Nifty little data logger

[James Doulton]

I've just had my newest toy delivered. It is a Racelogic Vbox Sport. Let's not mention the price (£249 + VAT). This datalogger measures speed, using GPS, and it takes data samples every 50 milli-seconds. You can connect it up to an ipad or iphone and it will do instant graphs and measurements. It also logs the data to an internal SD card so that you can use it on your computer, either with their software or something else. I imported it into Excel to make my own graphs.

I found a suitable bit of flat road to have a blast in the Legerra and I did two acceleration runs, getting a best 0-60 time of 8.2 seconds. I haven't worked out how to make the best getaway, I just used 2,000 rpm and lots of throttle and got wheel spin for most of first gear. If the gearing was just a little higher then I could get to 60 in second, like the RS2000 did, and that would save about half a second. Because it was at night on an unlit road, I had my distance glasses on so I couldn't really see the poorly lit rev counter so my gear changes were not quite on the 6,000rpm.

The Legerra has a bog standard 2.0 Pinto driving through a 5 speed box to a 4.23 Escort axle. I have 15" wheels with 195/65 tyres giving maximum speeds of 31mph, 58mph, 83mph, 114mph and 137mph in the gears (though I've not gone over 80 for fear of losing my roof).

[Adrian Southgate]

James... My little quip about being a rocket scientist when you joined the club... I think in hindsight I should have just kept my trap shut :-)

After my new engine is run in I'll see what I can get out of mine with a 3.54 english. I don't think my HTC will produce quite that accurate a graph though it does log acceleration using GPS and motion sensors.

[James Doulton]

I had been using a Garmin cycling data logger but that only took samples every second, on the second, with no G sensor. It did have a heart rate monitor though!. This meant that the first job was to try to work out when, in the one second period, I had moved off. Similarly, I'd have to interpolate at the other end to estimate the time when I was doing 60mph. Also, I couldn't tell when I had changed gear or how long the changes took, because there just wasn't enough data.

The Vbox is much better but I still can't see the 2nd/3rd gear change very well and both plots get noisy around the 60mph mark. That may be due to trees or power lines or it could just be a limitation of the device. I shall have to try it again on a different bit of road somewhere.

[Adrian Southgate]

M4 is flat and straight...

[James Doulton]

Looking at my figures again, I realise that I made a mistake on the gearing (because in some calculations I'd used 6,500 rpm instead of 6,000 rpm). So the axle is a 3.89 and the speeds in the gears are for 6,000rpm.

[Paul Sheridan]

I take it that the flat spot on the gragh is 1st to 2nd gear change!  so that looks like 1 second for each 10mph to 32mph, If the wheels were spinning, you are loosing a lot of time there. be interesting to see a couple of runs to that speed with no wheel spin. 

[James Doulton]

2.6 seconds to 30mph. I was expecting more traction than I got. I expected to get 0.6-0.7g but only got 0.5g. If I project that same traction all of the way to 60 then it would be 5.5 seconds. Other rear wheel drive cars get down into the low 4's, so I'm a bit disappointed with the traction.

[Pete Clayton]

Looks a nifty bit of kit. If you"re spinning through first, try doing a run starting off in second

[Adrian Southgate]

Ballast...

Which wheel is spinning, normally its the o/s when going for it in a straight line, the n/s wheel only breaks loose on left handers on mine. I put my battery and tool box over the right side of the boot, the spare rim sits slightly left of centre. A bag of sharp sand (25KG) will add a little more grip to the right rear if you pack it into the rear corner of the boot.

[James Doulton]

To be honest, I don't actually know if it is just one or whether it is both. What I do know is that when I went to do my second run I could see a long streak of rubber on the road on the O/S but I didn't think to look for another one. What a numpty!