing endplates also need re-attaching as the existing mounting isn't up-to-scratch as well as a replacement spacer between the main plane and flap.

Sidepod Ponderings

I've been wondering whether the previous diffuser design knocked up last winter was too conservative.  Given that there's no regulations over the shape of the underfloor, why should I start the diffuser at the rear of the chassis?  Why not start it behind the front wheels?  The sidepods are not structural and there's space either side of the chassis.  This brings the centre of pressure forwards and provides a much larger plan area for the tunnels, thus a little more downforce, I hope.  This theory would allow a tunnel each side of 3.1m, which means that even an 8 degree angle would result in a tunnel exit of around 43cm.  That's high enough to mean that the driveshafts and wishbones will have to penetrate the tunnels and also high enough that the rear bodywork (~45cm) will practically meet the trailing edge.  In fact, here's a quick graphic to show just how large the tunnels would be.

Sidepod Tunnels

The tunnels can simply replace the existing sidepods.  Two pieces of flat material are all that are needed to fabricate the replacement sidepods, so it's easy to build and, if I pick the right materials, I could save a good amount of weight as the sidepods are made of beefy fibreglass and clearly overweight.  In order to fit the new sidepods, I'll need to relocate the radiator, oil cooler and the exhaust.  The radiator can be canted over and placed over the tunnel.  This raises the centre of gravity, but hopefully not too much.  The same can be done for the oil cooler on the other side of the engine bay.  The exhaust is not so easy and I'll have to come up with a solution to that.  The final thing to think about is that in order to get it on the trailer, I'll need to pad out the bed so the car sits a couple of inches higher and clears the front crossmember of the trailer.

So there's a weight benefit, but can I quantify the aero benefit without trying it out?  I don't think I can without decent CFD and that's beyond my means.  So the question is whether I fancy spending the time and effort on something that looks like it should prove beneficial.  Comments appreciated!

IOIO Schematic

I've knocked up a quick schematic of how I'll be hooking up the sensors to the IOIO.  The brake pedal switch is too noisy, so I'll tie it to ground normally, with the switch pulsing high.  Wheel speed currently grounds the pin, so I've done the same and tied it to ground with the sensor pulsing high each revolution.  I suspect WifiLapper will pick that up rather than the grounding of the pin I'm doing at the moment.  I'll also hook up the fuel sender, oil pressure switch and oil temperature senders that are currently unused.  After that, I'll work out a strategy for the sensors currently plugged into the ECU.  I need to be sure that tapping the sensors does not affect the ECU and that I can get a 0-3.3v signal.

IOIO Schematic

Broken Rod Ends and IOIO Updates

I nipped out to the garage last night to investigate the cause of the dodgy steering at Llandow.  We'd ascertained that the top rod end holding the upright to the wishbone wasn't firmly attached to the upright, but was it play in the rod end, the interface with the upright or the bolt?  It turns out there's the best part of 1mm play in the rod end.  By the time it's multiplied out to the edge of the tyre, it's a lot of free play in the steering and a little camber too.  It must be a faulty batch as both sides have failed and they were brand new before the Dick Mayo Sprint, so they've done 4 laps of Castle Combe, 10 laps of Curborough and a few dozen laps of Llandow before failing.  I have spares as they were only replaced due to unknown age, rather than wear.  I'll order up some new ones too.

I also had a look at the data from the IOIO.  There's no wheel speed data coming in.  I'm not sure whether it's looking for a high or low signal.  Also, as I'm just grounding the pin, it's very noisy when not grounded.  I'll connect it via a resistor to ground and another to +3.3v and use the switch to either ground it or tie it to +3.3v and see which works.  The brake pedal sensor was successful and you can easily see when the brake's applied.  I'll do the same wiring as the wheel speed sensor to remove the noise though.

Also broken on the day was the gear shift.  I've replaced the 6mm bolt and nut and lubricated all the joints, which seems to have freed it all up.  The spring has definitely not broken as you can feel it by hand once the linkage is removed.  That's good news as it's probably an engine out job to get to it.  There's still some play in the linkage, but it's minimal and I think that's all in the rod ends.  At some point, I'll weigh the linkage as it's quite substantial and that might offset the weight of the paddleshift kit, making it a more attractive option.

The final piece of work is to fix the second plane of the rear wing by attaching a slot gap separator again after the last one fell off at Llandow.  I didn't prep the surface for the epoxy, so it came off with all the vibration.  I also need to sort out something neater and tidier than the bits of skirting board I knocked up to get it in place quickly over the Summer!

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