There,” Wedge, Small Bots.
• Hobbyweights — 1st “Rants Pants
(of Doom),” Wedge, Not So-Boring
Robots (Botrank #1); 2nd: “Igoo,”
spinner, Mad Scientist; 3rd: “Shake
Appeal,” spinner, EMF.
• Featherweight — 1st: “Gnome
Portal,” lifter, Robotic Hobbies; 2nd:
“Mangi,” spinner, Half Fast
Astronaut; 3rd: “Power of Metal,”
beater, EMF.
HORD Fall 2006 — This event was
held on 10/21/2006 in Omsted
Falls, OH. Results are as follows:
• Fleaweights — 1st: “Mr.
Bigglesworth,” saw, Udanis, 2nd:
“Low Lift.”
• Antweights — 1st: “Hit or Miss,”
saw, AC/DC; 2nd: “Fred Fred
Burger,” wedge, Udanis.
• Beetleweights — 1st: “D2,” drum,
D2; 2nd: “Chop Chop.”
Halloween Robot Terror — This
event was held on 10/28/2006
in Gilroy, CA. Results are as
follows:
• Fleaweights
— 1st:
“Change of
Heart,” wedge, Misfit; 2nd: “Atom
Bomb.”
• Antweights — 1st: “Fire Eagle,”
wedge, Missfit; 2nd: “Stumpy,” wedge,
DMV; 3rd: “Pooky,” wedge, ICE.
• Beetleweights — 1st: “Toe Poke,”
lifter, Kick-Me; 2nd: “Unknown
Avenger,” flipper, ICE; 3rd: “Itsa,”
spinner, Bad Bot. SV
TECHNICAL KN WLEDGE
Four Bar Lifters in Combat Robotics
● by Adam Wrigley
When it comes to flipping and
lifting weapons, four bar mechanisms are the crème of the crop. You’ve
seen them on TV or at your local
combat robot competition, and now
you want to know more about them. If
you’ve never seen one, take a look at
Figure 3 on the next page. The largest
benefit of the four bar design lies in its
ability to have any tip trajectory you
desire. You can lift an opponent nearly
straight up, or out and up, as seen in
Figure 1. The “out and up” motion is
what most people tend to use, and
allows you to actually tip over the
opposing robot. Simple lifters as seen
in Figure 2 tend to lift up and away,
causing the other robot to fall off the
tip before full extension is reached.
How Are They Powered?
There are a huge number of
different methods for powering a
four bar lifter. Electric motors can be
used along with several stages of
gear reduction to power either the
front or rear bar through torsion.
Linear actuators can be geared using
a rack and pinion method to
accomplish the same end result.
Other mechanisms include linear
actuators to nearly any part of any
bar or joint in the mechanism, or to
any bar through a pin/slot
technique. There really is no simple
way to explain the system. In fact,
there are entire college courses and
textbooks devoted solely to analyzing four bar mechanisms. To keep
this article shorter than a 400 page
textbook, I’ll simply concentrate on
four bar systems powered by torsion.
Torsion power is the simplest
method of powering a four bar, both
in construction and analysis.
Finding Input Torque
Now, we are looking at a four
bar mechanism with torque being
applied to either the front or rear
bar. What do we do now? We could
get an equation for the trajectory
based on the powered bar angle
input, do a force balance, and a
dynamic analysis. We could do that.
However, that isn’t really necessary.
The simplest way to solve this problem is to look at it as a work balance.
The work you put in the system will
equal the work you get out of the
system. The work you put into the
system is equal to:
Work = Torque * Angle
With angle being in radians
(radians = degrees * pi/180) and
equal to total angle traveled by the
input bar. The work output is:
FIGURE 1
FIGURE 2
Work = Weight * Height
where weight is the weight
of the opposing robot and
height is in the same units as
your torque (if you used
ft-lbs for torque, use ft for
30 SERVO 01.2007
