Retro Mechanics

The Electric Motor

A motor is a possible drive for a machine. There are two types of motors: the combustion motor and the electric motor. For example, a car is driven by a combustion motor. Of course, you don't have such a complicated motor in your construction kit, but you do have an electric motor, which we will call the E-motor for short.

Electric motors are the drives for most of the everyday machines. They can be used everywhere where electrical energy is available. The electric motor in your construction kit has a very high number of revolutions per minute (RPM), which means that it rotates so fast that you cannot even see one single revolution. But your motor is very ”weak,” which means that it cannot lift loads and cannot drive any vehicle. To reduce the revolutions and the make the motor ”stronger,” you need a gear unit.

Worm Gear Pair

A worm gear pair is best suited to reduce the high RPM of the motor. To do this, a worm gear is placed on the motor shaft, that is the rod, which extends out of the motor casing. The worm gear drives a toothed gear.

This type of gear unit is used where high revolutions per minute are to be reduced in a small area. A worm gear pair works in a self-locking manner, which means that the worm gear can be driven by the worm gear pair, but on the other hand it locks the gear unit.

Worm Gear Pair in a Bar

Bars and cranes use this gear unit because here the safe locking of the worm gear keeps the bar or the attached load from ”reversing” the drive.

 

Your task:

1. Build a copy of the bar model.
2. Rotate the bar upwards with the crank. How many times do you have to turn the crank to put the bar in a vertical position?
3. Try to pull the bar downwards with your fingers. What happens?

Of course, you had to turn the crank a few times to move the bar 90°. Were you able to pull the bar down?
See, this is how a self-locking gear unit works. With the small crank, you could easily lift the big bar so you increased the driving force with the worm gear pair.

The worm gear pair has many advantages:

• It saves space.
• It reduces the revolutions per minute of the drive many times.
• It is irreversible.
• It increases the force of the drive.
• But, it also changes the direction of the rotational movement by 90°.

Turntable

The mechanism of the worm gear is used in many machines. A simple example of this is the turntable, your next model.
For this model, the revolutions per minute will be reduced and the direction of rotation will be changed. The resistance of the loaded turntable must not stop the motor. 

 

Your task:

• Build a copy of the turntable.
• Put a pot with water or earth in it on the turntable plate, of course only a pot that fits on the plate.
• Can the little motor really rotate the big pot?

Your task:

• Build a copy of the crank gear 1.
• Turn the crank one time. How many times does the shaft with the second toothed wheel turn?
• Turn the crank clockwise. What direction does the driven gear turn and so the second shaft?

If you want to move a vehicle in this way, you would move very slowly. Also, you would go backwards. This model is only to show you how to build a simple gear unit and make calculations for the gear unit.

Your task:

• Build a copy of the crank gear 2.
• Turn the crank one time. How many times does the shaft with the second toothed wheel turn?
• Turn the crank clockwise. What direction does the driven gear turn and so the second shaft?

If you would move a vehicle in this way, you would move somewhat faster than with your first model. Calculate the transmission ratio for this gear unit as well.

 

Toothed Gearing with Chains

If there is a greater distance between two shafts, then a tension gear unit is used to span this distance. Belts or chains are used as a tension medium. They connect the drive gear and the driven gear over longer distances with each other by keeping the machine parts in a certain interaction.

You have such a gear unit on your bicycle. The distance between the pedal drive and the rear wheel is covered by a chain. On a mountain bike or a racing bike, of course you have not only one gear, but you can choose from many gears. This means that you adjust your speed depending on the force needed and the force to be transmitted and the revolutions per minute. In this case, your toothed wheels are not called cylindrical gears, but chain sprockets.

Install the motor in your vehicle with a chain drive. This is exactly how the transmission is done with a moped or motorcycle. Of course, you can now build your own motorcycle from your fischertechnik parts.

 

Your task:

• Build a copy of the vehicle with chain drive, first only with a crank instead of a motor.
• Turn the crank one time. How many times does the gear turn?
• Turn the crank clockwise. In what direction does the gear rotate?

 

Your task:

• Build a copy of the gear unit.
• Turn the motor on and move the ”gear shift lever” slowly from gear 1 to gear 3. Insure that the toothed wheels for a gear mesh with each other exactly.
• Write down your observations.

This gear unit in gear 3 goes in a different direction than in gear 1 and gear 2. This is because that here, three toothed wheels are in a series.
When an uneven number of toothed wheels are in a series, then the driven gear has the same direction of rotation as the drive gear. This effect is used for a car to drive backwards.

 

Other experiments:

• Build your own model with different numbers of toothed wheels in a series.
• Replace the turntable with a winding drum. Now you have a cable winch like in a crane for various heavy loads.
• Can you put more gears into your gear unit? Experiment with the toothed wheels in your fischertechnik construction kit.
• Expert task: Build a gear unit with a chain.

