Speedo Cluster Software Updated

Last night, I did my first software update of the Speedo cluster since it has been in the car.
It was a tiny bit stressful as the programmer I use also erases the boot code in the PIC (uProcessor) so there is a window of time where if something goes wrong, or if I make a mistake, the speedo is "bricked". That would require having to pull the whole lot out to be able to get at the emulator connector on the circuit board inside the speedo housing - lots of work. (I bricked the speedo a number of times during it's software development so it's not beyond me to "get it wrong".) It all went well.
 
The update came about following the speedometer inaccuracy mentioned a couple of posts ago. Woody from the AEVA forums sent me this extra gem of information about tyres.
http://www.carbibles.com/tyre_bible_pg4.html#slr

Another website I found also supported this although it results in slightly different figures.

TRC Calculator
(Link fixed)


The combination of different differential ratio and the 0.96 rolling curcumference correction (from the above articles) completely explains the 67km/h vs 60km/h error - although I'm still perplexed at why anyone would have changed the diff in the first place.

So I have altered the ODO and Trip meter calculations to use the 0.96 compensation but left the speed calculation about 3% high - just by not applying this compensation. It also appears (from the second web link) that the static and dynamic rolling curcumference can change. It moves back to about 0.97 at 60km/h and probably changes more at higher speed - getting closer to calculated value. This of course depends on initial tyre inflation. I don't think I'll go that far but I will measure the static circumference of the Hancook Enfren LRR tyres when I get them using a driveway/chalk rolling test.

Speedo Inaccuracy Explained (mostly)

The tyres I plan on using are 185/65R13. With the Vogue's 3.89:1 differential ratio, that works out to be 41.48km/h at 1500 RPM. In the speedo software I divide motor RPM by 36 (41.67 from 1500 RPM) and round up to the nearest integer so it should show 42km/h.
I placed the Vogue on axle stands last light and locked the controller's maximum motor speed to 1500 RPM.

I set the PC to monitor various controller variables including actual motor RPM.
Flooring the accelerator gave me 1499.9 RPM on the PC monitor and 42km/h on the speedo in the car.

So all the calibration and calculations are actually correct - so why does it show 67km/h when we are doing 60km/h?

About the only thing left is the diff ratio - but that can't be wrong - can it?
Historically, the Mk3 Vogue sedan was shipped with a 3.89:1 diff. The earlier Mk2 has a 4.22:1 then later in the run changed to 3.89:1 - or so the rumors say.

The 3.89 to 4.22 would make about an 8% difference to speedo ready. My 67 to 60 is around 10 to 11% - but it's close. The current tyres on the car are 175/70R13 which are ever-so-slightly larger than the ones I calibrated for but it's not much (this should slightly counter the different diff.).

Back to diff. ratio. When I bought the Vogue it had been built from three donor cars. We know one of them was a Vogue Sports because I have the boot lid and badge, BUT, the Humber Vogue Sports never shipped as a Mk3 in Australia, so the boot lid is from a Mk2 - might the diff. be as well?
(The Sports did not sell as a Humber in Australia because all Mk3 Humber Vogues were upgraded to the Sports Alloy Head Rapier spec. motor - no need for a Sports.)

I'm very happy with a 4.22:1 final drive ratio - I had even considered chasing one up so that's good.
So a speedo software change is in the works.

How fast will it go?

The next question I get asked a lot is how fast will it go.
With my 3.89:1 differential, 185/65R13 tyres (that's tires to you USA guys) the motor will be doing about 4339 RPM at 120km/h. The motor is rated at 1465 RPM at 75% load and 50Hz. Since the controller will go up to 150Hz at it's most efficient switching rate (gets a bit complex here because it can actually go higher), then it follows that the motor can do 4395 RPM.
So it can go about 125 km/h.

How fast can it accelerate.
Another complex question. The peak power of the motor (around 70kW) is higher than the peak power my 45kW (peak) controller can deliver so initially the car will be controller limited. I have the parts to re-work my "other" controller to about 80kW so pretty much as soon as the car is safely debugged I will change over to the upgraded controller. They are physically identical - mounting, connections, everything.
The first graph is as it will go on the road, the second is with the upgraded controller.
To give these some perspective, the original Vogue did 0-100km/h in 17, 21 or 25 seconds - depending on where you get your information.

Thanks to "woody" from the AEVA forums for the extremely complex spreadsheet that takes everything - batteries, motor, controller, car Cd, weight, rolling resistance etc. - into consideration. Predictions from this spreadsheet have been verified on a real EV.

Range - or How far can you go on a charge?

I get asked a lot about the range of the car.
The calculations show the EVogue's projected range to be as shown in this graph.

A glossy brochure would advertise it as "Up to 160Km range". You can see that you would have to be driving at 20Km/h to get that far!
It turns out that the faster you go, the less far you can go. It has a lot to do with how "slippery" the car is when travelling through the air. The Vogue has no published figure for Cd (Coefficient of Drag) so it is yet to be determined (I have guessed at Cd = 0.45 and frontal area = 2m square).

These projections are based on flat and level driving with no start/stop and no hills so the real-world figures will be less. I'm estimating by about 15% but it will be very interesting to find out for sure. The hills don't matter too much as the motor will act as a generator (regenerative braking) when going down hills and even when stopping. In that way I get a large portion of the energy expended going up hills and accelerating, back again.

Weight Removed and to be Added

We went away for a 8 day holiday/break last week but now it's time to get stuck back into the EV.
The final weight of the car is pretty important. If it's too heavy I will have trouble getting VicRoads approval. So far it's looking good. About 10kg lighter than original.
The cells in beige are ones I haven't weighed yet or haven't made/purchased yet. Now what have I forgotten?