DRAW BRIDGE
Index
1.Introduction...1
2.Bridge parts...1
3.Parts construction...2
3.1.Wood base, plywood 7 mm thick, 30x10 cm...2
3.2.Secondary support (lath 2x1 cm cross-section) 5 cm high...2
3.3.Primary support (lath 2x1 cm de sección) 24 cm high...3
3.4.Pulley (made up of plywood de 4 mm thick or similar)...3
3.5.Assembly of the built parts...3
3.6.Electric circuit...4
3.7.Bridge (triangulated girders made with spaghetti)...5
3.8.Motor fixing...6
3.9.Views of the finished bridge...7
4. List of materials needed for each project ...8
1 Introduction
You are going to build a draw bridge with a triangulated girders structure on a wooden support. We´ll be able to raise/ lower the bridge by means of an electric motor controlled by a changeover switch.
2 Bridge parts
3 Making the parts
We will build the parts in the same order as follows:
3.2.
Secondary structure (lath 2 x 1 cm cross-section) 5 cm
high
3.2.1. 2 Pillars 4 cm high 3.2.2. A girder 7 cm long
3.3.
Primary structure (lath 2 x 1 cm cross-section) 24 cm high
3.3.1. 2 Pillars 23 cm high. With a hole 5 mm diameter 5,5 cm from the bottom
3.3.2. A girder 8 cm long leaning on the two pillars
3.3.3. A girder 6 cm long between the two pillars 4 cm from the bottom.
3.3.4. 2 Brackets (laths 2 x 1 cm). Right-angled triangle shaped pieces of wood, made two by two from one square piece 2 cm side.
3.3.5. Closed-eye screw screwed on the upper girder, at the centre.
3.4.
Pulley (made up of plywood 4 mm thick or similar)
3.4.1. 2 big discs 72 mm diameter with a hole 6 mm diameter in the centre. 3.4.2. 1 small disc 62 mm diameter with a hole 6 mm diameter in the centre. 3.4.3. Elastic band 10 cm long.
3.4.4. Wooden axis 6 mm diameter and 10 cm long
3.4.5. Glue the three discs with the small in the middle and pass the axis through the hole in the center. Glue it all with wood glue.
3.4.6. String 50 cm long + 1 open-eye screw. Tie one end of the string to the axis, near the pulley, and tie the other end to the open-eye screw.
3.5. Assembly of the made parts.
a) We can start to assemble the parts we have already made on the base of the bridge. Start by gluing with wood glue or solid glue (with a glue gun) the secondary support on the marks drawn on the wooden base. Use the metallic carpenter´s square so that the glued structure is vertical. Then glue the primary support and finally glue the pulley supports. DON´T FORGET TO USE THE CARPENTER´S SQUARE!!
b) The glued structure can be seen in the pictures below. Don´t forget to glue the brackets to the pillars in both the primary and secondary structures.
a) 5 electric wires 15 cm long.
b) Motor + staple + washer + screw 10 mm long
c) Electric connector for two connections + screw 10 mm long
d) Changeover switch:
d.1) Wooden base 15 x 7 cm area and 1 cm thick
d.2) 4 headless nails 3 cm long. d.3) clothes peg.
d.4) Two tin plate stripes 1 x 4 cm d.5) Two connectors for 4,5 volts battery Ask the teacher how to connect the electric circuit wires. The following diagram may help you:
3.7. Bridge (spaghetti triangular girders)
a) It has a base, two sides and a ceiling.
b) Base 15 x 15 cm + a piece of cardboard same length glued on the spaghetti truss. c) Two sides 15 x 5 cm
d) Ceiling 15 x 5 cm
e) Cardboard brackets to reinforce the spaghetti nodes.
f) Drinking straw, 5 cm long
Changeover switch peg
Battery
g) Wooden axis, 4 mm diameter and 10 cm long
h) How to build the bridge:
• The four sides must be built separately: bas, two sides and ceiling. First, they must be drawn REAL SIZE with a pencil on graph paper and spaghetti should be glued on yhe drawing with carpenter's glue. BE VERY CAREFUL: JUST A DROP OF GLUE MUST BE PUT ON THE TRIANGLES' APICES! Let them dry and harden for 24 hours.
• Cut them out carefully and remove the four sides (spaghetti girders) off the pieces of paper they had been glued. VERY CAREFULLY.
• Glue a piece of cardboard on the base.
• Add two bracings: they are two spaghetti sticks diagonally glued to give stiffness to the bridge so that it doesn't become distorted.
Bridge, bottom side
Bridge, upper view Bracket
Bracket
Bracing
Bracing
Bracing
• Reinforce the spaghetti triangles nodes with small pieces of cardboard glued on them. These pieces are called brackets.
• Glue the straw ( it is the bridge´s hinge) with solid glue as you can see in the picture. • Assembly of the bridge: if everything has gone well we can mount the spaghetti bridge
on the support structures, passing an axis 4 mm diameter and 10 cm long through the holes made in the primary support and through the straw.
3.8.
Motor fixing
a) Finally the staple that holds the motor in place must be placed like this: making sure that the elastic band is coupled to the motor axis and pulley, move the staple placing to the point that the elastic band is slightly stretched. Mark with a pencil the position of the staple on the wooden base and hold it in place with a screw and washer.
3.9.
Views of the finished bridge
Axis 4 mm diameter and 10 mm long
4. Project materials list
Material
Amount for each project
Total (x 60)
Washer 1 60
Solid glue rods 1 kg 1 kg
Electric wire 15 cm x 5 pieces = 75 cm It´s in the workshop Cardboard 1 sheet (supplied by the
students)
60 Headless nails 3 cm long 4 240
Electric connector 2 120
Carpenter's glue 1 bottle 1 bottle 4,5 volts battery connections 2 120
String 50 cm 30 m
Wooden axis 4 mm ᴓ 10 cm 6 m Wooden axis 6 mm ᴓ 10 cm 6 m Elastic band 10 cm long 1 60
Motor staple 1 60
Open-eye screw 1 60
Closed-eye screw 1 60
Plywood sheet 4 or 7 mm thick (bridge base)
30 x 10 cm + 8x8 + 8x8 + 8x8 (3 discs) = 30x10 cm + remnants
It´s in the workshop
Motor 1 60
Drinking straw 5 cm (half a straw) 30 Clothes peg 1 (supplied by the students) 60
Spaghetti 1 pack 1 pack
Tin stripes 1 x 4 cm (2 stripes) It´s in the workshop
