Subject:
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Pneumatic steering (was Re: Suspension)
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Newsgroups:
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lugnet.technic
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Date:
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Sun, 3 Apr 2005 17:27:10 GMT
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Viewed:
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4003 times
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I am currently trying to build a vehicle with pneumatic steering.
Pneumatic steering:
* If you move the lever on your control-unit slightly to the left/right, the
vehicle will make a wide turn left/right.
* If you move the lever on your
control-unit completely to the left/right, the vehicle will make a short turn
left/right.
* If you release the lever (bring it back in center position), the
vehicle moves straight forward again.
This doesn’t happen with Lego models
(e.g. the distance guided vehicle from set 8082). If you want this vehicle to
move straight forward again, you have to move the lever in the opposite
direction first (and bring it back in neutral at the correct moment).
I
accidentally ran into this LUGNET-post:
In lugnet.technic, Mark Bellis wrote:
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With Lego pneumatic parts it would be different from the real thing, since
Lego cylinders are to coarse in operation, with to much friction to be able to
stop accurately at a given position with a given air pressure.
However, the way to do it would be to set a pneumatic valve to switch at the
correct point. I have successfully got a pair of cylinders to stop in the
middle of their travel, the application being pneumatic steering for a JCB.
My steering system uses a pair of valves to command the position (left, right
or centre), with three valves being
connected to the cylinders. I use antennas as stoppers in some tubes, one on
each of the outer valves in a line of 3. The 3 valves have their levers
offset in order to switch at different points.
The idea is to apply pressure to both sides of the cylinders equally at the
correct height, but if the cylinder is displaced either way by a small amount
the pressure to one end will cut off and it will self-centre again. In the
centre the middle valve is in its centre off position, but both outer valves
are just on. Moving either way one of the outer valves cuts off and moving
further the centre valve opens.
The steering system works best when moving from one end to the centre, rather
than from a slight offset to the centre, due to the friction.
Mark
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Unfortunately, there’s no picture with this post.
I slightly simplified this theory and came up with this:
If you
move the lever on the control-unit to the left/right, the pumps will go
left/right until the second valve is actuated. As long as you keep the lever to
the left/right, the pumps will stay in this position. Once you bring the lever
back in neutral position the pumps will move right/left until the second valve
is also back in neutral position (it doesn’t stop exactly in the middle, but it
comes pretty close).
But this does not solve my problem: I want the pumps to
stop in any possible position (the further the lever goes, the further the
pumps go).
And then I came up with this:
Moving
the first one to the left will cause the second one to move to the left too. It
works well with short hoses, but it gets tricky if you use longer hoses (I want
to hold my control-unit at least at 1.5m distance).
Because LEGO doesn’t have
one-way-valves (yet), I need two seperate input-lines to prevent air from
flowing from one line to the other (with a no-pressure situation as a result).
This would require two “pressure valves” (as seen in Jennifer Clarke’s
control-unit) and a very big control-unit.
However, there’s another problem:
every now and then I hear a “PFWT” (air escapes through one of the valves) and
both cylinders are no longer aligned. Re-aligning is done best if both cylinders
are in outer position, so I have to pick up the vehicle every time this happens
(and it happens too often in my opinion...).
Anyone out there working on
something similar but with better results so far??
Maarten
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Message has 1 Reply:
 | | Re: Pneumatic steering (was Re: Suspension)
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| (...) The ways to get round your last issues are: Use flex tubing for most of the long tubes - this eliminates the balloon effect. You can get one-way valves from Big Ben Bricks: (URL) With sudden movements you will still get air escaping though. (...) (19 years ago, 3-Apr-05, to lugnet.technic, FTX)
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Message is in Reply To:
| | Re: Suspension
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| (...) With Lego pneumatic parts it would be different from the real thing, since Lego cylinders are to coarse in operation, with to much friction to be able to stop accurately at a given position with a given air pressure. However, the way to do it (...) (20 years ago, 17-Aug-04, to lugnet.technic)
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