Subject:
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Heavily modified 8880 chassis, succesfully motorised and solar powered.
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Newsgroups:
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lugnet.technic
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Date:
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Fri, 31 Jan 2003 15:19:03 GMT
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Viewed:
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2145 times
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As a school project I'm building a small car powered by a solar panel. It
should come as no big surprise that I'm doing this with lego. :)
I started out with the 8880 chassis (without bodywork) motorised by an old
style 9V motor. The project is mostly about efficiency of course, so it
might not come across as the best choice for a car that has to run with very
little power. The solar panel is rather large though, (40x40cm or so) and
won't be on the car itself. I've measured it giving 5-6 watts, on a sunny
mid-winter (holland-) day. I decided to keep the gearbox, 4wd and
independent suspension, which many would also consider a 'wrong-choice' in
these circumstances. I want it to be as much like a 'real' car as possible.
I've taken out the 4 wheel steering for now though.
The basic design of the chassis is the same as the 'original' model. Some
prominent changes/features are:
-- vastly shortened wheelbase (8 studs shorter) (and I could easily make
it even shorter, loose more weight and make it faster...it would look very
odd though)
-- changed gear ratios (Gearbox-inputshaft/Wheels: 2/3 ; 1:1 ; 2:1 ; 3:1)
-- uses 7 gears and 2 axles less for the entire drivetrain than the original,
while retaining all the features.
-- all drive-axles are one-piece, no axle-joiners used. This makes the axles
stiffer and reduces friction.
-- 'neutral' suspension positing has the drive axles from the front and rear
diffs (with the u-joints) straight instead of bent down, to decrease friction
-- extra stiffening of the chassis to prevent it from bending, which prevents
the axles from twisting, which reduces friction.
-- All of the drivetrain is heavily lubricated with teflon. This greatly
reduces friction too of course...
-- I'm forcing 12 volts through the 9v motor.(It's connected to a 12volt HD
lead from inside my computer :D ) It will easily run with 9 volts too though.
-- Between the old-style 9v motor and the input shaft to the gearbox is a 9:1
reduction. (through 24 & 8 gears and through a string on a bush and on a
wedge-wheel. It runs even better when I replace the bush/string/wedge-wheel
reduction with gears)
-- The thing weighs roughly 900 grams right now. (bit more) Can still be
reduced a bit though, which not only makes it accelerate faster but also
puts less strain on the drive axles through the suspension and therefore
decreases friction some more.
I've got a slightly unfinished .ldr of the model;
http://home.wanadoo.nl/gillish/SC_8880.ldr . It lacks wheels and any
steering mechanism, but all the 'important design features' are in
it. The gearbox design has taken the most thought, even though it looks so
simple. Some screenshots here:
http://home.wanadoo.nl/gillish/solar_car_perspec.PNG
http://home.wanadoo.nl/gillish/solar_undertray.PNG
http://home.wanadoo.nl/gillish/sc_undertray_closeup.PNG
With the motor running on 12 volts, the first two gears are so short that
the car's topspeed is limited by the engine revs. That topspeed is reached
very quickly after starting from a standstill, and there's plenty of torque
to overcome (not too major)obstacles. In 3rd gear, the car goes much faster,
but it doesn't accelerate as fast. In 4th gear, the car goes yet faster but
of course it also takes a while to reach that speed. So long in fact, that I
haven't had it max out because my power cables are too short and my room is
too small. :D
I'm guessing it does about 5km/h with the motor on 12 volts in 3rd/4th gear.
The solar panel actually puts more volts on the engine (approx. 16) and
makes it run faster than when the motor's connected to a 12volts
powersource. Using the solar panel the car accelerates to what i would guess
at 8km/h or so. I haven't been able to test it much though.
I plan on getting a more efficient, non-lego electric motor(that's actually
ment to run at 16+ volts, unlike the lego motor ;) ), and coupled
with some spring/summer-sun I hope to reach atleast 10km/h and preferably
15km/h.
Tips to improve and opinions are very welcome.
Gillish
Oh, this is my first post on lugnet; Hi all. ;)
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