Science, technology, engineering, and math building a trebuchet

6 Pages·0.349 MB·English

by  Eldridge Patsy.

S T E M
cience,
  echnology,
  ngineering,
 and
  ath

Building
 a
 Trebuchet

Trebuchet
 parameters

1. Your
 completed
 trebuchet
 must
 fit
 in
 a
 copy
 paper
 box,
 with
 the
 lid
 on,
 when
 the

machine
 is
 in
 the
 pre-­‐launch
 position
 as
 shown
 below.

2. Your
 projectile
 will
 be
 a
 5-­‐gram
 ball
 of
 clay.

 You
 must
 hurl
 the
 clay
 a
 distance
 of
 at

least
 1
 meter.

These
 ratios
 and
 dimensions
 are
 a
 good
 starting
 point
 for
 your
 design:

Ratio
 of
 counterweight
 mass
 to
 projectile
 mass:
  100:1

Ratio
 of
 throwing
 arm
 length
 to
 counterweight
 arm
 length:

 4
 or
 5:
 1

Sling
 length
 =
 throwing
 arm
 length

Pin
 angle
 =
 30
 degrees

DESIGN
1.
 Come
 up
 with
 a
 dimensional
 plan
 by
 filling
 in
 possible
 lengths
 and
 masses
 on
 the

diagram.
 Keep
 in
 mind
 that
 the
 final
 trebuchet
 must
 fit
 in
 a
 copy
 paper
 box
 with
 the
 lid
 on

(in
 pre-­‐launch
 position).
2.
 Estimate
 the
 range
 of
 your
 projectile
 to
 be
 sure
 it
 will
 go
 at
 least
 1
 meter.
 You
 can
 use
 a

simplified
 formula
 that
 assumes,
 among
 other
 things,
 100%
 efficiency,
 and
 a
 perfect
 45-­‐
degree
 launch
 angle:

m
estimated range = 2 1 h
m
2
m = mass of counterweight

1
m = mass of projectile
2
h= height of counterweight above its lowest point

Note:
 Because
 the
 trebuchet’s
 efficiency
 will
 be
 much
 less
 than
 100%,
 you
 might
 want
 to

divide
 the
 estimated
 range
 by
 2
 for
 a
 conservative
 range
 estimate.

PROTOTYPE
3.

 Use
 your
 initial
 plan
 to
 build
 your
 prototype.

TEST
4.
 Test
 your
 prototype.
 How
 far
 does
 it
 hurl
 the
 clay
 ball?
 How
 does
 that
 compare
 to
 your

estimate?
 If
 it
 doesn’t
 work
 properly,
 what
 needs
 to
 be
 fixed?

5.
 Make
 necessary
 adjustments
 and
 changes.

EVALUATE
6.
 Sketch
 a
 final
 dimensional
 diagram,
 labeling
 all
 lengths
 and
 masses.

7.
 HURL!
 Operate
 your
 trebuchet
 three
 times,
 measure
 the
 range
 of
 your
 projectile
 for
 each

hurl,
 and
 find
 the
 mean
 range.

Trebuchet
 Competition

 Longest
 mean
 range
 (first,
 second,
 third
 places)

 Longest
 single
 hurl

 Best
 accuracy
 (place
 your
 trebuchet
 and
 hit
 a
 fixed
 target)

 Greatest
 precision
 (least
 range
 variation
 in
 3
 hurls)

STEM Project
Building a Trebuchet
Patsy Eldridge
June 10, 2011
CPO Science

Building a Trebuchet, Page 1
Materials
An ordinary can of toy construction materials plus a few additional
everyday items can be used to build a trebuchet.
Each team of 2 - 3 teachers will need a copy paper box (with lid)
that contains:
•1 can of toy construction materials (small 66-piece set is great)
• Duct tape
•String
•Assorted (very small) washers, screws, nails, eye hooks
•Heavy duty wire coat hanger (not the cheapie)
•CPO weights and plastic marbles (they don’t have to be in the box!)
Tools to have on hand for teachers to share:
•small pliers
•small hammer
•small phillips head screwdriver
•scissors
CPO Science

Building a Trebuchet, Page 2
How it works
One end of the sling string is
taped to the side of the
throwing arm. The other string
is tied to a washer and slipped
over the bent coat hanger pin
as shown.
Push the beam down to the
tabletop. The heavy
counterweight will resist
this motion, so be careful!
The plastic marble sits in
the little duct tape sling.
Arrange the sling neatly,
get out of the way, and
hurl!
CPO Science

Building a Trebuchet, Page 3