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In lugnet.robotics.rcx.legos, Elizabeth Mabrey wrote:
> Hi ,
>
> According to the http://www.fifth-r.com/cssoh1/actest.htm, a
> mini-compressor (using a single small pump) is actually more efficient than
> using double pump. It said more efficient, but not generate higher output
> though, correct???
Good reasearch..... Using the mindstorm motors, who's torque is a good match
for the small pump, the small pump gets to a static pressure faster than a large
pump using hte same kind of motor.
The small pump does not keep up with the total throughput of a large pump
compressor though, presuming the minimum required pressure for a circuit is
acheiveable with the large pump and mindstorms motor.
>
> http://www.fifth-r.com/cssoh1/compress/compdisc.htm produces a more
> persuasive test. However, it is not motorized. I wondered if there is
> anyone who has done a comparison the acculumative power output in a more
> extended period of time, say merely 30 seconds or so...
Fair question. I think it is time that I do that.
I have to come up with a benchmark to test the performance of individual small
pumps, because I think I have some that have marginal seals.
I'm also working on an apples and apples comparison.
It takes six compressions of a small pump to equal one compression of a large
pump. I'm working on a dual - six small pump design (12 pumps) that will be
geared down exactly like my large dual pump design, to see which performs
better.
By using the same motors, same power, and same compression volume, we can do a
fair comparison of large versus small.
Despite all my years of being in the large pump compressor camp, I think there
is a high possibility that the small pump will win. I think this is true
because the work needed to compress a single small pump is smaller than a single
large pump. With the small pumps, you can evenly distribute the compressions
through a full 360 degree rotation, leaving you with 60 degree seperation for
six small pumps. Given that, the motor does not have to work as hard at any
gien point in time for small pumps.
I'm trudging along in this analysis.
>
>
> Reponding to Kevin:
> >
> > Will your car have a pneumatic engine?
> Yes, I also want pneumatic steering.
>
> > The large pump can run the engine with no externally
> > controlled switches.
> >
> > Steering on the other hand would require control of two switches.
>
> >
> > Both pistons expanded could turn right. Both pistons
> > contracted could turn left. One expanded and one contracted
> > would go straight ahead.
>
> I don't quite understand this... But again, I am a newbie, I should read on
> the pneumatic info first before I ask too many questions.
Questions are fine. I enjoy them!
I guess it depends on how you are going to use the pumps, switches and pistons.
Typical pneumatic circuits run with a relatively static pressure. This makes
pistons fully expand or fully contract. When pressure goes into a switch, and
the outputs hooked to a piston, the piston either opens or closes. There is
typically no middle ground.
To achieve steering given this sort of binary environment, one piston could give
you two steering positions (for example turning right or turning left, or
straight ahead and turning).
To achieve three steering positions (left, center and right), you need to be
able to acheive three stable pnuematic states. To do this you can use two
pistons. Lets think of it mathematically. If we give a value of 1 to an
expanded piston, and zero to a contracted piston, we can set up a formula to
describe how the pistons interact (presuming they are hooked together at their
bases......) Lets use this formula.
length = piston1length + piston2length
Given the above formula and all possible combinations of piston1length and
piston2length we get this table.
0 + 0 = 0
0 + 1 = 1
1 + 0 = 1
1 + 1 = 2
There are three possible total lengths (0, 1, and 2). If we assign length 1 to
going straight ahead, then 0 could be considered turning left, and 2 considered
turning right.
The above may not be what you are thinking about at all. You could be thinking
about a more analog situation...... hook two pistons to each other with one
piston expanded and the other contracted. Now when you contract the expanded
piston, it makes the contracted piston expand. If you only contract it half
way, the other piston only expands half way.
This could be done, but the problem is that over time, leakage can change the
total volume of air in the closed system, and cause steering bias problems.
Kevin
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Message is in Reply To:
 | | RE: lego pneumatic
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| Hi , According to the (URL) a mini-compressor (using a single small pump) is actually more efficient than using double pump. It said more efficient, but not generate higher output though, correct??? (URL) produces a more persuasive test. However, (...) (20 years ago, 9-Jun-04, to lugnet.robotics.rcx.legos, lugnet.technic)
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