Motor actuators

Although pneumatic actuators are commonly applied to many devices and machines that require remote or automatic movement, motor actuators are also used for many applications.  In this segment students will have an opportunity to build working models of motor actuators, apply these actuators as practical muscle replacements for arms and legs, and then test the parameters of work an motor actuator arm might be able to do based on leverage, motor lift force and distance.

There are three basic stages in this segment: 1) Build an actuator,  2) Test the actuator, and 3) Apply the actuator.  For an overview of what will ultimately be accomplished by following these processes, watch the following clip:

WHAT YOU WILL NEED FOR THIS EXPLORATION

• Clean foam trays (such as those used to package meats). Trays can be purchased in bulk or can often be donated by the local grocery store if you indicate what you will be using them for a school project.

• A knife or box cutter for the foam

• A hot glue gun

• Straws

• Brass clasps used in holding papers together

• Large Washers

• Force scale

• 3-4 inch 6-32 or 8-24 screw and matching nut

• Plastic insulation from wire and aquarium tubing to size

• AA, C or D cells and connecting wire

• Switch (See Polarity Circuit)

• Hobby Motor. (See About DC  Motors)  

1) Making a Actuator

Start with a foam tray you might find when you buy a piece of meat in the grocery store.  Clean and dry the tray.  The best trays are sturdy, tough foam.  Color is usually not an indicator of strength, so you will need to test various kinds of trays to see which are most suitable.  

A) Using box cutter or other thin, sharp blade, cut a piece that is about 13 x 5 cm.  Size is not of critical importance as we shall see in a few frames.  Have plenty of foam board available so that students can make mistakes and try again.

B) On one end of the foam board, hot glue three pieces of foam so that it forms a corner box. The size is not critical except the depth of the box should be at least 4 cm tall.

C) At the end of the box you have created, punch two holes, one above the other, with the pointed end of a pencil.  One large enough for a long screw to pass through without binding and another for a straw to pass through, also without binding.  Look ahead to see how this works before boring your holes.

D) Set aside the foam strip and box.  Cut a small piece of foam approximately 2 x 4 com in size.  Bore a hole in the foam on one end as shown below and insert a nut that corresponds to the long screw.  If you press the nut into the foam correctly it will stay in place without glue. Adding a bit of hot glue to the edges of the nut ensures it will not work loose.

E) On the same small piece of foam where you placed the nut, cut another hole at the other end and hot glue a straw in place as shown.

F) Prepare your DC electric hobby motor by finding a plastic sleeve that will fit snugly over the the shaft of the motor and then that will adapt to a small piece of plastic tubing.  In the example below note how the shaft was fitted with a piece of plastic insulation from a common electric conduit found in household wiring. The rubber tubing was a small aquarium pipe.  The connections need to be tight enough so that when the motor turns, the screw will be driven without slipping.

G) For the final assembly, insert the straw into the to hole of the box assembly and then insert the screw into the lower hole and run it through the nut several turns.  Attach the motor and plastic coupling sleeves as shown.  Test the apparatus to make sure that when the motor shaft moves, it turns the screw and moves the foam piece and straw easily.  When you are confident that the motor action will move the straw back and forth easily, then hot glue the motor to the foam base.

H) For the last step, test your actuator and make adjustments as necessary.  It should work easily as this example in the video below:

CONTINUE TO TESTING THE ACTUATOR

 Have students make notes and drawings in the Engineering Notebook of the entire process as well as their observations and reflections about their work with building something of this complexity. Were they feeling successful? frustrated? curious? etc.