Subject:
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Re: 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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Sat, 15 Feb 2003 22:16:17 GMT
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Viewed:
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2371 times
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In lugnet.technic, Rob Stehlik writes:
> > I'd have to connect the 2 motors in serial
>
> ??? Why would you do this? I'm not an electronics expert, but connecting
> motors in series seems strange. The speed of a motor is proportional to the
> voltage across it, so I think you would get drastic speed variations between
> two motors in series. This was discussed on the newsgroup a while ago:
> http://news.lugnet.com/robotics/?n=19878
> Someone actually tried connecting two motors in series (it is possible with
> Lego, just a bit awkward) and this is what he found:
> http://news.lugnet.com/robotics/?n=19880
> If you connect two motors in parallel, they have the same voltage across
> them, so their speed should be much more closely matched. I guess they draw
> more current in this case, but such is life...
>
> > Connecting two motors without a diff
> > is do-able, but in serial, one of the motors will probably get more voltage
> > than the other, which makes the 'tandem connection' less optimal.
>
> Right. In parallel this won't be a problem.
Connecting the motors in parallel means they'll get 16volts at about .25amps
each. (if their combined electrical resistance is right, which it isn't,
which makes the solar panel perform badly...) That's 4 watts per motor, when
they're intended to run on 1.1 watts...I'll still be overloading them.
They'll be overloaded in serial too, but only with current, not
voltage...Which I'd guess is the lesser evil.
The point is I have over 9 watts at my disposal from the solar panel, and I
don't want to waste that...Lego motors are simply not powerful enough unless
I use a whole lot of 'm together, which brings too many other new problems
along, and the price advantage will diminish when I'm going to buy like 6
anyway...(which would still only be rated to use 6.6 watts)
I'd really rather shell out the money and get a 'proper' motor that's ment
to be using this kind of power, and does it more efficiently too. The motor
I'm looking to buy will be able to produce 1.3 - 1.4NCm of torque at
5700RPM, which is 8 watts of mechanical power. (!) I'm not going to even get
close to that with lego motors unfortunately...
>
> > You're totally right about the weight though. The motor I'm looking to buy
> > weighs in at some 160grams, much more than 2 lego motors.
>
> And don't forget cost :)
>
> Actually, if your main focus is efficiency, why would you even use the
> supercar chassis to begin with? I think you could increase your efficiency
> dramatically just by using a highly simplified chassis with minimal gears
> and parts. It would be lighter and have less losses due to friction.
>
> Rob
I could of course just take two beams, two axles, four(or even 3) wheels, a
motor and a pulley, but what's the fun in that? I'd like to build something
that somewhat resembles a 'real' car. That's why I want to keep the 4 wheel
drive, 4 speed gearbox, independent suspension and large rubber tyres. And,
if I'd build a car so simple and light, it would go too fast, meaning the
power line from the solar panel to the car has to be dragged along very far,
forcing me to put the solar panel on the car itself, slowing it down again...
I've got a chassis weighing 900 grams now with lots of features, that runs
very smooth (thanks to lubricant and smart design), now all I need is a
proper motor to power it.
I've also changed the gearbox design again today, made some major changes.
Now it uses yet another gear less (now 8 less than the original 8880) and it
runs yet smoother. Additionally, it's lighter too. I think I'll upload an
updated .ldr tomorrow.
I'm sorry if I sound harsh sometimes, I just have a clear image of what I
want to do and how to get there...
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