Whole-Group Conceptual Design Worksheet

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

  1. 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 and obstacles, and how long those interactions may take.

  1. 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 means 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 to your guessed weight to see if you need 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 aisles. Don’t be afraid to take cardboard out to an aisle and cut it in-situ.

Create a table of all 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 possibly be, in the case of the Vacuum team).

  1. Decide on 2-3 “nice-to-have” features you want to include in your design

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 – mission-critical requirements are not optional, and must be considered beforehand.

Create a list of your nice-to-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.

Mechanical Conceptual Design Worksheet

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

  1. Estimate the continuous power needed to roll the robot around.

Step 1:Determine the rolling resistance of your robot. Rolling resistance isthe force that opposes forward motion that occurs when a round tire or sphere is rolled across a surface. The gross estimation of this force is F = CN, where F is the linear force, C is the rolling resistance coefficient (assume a coefficient of .02, slightly higher than car tires on concrete), and N 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. Blindfold that person. Have a fellow teammate cross their path, and have a third teammate yell ‘stop’ when the third teammate determines the second teammate is an obstacle. Use this experiment to guide how quickly you really want your multi-hundred-pound robots to move…

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

  1. 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 speed. Use 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 own!

Step 3: Create a trade study of motors that might be suitable to drive your wheels, given your power and speed requirements. Visit websites like and to start your search for motors that might be appropriate. Document 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 than 12 volts), how easy it is to make use of its output shaft, etc.

Again, document all these steps on the wiki.

  1. 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.

Electrical Conceptual Design Worksheet

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

  1. 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 creating 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 going 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.

  1. 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 decide.

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-Hour” 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 should 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 Amp-Hours, you can designate batteries to be in parallel; if you need more voltage, you can designate batteries to be in series. NOTE: 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 series, 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.

  1. Select motor controllers

Once the mechanical team selects motors, start looking at websites like and for motor controllers. Look for motor controllers 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.

  1. 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 emergency stop switches? (Yes.) Brainstorm additional electrical pieces that you may need to include in your electrical system.

Control System Conceptual Design Worksheet

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

  1. 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 kind 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 what your robot would need to physically do (if anything) to follow the line.

  1. 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 to 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 convince each other.

  1. 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 environment. Start putting together recommendations.