I had a good look at the Kormilda car today, and had a good chat with their electrical guy, the same guy who designed the NTU motor (now NGM). It seems only part of the car was built by the school, and most of it is parts of the 1993&1999 Desert Rose cars.
Kormilda College's "Towards Tomorrow" from 2005Specs:
Array: 1200W mono silicon UNSW topcell 16% 8m^2 rectangle
MPPT: NTU - lots!
Battery: 48V 55AH, deep cycle lead acid, 90kg
Motor: Original NTU motor (NGM prototype)
Controller: Original NTU controller
Weight: Approx 290 kg incl batteries
Cda: 0.14 (1999)
Chassis: Aluminium spaceframe
Body: Fibreglass over foam
Wheels: 2 front, 1 rear
Tyres: Moped, with tread. 16" rim
Front suspension: Mcpherson struts
Rear suspension: Double sided swingarm
Brakes: Custom hydrollic callipers on all wheels, front operated by peddal, rear by hand lever
Throttle: Torque control knob plus power boost override button. Brake cutoff. No self returning peddel or lever.
Telemetry: Lots of keen students, a radio, voltmeter and battery ammeter.
Rear view: camera
Wheel covers: Originally turning spats on suspension. Does not fit new tyres, so may run without covers, or with makeshift fixed covers.
Very interesting car!
ReplyDeleteIt will be interesting to see how race strategy is influenced by the cycle efficiency of the lead-acid batteries.
Will you be able to deduce the rolling resistance of the moped tyres from race data?
BTW "hydraulic" "pedal" LOL!
Keep up the good work!
Barry.
Hi again,
ReplyDeleteI have just been thinking about the battery efficiency thing.
It seems to me that the difference in car efficiency between good 1-sun conditions and poor-sun conditions will be more noticable with the lead-acid batteries and the relatively low bus voltage (and thus higher current).
Running purely on PV in good sun the car looks like it will be great, but running purely on battery you are looking at roughly 1/3C to 1/2C discharge rate and the battery won't like that much! Throw in Hayes Creek Hill coupled with a poor-sun condition and you are looking at way over 1C discharge and things will get really interesting!
I remember, at 1C, the watt-hours on my lead-acid batteries drop to about half of the 1/20C rating.
Obviously, you will be aware of all of this, but I am just relating this in my own mind to our "Was that Hayes Creek Hill?" / no telemetry situation in the 2007 race.
Like I said, I think the race strategy is going to be really interesting with this car.
Be kind to your battery!
Wishing you lots of sun on the hills...
Barry.
Just catching up with comments..
ReplyDeleteIt will be interesting to see the cycle efficiency of the lead acids. As it happends I've been nominated as strategist, so that will be fun! The strategy is fairly simple: The array can fully charge the battery in the evening and morning, especially as the team usually stops early to get a good camp site. This means we drive to discharge the pack 90% each day, while maintaining a roughly constant speed. The only info I have is battery voltage and battery current. The students report and log the battery current and voltage every few minutes, and I add up the amp hours. The car only runs on cruise control, constant torque like Solar Fern. The previous stategist will be with us for the first two days, so I'll get an idea of the car's performance. Of course if theres bad weather expect in the evening we need to conserve the battery for the next morning.
The other guy will be doing strategy for Hayes creek hill, so it will be interesting to see how he does it. We probably wont be going up very fast, so it could be a grunt! I'd just double the current figures for adding up amp hours, more if it's really high current. Will be interesting. The car does not have a very high throttle position, just flat cruise range, then the turbo button for hills, starting etc. Will need some run up.
The tyres are Michelin M45 moped tyres, 16" x 3.25", on 2.15" rins. I've seen other teams running the new Michelin solar car tyres on 2.15" rims, but not top teams. I'm hoping to do some tests on the track to demonstrate rolling resistance to the students, could be interesting, but the students are only there after school so there may not be time. During the race there might be opportunities, who knows. We will at least get some idea of power vs speed, although the array must be off to measure motor current.