 

Your task:

• Build a copy of the planetary gear.
• Turn the crank, this is the ”drive”, and observe, which shafts, toothed wheels and toothed wheel combinations you rotate with the crank.

Using the slider, that is the name of the lower part of the lever for your model, you can stop the planet carrier or the hollow wheel so that one of the two parts cannot rotate.

The purpose of a planetary gear is simple. It allows the change of the transmission ratio under load, which means without separation of the flow of force between the drive and the driven gear. Due to the internal toothing of the hollow wheel, the toothed wheels are arranged in a particularly compact manner. For the reverse gear for a planetary gear, no additional shaft with a reverse idler gear is necessary.

In the simplest case, the planetary gear consist of the sun gear, planet wheels, the planet carrier and the hollow wheel. For this simple planet wheel set, a sun gear in the middle is connected form-closed by means of several planet wheels with an internally toothed hollow wheel. The sun gear, planet carrier or the hollow wheel can drive, be driven or stalled. To try out your gear unit properly, you have the slider.
Without an additional toothed wheel, by stalling the planet carrier you can adjust the gear unit so that the output is done one time through the planet carrier and one time through the hollow wheel.

This process is used in vehicle technology to shift into reverse gear. To do this, the drive (the crank) must be connected with the sun gear and the axle drive with the hollow wheel.

 

Your task:

• Test the characteristics of your planetary gear by first holding the planet carrier in place and then drive the gear unit on the hollow wheel.
• Fill in the following table:

 

Bevel Gear Unit

With the bevel gear, you can learn how a simple toothed wheel transmission works.

 

Your task:

• Build a copy of the gear unit model.
• Observe how the revolutions per minute, direction of rotation and the torque change with this model.

This gear unit only changes the direction of rotation by 90°, but the revolutions per minute and torque remain the same.

 

Differential gear

A differential is always needed, for example, for a multitrack vehicle such as a car when several wheels on an axle are driven. Differentials have two purposes: the distribution of the drive power to two axles and the compensation for the difference in revolutions per minute between these branches.

With this function, the differential is used at two locations:

• An axle differential is used on the axle to distribute the power from the cardan shaft to the two drive shafts to the wheels.
• A central differential is used between two axles to distribute the power between the front and rear axle.

 

Aufgabe:

• Baue das Getriebemodell nach.
• Beobachte, wie sich Drehzahl, Drehrichtung und Drehmoment bei diesem Modell ändern. Halte dazu abwechselnd das eine und andere Abtriebsrad fest, dann den Drehkörper (die Aufnahme der Mittelkegelräder) in der Mitte.
• Notiere deine Beobachtungen in der Tabelle:

 

Your task:

• Build a copy of the car jack model.
• Turn the crank one time and observe how far the worm nut moves and how high the lifting arm of the car jack goes.
• Press on the lifting arm. Does the screw spindle rotate backwards?
• Can you name two reasons why a screw spindle mechanism is used for this purpose?

To put the lifting arm in a vertical position, you had to turn the crank several times. You certainly saw that the lifting arm cannot be pushed downwards!

 

 

A screw spindle mechanism has many advantages:

• It reduces the revolutions per minute of the drive many times.
• It is self-locking.
• It increases the force of the drive.

 

Lathe

This model has two spindle drives. The fischertechnik lathe is a model for real pros. Here, two spindle drives interact. Can you imagine why the lathe has two separate spindle drives?

 

Coupler Mechanism-Windshield wiper

Do you really know how a windshield wiper works? The next model shows you how it works. Here, a rotational movement is transformed into a back-and-forth or oscillating movement.

To do this, you need a crank or a cam disk. This gear unit is called a crank-rocker gear unit. It transforms a rotational movement into a straight line movement.

 

Lever

Four thousand years ago, to determine the price of an item, the quantity of the item was compared to weights. This was done using a beam and scales, with which the balance of forces of two weights was measured. For your model, this is a beam attached at the mean pivotal center and the beam has a bowl at each end. Both indicators in the middle of the weighing beam must be in line when the forces are balanced.

These scales work according to the principle of levers of equal length. A lever is a straight beam, which is attached in a manner allowing it to rotate and on which two forces act. The distances between the application points of the forces and the pivotal center are called the lever arms.
Both sides beside the pivotal center are of equal length and equal weight. You know the principle of these scales from a teeter-totter. To have the levers in balance, the weights on the levers and their distance from the pivotal center of the scales must be the same.

 

Your task:

• Build a copy of the beam and scales.
• Put a fischertechnik building block in both weighing bowls. Are your scales working properly?
• Now look for two objects, which have the same weight in your opinion. Put them in the weighing bowls.
• Were you right?

 

Your task:

• Build the scales with a lift arm and power arm and sliding weight.
• Move the sliding weight so that the scales are balanced when no weight is in the bowl. The indicator in the middle of the scales helps you to do this.
• Put a weight in the weighing bowl. Balance the scales with the sliding weight.

