Whole-Group Conceptual Design Worksheet

doledromedaryElectronics - Devices

Nov 29, 2013 (4 years and 7 months ago)


Group Conceptual Design Worksheet


All of the following questions and exercises must be
answered, justified, and

on the public wiki:


Create a representative mission profile for your robot.

Draft a ‘story’ of what your robot does on an average ‘day’ (where day is defined as time
between charges).

Think hard about how long robot actions might take, on average, and
include those estimates in your mission.

Create a list of actions your robot takes, with a corresponding amount of time each of
those actions take. Include details like interacting with
human beings


how long those interactions may take.


Estimate your robot’s maximum size and weight.

You will need values for a representative, well
estimated size and weight to your robot to
reference in your conceptual design. This mea
ns that before you know exactly what
components you have to use, you have to make well
informed guesses

as to which
components you might use and how much they weigh
, use those guesses to drive design
choices, and then eventually compare your final weight t
o your guessed weight to see if
you ne
ed to re
select any components.

You will also need to visualize how large your robot can be when it comes time to
selecting your components. This is critical for the vacuum team, which actually has to
navigate narrow
aisles, but it’s also informational for the vending machine team; ideally,
human beings should be able to step around the machine if they need to in the main

Don’t be afraid to take cardboard out to an aisle and cut it in

Create a table of a
ll of the components you think are going to be included in your robot
design, and how much they weigh. Sum them up for an estimate to use in further design.

Create a 2D top
down representation of how large you think your robot will be (or can
be, in the case of the Vacuum team).


Decide on 2
3 “nice
have” features you want to includ
e in your

As a team, come to a decision on
the top
most design features (in order of design
priority) you want to include in your final robot. These design features must be outside of
the stated requirements for the robot

critical requirements are not
optional, and
must be considered befo

Create a list of your nice
have features, and describe them as fully as you can. Include
rationalization as to why the features deserve the priority you’ve assigned to them.


Conceptual Design Worksheet


All of the following q
uestions and exercises must be answered, justified, and
documented on the public wiki:


Estimate the continuous power
needed to roll the robot around.

Step 1:

Determine the rolling resistance of your robot.

Rolling resistance is

the force
that opposes forward motion that occurs when a round tire or sphere is rolled across a

The gross estimation of this force is

= CN
, where
is the linear force,
is the
rolling resistance coefficient (assume a coefficient of
, slightly higher than car tires on
concrete), and
is the normal force of the robot on the ground; i.e., how much it weighs
(assuming a flat surface).

Step 2: Decide on the average speed of your robot.

Set up an experiment where one of
your teammates is walking at the average speed you decide for your robot. Blindfo
ld that
Have a fellow teammate cross their path, and have a third teammate yell ‘
when the third teammate determines the second teammate is an obstacle. Use this
experiment to guide how quickly you really want your multi
pound robots to

Step 3: Estimate any additional forces the robot might experience that impede

If your robot is, say, pushing a broom, estimate (and defend!) how much
force that might take to do so continuously.

Step 4: Generate an estimate of power.

Multiply the sum of your forces by the
expected velocity
(stay in metric, so that you get

a wattage)
of the robot
to generate a
continuous power requirement.

Don’t forget to document all of the previous steps on the wiki, and tell your electronics
team your findings.


Look for appropriate motor and wheel combinations

Step 1: Estimate how large

of a drive wheel you think you need.

Given the weight of
the robot and the potential available internal space, figure out how large of a wheel you
think you might need. Check wheel load ratings on websites like
, and more to figure out what kind of
wheel would be most appropriate.

Step 2: Determine your shaft angular velocity from your wheel size and average
your estimated wheel diameter and linear velocity to create an estimated
average speed for your robot. No formulas given here

you’ll have to find them on your

Step 3: Create a trade study of motors that might be suitable to drive your wheels,

your power and speed requirements.
Visit websites like


to start your search for motors that
might be appropriate.

t at least 5 choices of motors and gearheads that may be
appropriate for the task

write down their free speed, stall torque, nominal voltage, price,
weight, and anything else that might seem pertinent. If the motor/gearmotor speed is
within 4x the speed
you desire, assume we can gear it down with chain drives or gears.

For now, assume that the transmission of power from your motor to your wheels will be
90% efficient, and that the power required to drive your robot should be 10
20% of the
motor’s maximum
available power (and thus, that the speed of your robot should be
within 80
90% of the motor’s free speed).

Step 4: Create a decision matrix and pick a motor.

