Discover: Discover: Learning about: Cams & Cranks Learning about: Cams & Cranks What is a crank mechanism? What is the relationship between a crank’s Crank as a handle What is the relationship between the Relation of force and speed position and the difficulty in rotation? You have probably seen different cranks on a variety of devices: handle position, the force applied and the The use of a crank as a handle, even though it has many What is the relationship between the force from the old style pencil sharpener, the simple kitchen meat lifting speed? applications, it does not take advantage of the full potential of (difficulty in rotation) and the speed? grinder to a boat winch that winds up the rope to lift the sails. the mechanism. However, the oil drilling machine (pumpjack) But, how does a crank actually work and what can it offer us? uses cranks not as handles, but as parts of the entire drilling Level Of Difficulty Level Of Difficulty Discover all these by following the instructions below. mechanism. How? Let’s build the next model and find out!

1. Tick the correct boxes in the following table comparing the 1. Complete the following table with your measurements and Materials Needed: Materials Needed: force applied on the crank in order for the load to be totally compare the force and speed for each case. - Engino® Simple Machines (STEM40) or Cams - Engino® Simple Machines (STEM40) or Cams lifted, as well as the lifting speed. & Cranks (STEM04) or Master Set (STEM50). & Cranks (STEM04) or Master Set (STEM50). Piston’s Force Piston’s Pump Speed Ηandle’s (difficulty in rotation) - Ruler. Case pump Force Lifting Speed Position Ηandle’s (difficulty in rotation) distance Easy Medium Difficult Slow Medium Fast Case Position Easy Medium Difficult Slow Medium Fast Procedure: Procedure: 1. Find the instructions in pages 21-22 and 1. Find the instructions in pages 23-24 and 1. 5 cm build the fishing crane model. 1. build the oil drill model.

2. You will need to tie and wrap the string on 2. In this model, there are two cranks: the 2. 3 cm the pulley a few times so it works properly. 2. input and the output. Identify them and write their names in the picture at the bottom. 3. For each case we are going to change the 3. 1.5 cm position of the handle (as indicated in the 3. For case 1, the middle axle is inserted in 3. picture below). For case 1 the handle is the first hole of both the output and the already positioned in the first hole. Turn the supporting cranks (see number 1 in the 2. Look carefully at the “Handle’s position” column and the crank and feel the force applied in order for picture below). Turn the input crank, feeling “Piston’s pump distance” column and write down your the load to be lifted and also observe the 2. Look carefully at the “handle’s position” column, the “FORCE” the force applied and observing the speed of conclusions about the relationship between the position of the lifting speed. column and the “LIFTING SPEED” column. Write down your the piston pump. Then, with the help of a handle and the distance the piston pump travels. conclusions about the relationship between the position of the ruler, measure the maximum distance which 1 3 axle on the crank, the difficulty in rotation and the speed by the piston pump is moving along the vertical The further away the handle is from the axle, the longer the distance which the load is lifted. axis (simulated by the extendable rod). travelled by the piston pump (and vice versa). The further away the handle is placed from the axle, the easier it 2 gets to turn the crank. However, the load is lifted slower because the 2 4. Move the handle one hole closer to the covered distance becomes longer (bigger circle). 3. Now, write down your conclusions about the relationship 3 axis (case 2). Turn the crank, making sure between the difficulty in turning the crank (“Force”) and the that you keep the same rotating pace with speed of the piston pump. 3. Complete the following sentence using the words in the 1 your hand as before. Feel the force and box. The further away the handle is from the axle, the easier the crank observe the lifting speed again. 4. For case 2, insert the middle axle in the second hole of the cranks (indicated with turns and the faster the piston pump moves (and vice versa). axle, easier, smaller, more difficult, crank, pulley, 5. Finally repeat the same procedure for number 2) and turn the input crank. Repeat longer, manually, faster, slower case 3 and complete the table on the right. the same observations (speed, force and distance). Note that the extendable rod is not manually crank When we ...... turn a ...... using our fully inserted in now, so measure the maximum travel distance accordingly. axle hand, the further away the handle is from the ...... output crank 5. For case 3, remove the middle axle and the ...... easier it is for the crank to turn, but the load is insert it in the third hole of the cranks lifted in ...... slower pace. (indicated with number 3) and follow the same procedure as before. Again, be careful piston pump input crank when taking your measurement, by placing your ruler at the appropriate point.