 

To put a lever in balance, the sum of the counter-clockwise torques and the sum of the clockwise torques must be equal. This sounds complicated, but it is really not that difficult. The law says that both arms to the left and right of the pivotal center have to have the same weight, but not that they have to be the same length. The farther away a weight is from the pivotal center, the greater the force of the lever and so its weight as well

Lifting tackle with 3 rope pulleys

• Your task:

• Expand your first model to a lifting tackle with three rope pulleys. To do this, look at the construction instructions.
• Pull on the rope again and measure how far you must pull now to raise your load 10 cm. Do you need a lot of force to do this?
• Record and compare your observations.

Now that you know how a lifting tackle works, you can build a lifting tackle with four rope pulleys. In addition, a motor will be installed to replace your force.

Lifting tackle with 4 rope pulleys

Your task:

• Expand the model to a lifting tackle with four rope pulleys and a motor.
• Using regular rubber bands, attach a wallet with coins to the hook.
• Can the motor lift the coins?

The statical characteristics of your model table are the angled table legs. They are stable on two sides due to the angle. The frame construction of the table also includes diagonals and braces. The yellow diagonals between the table legs stabilize the frame with respect to pressure and stress. But, the crowning moment of statics are the connection points, which form triangles. Triangles are also stable when the rods at the connection points have movable joints. Such triangles are called statical triangles. So your model table is statically stable in three aspects.
In statics, all connection points are called nodes.

Your task:

• Build a copy of the table.
• Insure that the diagonals are correctly connected.
• First, put a load on the table from above. Next, press on the table top from the side and then against one of the table legs. What happens in each case?

Your second task:

• Remove the braces and place a load on the table. What effect does this have on the statics of the table?
• Put the braces back in. Remove the diagonals. Place a load on the table again. How stable is your table now?
• Now remove the braces. Place a load on the table. What do you observe? 

A double ladder consists of two halves that are the same, which are connected at a pivotal center at the top. Depending on the angle set for both halves, the ladder can remain standing without any bracing. But at a certain point, the ”feet” of the ladder slip and the ladder halves are pushed away from each other. The bracing stabilizes the ladder.

Your task:

• Build the double ladder, but first without any bracing.
• Set the double ladder up and place a load on it by pressing on the rungs and the upper pivotal center. Does the ladder remain stable?
• Now, install the bracing on your ladder. Now test the ladder again. Does the ladder remain standing now?

Bridge with Underbeam

The bridge with underbeam reminds one of suspension bridges, which spann wild gorges. But this bridge has almost nothing in common with the design of a suspension bridge. You will find out why this is so during experiments with the model.

Your task:

• Expand your first bridge model to a bridge with underbeam.
• Place a load on the bridge in the middle. Now use a weight that is somewhat heavier.

From the load experiments, you certainly found that your bridge is very stable and can withstand large compressive forces. The bridge with underbeam functions due to its trussed construction. This type of construction is suited for large loads, but not for big span lengths. The greatest span lengths are reached with suspension bridges, but they cannot withstand such great forces. The bridge with underbeam and the suspension bridge only look similar. From a statics viewpoint, they are completely different.

Bridge with Upperbeam

An upper boom (upperbeam) bridge can have significantly longer span lengths and withstand significantly greater loads. This bridge also has a trussed design. Strut braces, braces and statical triangles stabilize this bridge.

Your task:

• Build the upperbeam bridge.
• Place a load on the bridge in the middle.
• How has the stability of the bridge changed?
• Name all of the statical elements you know in the diagram: the upper boom, the strut braces, the braces and the supports.

This bridge form can withstand bigger loads than the girder bridge. The compressive force is now transmitted not only to the girder, but is also distributed to the additional components. The upper boom consists of crossed diagonals, which are attached at the upper nodes of the side elements. The diagonals on the upper boom prevent the twisting of the bridge. If the strut braces project upwards, then this bridge design is called a truss frame.

The spatial composition of individual frameworks is called a skeleton. Skeletons made of frameworks are used for houses, high-tension towers, bridge designs and the high hunting stand model. Such skeletons have the advantage that they must not be filled out with a plate, a disk or with stone. In this way they offer less surface to the wind. This type of construction also saves building materials and is still stable. 

Your task:

• Build the high hunting stand according to the model.
• Do you recognize the construction elements?

Your task:

• Build the base for the crane and use the worm gear pair. Can you remember why a worm gear pair is used? Record in the table.
• Next, build the framework. Do you know the statical elements, which are used? Enter this in the table.
• The crane boom is a certain form of a lever. How does the crane still maintain its balance? How is the boom stabilized?

There are several types of gear units available for lifting weights.

• Install the possible gear units in your crane model.
• Compare the way they function.
• Enter the results in the table.

The crowning element for your model is the use of a lifting tackle.

• Develop a lifting tackle for your crane model.
• What do you have to consider, if your crane can also lift and lower very heavy loads?