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Electronics Investigation and BumpBot Construction Part 1 Diane Brancazio, MIT Edgerton Center dianeb@mit.edu 6/5/2018 Summary: Students will investigate electronic components and switches and learn how they can be used to perform logical operations. They will create a prototype board for the obstacle-avoiding “BumpBot” rover.

Part 1 Electronic Component Investigation and BumpBot wiring (1 ½ to 2 ½ hours) Materials: For each BumpBot builder

• 2 motors with ½” long rubber spline on shaft

• 2 Wires for each motor, stranded, 24 AWG, 8” long

• 2 SPDT Limit switches (NO/NC) • 1 toggle/slide switch • Alligator clips • Binder clips • 2 battery holders, each 1 AA • 2 AA batteries • Cardboard sheet ~ 8” x 10” • Circuit Basic Handout

Tools:

• Wire stripper • Needle-nose pliers

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Procedure:

1. Introduce the components and recall knowledge/questions about electronics.

a. Distribute materials and tools b. Invite students to Tinker. Try these investigations:

i. Make circuits using any of the components and observe the behavior

ii. Use circuit to demonstrate/explain electrical terms students already know

1. Series circuit, Parallel circuit 2. Open Circuit, closed circuit, short circuit 3. Limit Switch, Slide Switch 4. “Single Pole – Single Throw” switch, “Single Pole

– Double Throw” switch iii. Refer to Circuits Basics Handout or other resource, and

sketch circuits on board as desired c. Discuss

i. Where are circuits like this found? ii. How are switches “logic” components? iii. How can these circuits be used in a toy robot where

decision-making is performed without a computer?

2. Prepare the motors. Mark the motors L and R as shown in the image. Strip the 8” wires about 3/8” (1 cm) each side and solder to the motors. The color of the wire doesn’t matter to the circuit, but choosing wire colors as shown in the image will make the circuit easier to understand.

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3. Mount the motors on a cardboard sheet as shown using tape or a small amount of hot glue, taking care not to let glue get into the openings on the back of the motor. Only the right motor is used for the next steps, so you may want to tape the left motor out of the way.

4. Add the first battery holder with red wire towards the top of the cardboard sheet. This will be the FORWARD battery. Use binder clips or paper clips to connect the wires to the circuit and make the motor spin. Switch the wires and observe the motor’s behavior.

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5. Control the motor with the SPDT Limit switch (Single Pole Double Throw). This switch connects the Common tab to either the NC (Normally Closed) tab, or the NO (Normally Open) tab.

a. Look at the switch closely and look for tabs marked COM, NO, NC. COM will be near the lever pivot.

b. Mount the switch as shown with a small amount of hot glue, taking care not to impede the action of the lever. The 45° angle of the lever is important!

c. Connect the top motor wire to the COM tab of the SPDT limit switch. Twist the wire, thread it through or around the tab, and squeeze with the pliers.

d. Use an alligator clip connector to investigate the performance of the NC and NO connections.

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6. Use a second battery to create forward/reverse motor action.

Add the second battery, this time with the black wire on top. a. Connect the bottom wires from both

batteries (one red, one black) using a binder clip or paper clip).

b. Make connections from the 2 batteries to the SPDT limit switch as shown, or as described here: Twist the wires, thread them through or around the tabs, and squeeze the wires with the pliers. Soldering comes later.

i. Connect the red battery wire from the first battery to the NC connection.

ii. Connect the black battery wire from the second battery to the NO connection.

c. Verify that the motor spins in opposite directions depending on whether the switch is depressed or not.

d. Discuss how the batteries are used in this circuits. This is not a traditional forward reverse implementation. The battery on the right is the battery creating FORWARD motion, while the battery on the left creates REVERSE motion. Notice that the bottom ends of the batteries are connected. What problems/features could come up from this configuration?

FORW

ARD

REVE

RSE

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7. Add the Left SPDT limit switch and control the Left motor. This a. This switch is symmetrical to the

right limit switch. COM, NO, NC will be mirrored. Mount the switch as shown with a small amount of glue, taking care not to impede the action of the lever. The 45° angle of the lever is important!

b. Connect the top motor wire to the COM tab of the SPDT limit switch. Twist the wire, thread it through or around the tab, and squeeze with the pliers. Soldering comes later.

c. Bring power from both batteries over from the right limit switch to the left limit switch. An easy way is to “daisy-chain” it from the first. Make connections to the NC and NO tabs with Alligator clips from the corresponding tabs on the right limit switch.

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8. Replace the alligator clips with small wires a. Cut pieces of red and black wire about

3” long. Strip the ends 3/8 inch (1 cm). b. Twist the wires, thread them through

or around the tabs, and squeeze with the pliers.

i. Use red wire to connect the NC tab from the right switch to the left switch.

ii. Use black wire to connect the NO tab from the right switch to the left switch.

c. Verify that both motors spin in opposite directions depending on whether the corresponding switch is depressed or not.

d. Discuss how the batteries are used in this circuits could be used to control a toy robot. What problems/features could come up from this configuration?

9. Add an On/Off switch

Use the toggle slide switch to replace the binder clip connection, and make it switchable. Choose either tab on the toggle/slide switch - they will be closed (connected) and opened (disconnected).

a. Mount the switch with a small amount of hot glue, taking care not to impede the action of the slider.

b. The wires will be twisted, threaded through or around the tabs, and squeezed with the pliers, to be soldered later. If the wires strands of wire do not all fit, cut off up to half of them and try again.

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i. Connect both bottom wires from the motors and bring to one tab of the slide switch.

ii. Connect both bottom wires from the batteries and bring to the other tab of the slide switch.

c. Verify the circuit and solder the

twisted connections.

d. Learn the tools and practice soldering wires if you have not done so before.

10. Add “feelers” to the limit switches. Use large paper clips or wire to create extensions the levers on the limit switches. Fasten them with thin plastic tubing.

a. Use plastic tubing that fits snugly over the switch lever. Heat-shrink tubing may work. Cut small pieces about ½ inch.

b. Squeeze the tubing and slide it on the lever. Make sure it does not interfere with the moving piece near the pivot.

c. Create “feelers” from paper clips by straightening them with needle-nose pliers then bending the back the end as shown. Make sure the end is flat and close.

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d. Insert the feelers into the tubing as shown.

e. Bend the feelers so they can move freely.

Verify the construction and operation of this prototype board

f. Check that all connections are soldered well g. Turn the power switch to On and check that both motors

spin “forward”. h. Depress each feeler/lever to verify

that motor direction reverses. i. Note that when the power switch is

in the Off position the motors will still turn on when the switches are depressed. This is due to the “common ground between the batteries”. To eliminate all motor action, remove one of the batteries.