Engino® “fishing crane” model Engino® “oil drill” model 15 16 Discover: Learning about: Cams & Cranks What is a cam? Quiz Cam profiles Which are the major types of cams? In ancient years, craftsmen in Egypt, Greece and Rome created What are rotational and reciprocating many moving figures as toys, which were manually operated. motions? Exercise 1 These devices were called automata meaning “acting of one's own will”! See how you can convert a simple toy model to a real Complete the boxes using the words from the box (2 points) Level Of Difficulty automata machine! Note that we will use Engino pulleys as cams. guides

1. In the following picture, Materials Needed: output motion: cam, follower, guides, identify the type of input - Engino® Simple Machines (STEM40) or Cams stroke, shaft and output motion and reciprocating & Cranks (STEM04) or Master Set (STEM50). write them in the boxes. follower - Ruler. Choose between reciprocating motion stroke and rotational motion. Procedure: Also, indicate both 1. Find the instructions in pages 25-26 and shaft motions with arrows. build the moving figure model. Turn the cam crank and observe what happens. Use a ruler input motion: to measure the maximum elevation of the Figure max 2.7 figure and complete exercise 1. rotational elevation: ...... cm

2. Remove the medium pulley from the black 2. When you insert the black axle in the centered hole of the axle and reassemble it with the black axle medium pulley, what do you observe when the crank is turned? Exercise 2 passing through the hole in the center. Write The figure does not move because the axle is not placed in an offset Can you identify the basic parts of a steam machine? Complete the boxes using the appropriate words from the your observations in question 2. box (2 points) distance. 3. Remove the medium pulley from the black axle and replace it with the big pulley. Insert 3. How much is the maximum elevation if we use the large connecting rod the axle in one of the four holes around its pulley? Compare it with the one of the medium pulley (question center. Measure the elevation of the figure 1) and explain your findings. flywheel and compare it with the one from the The max elevation is the same as the medium pulley (2,7 cm), connecting rod, cam, piston, medium pulley. Complete exercise 3. because the offset from the centre is the same in both cases. crank, crown, flywheel, torque 4. Remove the big pulley and assemble the two pulleys together as shown here. 4. How does the figure move when the cam assembly of step 4 is used as compared with the single cam assembly above? crank piston The single cam assembly provides a continuous reciprocal motion. The pear-shaped assembly provides a dwell period and the figure moves in reciprocal for a short period of the cam’s revolution. Exercise 3

5. In the figures below we see different types of cams. Write Correct the following paragraph on cranks by circling the correct word in each case (2 points) their names below using the ones from the box. 5. Put this assembly in the appropriate drop cam, triangular cam, round cam, heart-shaped cam The first use of a crank was as a lever / handle in order to rotate / lift things, achieving rotational / lifting position by inserting the black axle in the center hole of the big pulley. Turn the crank motion. The crank is a device / mechanism used to convert lifting / rotational motion to reciprocal / and observe the motion of the figure. rotational, as we have observed in the oil drill model. In order to turn the crank easily, its handle / pulley should Complete exercises 4 and 5. be positioned far away from / near to the axle that produces the output movement. 6. You can play more with the figure! Place the big pulley on top (as a head) and draw a guitar in a piece of carton and place it on its round cam triangular cam drop cam heart-shaped hands to create a guitarist! cam 17 18 Exercise 4 Exercise 6

Join the names of cam profiles with the correct pictures (indicated with numbers) (3 points) A pepper grinder’s crank has a radius (R) of 3 cm and a force (F) of 20 N* is applied on it. Can you calculate the Torque (T) created on the pepper grinder? (3 points)

The formula for Torque is T = R x F, where R is the distance R 1 triangular cam 4 from the center of the crank to the point where force (F) is F drop or snail cam applied. But before we use it, we need to convert all units in

SI system: pepper grinder round cam

2 5 R = 3 cm = 0.03 m F = 20 N *Newton (N) is the unit of measurement of force heart-shaped cam T = R x F = 0.03 x 20 _ T = 0.6 Nm Newton meters (Nm) is the unit of measure of Torque

linear cam

pear- or egg Exercise 7 3 shaped cam 6 The following pictures demonstrate some examples of different types of motion: reciprocal, linear, oscillating and rotational motion. Can you identify them and write them correctly under each picture? (3 points)

Exercise 5

Do you know the cam terminology? Put the correct names in each box (3 points) Newton’s Helicopter’s A saw An injection An exercising wheel Car window cradle propeller for hamsters wiper

follower, fall, stroke, direction of rotation, rise, dwell oscillating rotational reciprocal linear rotational oscillating

follower Exercise 8 Can you complete the names of the different types of followers found in the box? (2 points)

offset follower, roller follower, flat follower, point-knife follower stroke fall rise

direction of rotation flat follower point-knife follower roller follower offset follower

dwell Visit our online resources to find the solutions of all the activities: www.engino.com/solutions/stem04

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