Subject:
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Re: Heavy load on LEGO chassis over uneven ground
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 11 Dec 2005 14:40:26 GMT
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Viewed:
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1576 times
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In lugnet.robotics, danny staple <orionrobots@gmail.com> wrote:
>
> If they can build bridges that can take a few something like 28-30
> kilos of weight, then handling a laptop is not impossible. It would
> really be a matter of doubling up load-bearing beams and supporting
> them with the right structure, being aware of weak points, and where a
> beam may bend or break. It is about making sure that there are
> multiple supports so that one pin is not left bearing it and gets
> sheared off. I really dont doubt that Lego can do this, but it is
> really a matter of the engineering. You might have to build it larger
> than you wanted, but it is doable.
>
> You might really have to do your home work on load bearing structures,
> bridges, lattices and techniques to take the force away from
> troublesome hotspots. I look forward to seeing it. I have been
> considering building a Lego bot chassis around an SBC for a while, but
> not entirely sure what to do with the power supply yet.
> --
> Danny Staple MBCS
> OrionRobots
> http://orionrobots.co.uk
> (Full contact details available through website)
Another thing to consider when carrying so much weight is the gear ratio and
motor power required. An under-powered robot with excess shaft friction will
not drive in a straight line! I built a strong robot chassis a few years ago
using 12V train motors for power, since at that time they were the most powerful
LEGO motors.
Underneath a 12V train motor, put two 16L beams with tiles on top. Then put an
axle through them at a point between teh train wheels and put 2 24mm pulleys on
each side with a 2L gap between the beams. Use the clips on the ends of the
motor to attach it to the beams with 4L beams and 2 layers of plates (then
strengthen vertically). Then put belts from each train wheel to each pulley.
The result is 8W of power on an axle at a speed slightly less than the motor
speed. Gear this axle down by 24:8 doubled up and use an 82mm motorbike wheel.
Double this up to make a tank-steered robot.
The next part is how to support the robot with all that weight and still turn,
also considering uneven surfaces and keeping all the wheels on the ground. Use
two swivel bogies on parallelogram suspension, one at each end, with the
parallelograms coupled with a shaft so that they raise and lower together. I
used 4L liftarms for the diagonal sides of the parallelograms, since they have
cross axle holes. Then put the heavy motor batteries half on each bogie to keep
them on the ground (I needed lead-acid batteries for my previous robot computer
card, so this seemed an ideal solution, using the weight to stop the robot
tipping). I used model team wheels for the bogies because they run free on the
axle, so no skidding occurs.
The robot will now have plenty of power and be able to travel over a changing
slope without any of the wheels leaving the ground. The only element left to
build is the power H-bridges for driving the motors. This would still be the
case with the new RC Car motors, since an RCX doesn't have the power to drive
them. The H-bridges I built at university were OK but probably not the most
efficient design. However, they did fit in a small space.
I'll have to see if I can get the photos of the robot scanned in as it was quite
a few years ago.
Mark
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Message is in Reply To:
 | | Re: How much weight can a LEGO chassis carry around?
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| If they can build bridges that can take a few something like 28-30 kilos of weight, then handling a laptop is not impossible. It would really be a matter of doubling up load-bearing beams and supporting them with the right structure, being aware of (...) (19 years ago, 10-Dec-05, to lugnet.robotics)
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