Introduction to Robotics
Teachers Notes
Activity 10: Compound Gears and Arms
Activity 10: Compound Gears and Arms
Activity Setup
Calculations
Reliability
Interest
Activity Time
120 Minutes (10 minutes
once the arms and gear box
sides have been cut and
folded.)
Simple
Good
Excellent
150 minutes
Objective
At the end of this students will:
1. Differentiate between simple gear and COMPOUND GEAR systems.
2. Identify the DRIVING GEARS and the DRIVEN GEARS in a COMPOUND
GEAR system.
3. Determine the GEAR RATIO for COMPOUND GEAR systems.
4. Test a simple gear and a compound gear system on a robotic arm.
Materials:
BaseBot with Vex Controller
Computer Workstation with Easy C™ installed.
Orange Serial interface cable.
Arm Kit
Metric mass set
Soup can
Vise or 2-ton press to bend metal
Hacksaw or band saw to cut metal
Drill press to drill holes
Sheet steel or sheet aluminum to make arms
Hazards:
Always make sure the controller is turned off when plugging in or removing
cables!
Never plug the orange interface cable into the Rx1 or Rx2 Port!
Make sure that the battery is plugged in properly.
Make sure the Transmitter Frequency and the Receiver Frequency Match.
Make sure that the other BaseBots are using a different frequency.
Make sure the robot is OFF when working on the arm and/or claw.
Keep fingers away from arm gears and claw gears.
Make sure HAIR is TIED BACK!!!
Teaching Strategies:
General:
Safety is very important. When working with robots that have arms make
sure hair is tied back and the students do not work on the arm or the gear
box when the robot is on.
It is very important that the power switch on the controller is in the OFF position
when plugging cables into the controller. If the controller is ON, a static charge
may burn out the controller while the cable is being plugged in.
Make sure the robot is propped up off the table so that the wheels are not
touching. Many times there is an old program in the controller and when it is turn
on it starts moving. It could roll right off the table top. The top cover of a 50 pack
CD spindle works well for propping up the robot as do the four larger extra
wheels in the kit.
Making the Arm Tower Side
Take a Vex 5 x 15 hole plate and cut it so that it becomes a 5 x 10 hole plate.
Place the last row of holes in a vise and tighten. Bend the plate so that it is at a
90° angle to the holes in the vise. Repeat for second side. If you have access to a
two ton press in a metal shop, a much better bend will be obtained.
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Making the Arm Pieces:
Measure a piece of sheet steel or aluminum so that it measures 3”x 9”. Using the
measurements on the template below mark and drill the mounting holes. Make
sure that a drill press is used to drill the holes. Finally, fold the metal using a vise
or a press. Again a press will yield better results. It is important to get the holes on
the sides directly across from each other or the gears will not sit properly.
Soup Can Bucket
Punch two holes into an empty soup can. Add a coat hanger wire to make the can
into a bucket. Add a bolt hook to the end of the arm to hold the bucket.
Activity:
In this activity the students will learn about compound gears, compound gear
ratio, how to build an arm, and how to program a non-drive motor. It takes
patience to put the arms together especially if a student has big fingers or is
working by themselves. This activity can take anywhere from 1-3 hours
depending on how comfortable the students are with the building process.
In some cases the robot may tip forward and over before the arm fails to lift the
mass. This could lead into a good discussion about the center of mass. If this
happens, the students could clamp the robot down to prevent the robot from
tipping.
If you have extra time, it may be interesting to have the students create the fastest
robot they can using compound gears and then have a race.
You may also want to have the students test various compound gear combinations
with the gear tester as they did in the previous activity.
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Assessment:
Student Worksheet Answers:
1.
System Type: Simple
DRIVING
DRIVEN
Gear Ratio: 12:60 or 1:5
System Type: Compound
Gear Ratio: 84:12 and 84:12
7:1 and 7:1 so
49:1
System Type: Compound
Gear Ratio: 12:36 and 12:36
1:3 and 1:3 so
1:9
System Type: Simple
DRIVEN
DRIVING
Gear Ratio: 60:36
1.66 :1
2. Complete the data table for Arm Testing.
Gear Ratio: 5:1
Mass Lifted: Results will vary should be
less than one below.
Gear Ratio 1st Pair: 5:1
Gear Ratio 2nd Pair: 5:1
Overall Gear Ratio: 25:1
Mass Lifted: Will vary
3. The second combination should lift more weight it has a 25:1 ratio which
means five time more torque/ power than the 5:1 ratio.
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