Decide what values are important
to you

examples of things you might care about are how close
the motor’s free speed is
to what you need, how much the motor costs, how much the motor weighs, what kind of
voltage the motor needs (here’s a hint

your electrical team is likely going to be upset if
you choose anything that needs substantially higher t
han 12 volts), how easy it is to make
use of its output shaft, etc.

Again, document all these steps on the wiki.


Start deciding on any other mechanical components you might need to make your
robot work.

Do you need a vacuum? A broom? Bumpers? What other
mechanical components do you
need to include on your robot? Decide on major components you’re going to need to
include in your robot design, and start thinking about what motors or other devices might
be needed to power them.


Conceptual Design



All of the following questions and exercises must be answered, justified, and
documented on the public wiki:


Estimate power draw that corresponds to your mission profile.

Figure out what parts of your robot are going to demand what amounts of power during
your mission profile. Your mechanical group is c
reating an estimate of the continuous
power needed simply to roll around

get this value from them when they’re ready, and
apply the continuous power rating to the ‘moving’ parts of the mission.
Estimate the
power needed from any devices you know are goin
g to be installed on the robot

vacuums, inverters to power the vending machine, lights, boomboxes, etc. Add these
powers to all the appropriate columns.

Add a column to your mission profile called ‘Estimated Power’
, and fill in the blanks
Create an estimated average power for your mission using the
time spent in each stage
and the power draw associated with that.


Select the batteries required.

Step 1: Determine the system voltage of your robot.

Work with your mechanical team
to determine
the nominal system voltage of you robot. You’ll want a voltage that can
drive your motors, while also being able to power any accessories you might need. Most
likely, you’ll be running on a 12 volt or 24 volt system, but I leave that up to you to
finally d

Step 2: Determine the average current draw of your robot.

Divide the average power
for your mission by the system voltage to get average current draw. Multiply your
average current draw by your mission time in hours to get a representative “Amp

rating for your robot.

Step 3: Look for batteries.
Check out websites like

and start
looking for batteries that would be appropriate for your robot.
Assume that the final
battery system s
hould provide at least 2x more “Amp
Hours” than your robot will need,
for the sake of having sufficient overhead to complete its mission. If you need more
Hours, you can designate batteries to be in parallel; if you need more voltage, you
can designate

batteries to be in series.
Only sealed lead
acid batteries and
advanced glass mat batteries will be allowed. Create a list of 5 or so possible battery
combinations (i.e.

one big battery, multiple small batteries in parallel, two batteries in
s, etc.), and document price, weight, physical size, etc.

Step 4: Decide on a battery combination.

Create a decision matrix, choose values that
are important to you, and come up with a recommendation by the end of class.


Select motor controllers

Once the mechanical team
selects motors, start looking at websites like


for motor controllers. Look for
motor controller
s that can at least handle ¾ of the selected motor’s stall current.
Try to
find at least 3
5 options of motor controllers that could drive the selected motors, and
create a decision matrix to justify which motor controller you recommend.


Start working on
a diagram of your electrical system

What other bits and pieces do you need for a complete electrical system? Do you need an
on/off switch? (Yes.) Do you need several e
mergency stop switches? (Yes.) Brainstorm
additional electrical pieces that you may need
to include in your electrical system.

Control System

Conceptual Design Worksheet


All of the following questions and exercises must be answered, justified, and
documented on the public wiki:


Figure out what the hell kind of sensor design you need on your robot to successfully
and safely follow a line.

Take your 2D robot mockup out to the lanes and determine what ki
nd of sensor design
you need to safely detect the line and any and all intersections of the line. Decide where
the sensor needs to be placed on the robot, what (if any) mechanical actuation the sensor
needs to figure out if it’s hit an intersection, and wh
at your robot would need to
physically do (if anything) to follow the line.


Research into potential line, line sensor, and absolute location detection designs.

What kind of line couldn’t possibly be obscured? What is the most impervious to dust?
What is

the most impervious to floor
mounted obstacles? Think hard about what kind of
sensors could possibly be used to detect lines on the floor, and think about what kind of
sensors would be best to determine absolute location in the space. Don’t limit yourself

just steel tape or just RFID

do some research, and look into it. Come up with a decision
matrix to justify what kind of system you recommend, and justify it to the other team

you will ultimately have to have the same system, so you’ll have to convi
nce each other.


Start thinking about what human safety and obstacle avoidance sensors are going to
be required.

How are you going to detect human beings with enough time to stop the robot? Where
does the sensor sense in the first place? How many different
types of sensors do you need
for robust detection of all the different kinds of obstacles you remember encountering in
your walk
throughs? Think hard about what sensors would be most appropriate, and how
robust those sensors may be to the operational envir
onment. Start putting together