Building first robot (line following)

Community General Discussions
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I’m building my first robot and I’m looking for some help with my design, specifically selecting power and motors since those seem like items I don’t want to screw up. My microcontroller will be a Raspberry Pi (5V 1A). My robot is going to be a 25lb (worst case) line following robot that will carry a laptop USB connected to the Raspberry Pi. It will follow a turning track that I expect to be about a 200m loop. Speed is not a priority as the robot will be making a dozen or so stops along the track for 2-5 minutes at a time to take some readings and measurements. So if I traverse the track in an hour or two I will be fine as long as I can do it on a single charge. I’m anticipating tires of probably 4" or maybe 6" lawnmower wheels but I’m not very sure about that yet. The floor is linoleum tile. My peripherals will be a light/color sensor, two distance sensors and potentially a stepper motor in the future.

Based on some research it looks like I will want to use two 12V geared DC motors with a motor controller board and a 12V to 5V power distribution control board. Using the drive motor sizing tool on this website I came up with a required torque of ~16 ozf in (my inputs: 25lb, 2 motors, 12V, 2m/s, 0.2m/s2, 2 hour run-time, 2.5" wheel radius). Does that sound reasonable and does anyone have any suggestions for reliable motors and motor controller they would recommend? What would be the best way to power this? A bank of D batteries or maybe a 12V lead acid battery? Is 12V my best option?

Other questions I have:
Would a design of 2 rear motor driven wheels and 2 front casters work for my robot or will 2 front casters cause me problems?
Do I need an encoder in my motors?
Do I need a PWM pin on my microcontroller for each DC motor I want to control?

I appreciate any help,
Larry

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Will the robot be going up any inclines?

Lead acid are some of the heaviest batteries you can get and although they can easily provide the necessary current, their weight usually offsets any advantages they provide. NiMh is what is most commonly used and the higher the capacity (rated in “amp hours”, the longer the robot will run, but also the heavier the pack will be.

Really up to you, but most designs have the casters in the rear

If you want the rover to go perfectly straight, then encoders will be needed, since even two supposedly identical motors from the same manufacturer have subtle differences.

You really only need one dual motor controller.

Why do you have both a Raspberry Pi and a laptop? Also, is there any reason why you want the robot to be so heavy?

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Thanks for the information Coleman. I will not have to deal with any inclines. I need the laptop because manual tests are being done using software on a laptop. The robot needs to mimic those tests at various locations along my path so the raspberry Pi will kick off those apps on the laptop at specific locations. The weight assumes supporting up to a 5lb laptop, a 3’ high support structure for the laptop to sit on for testing and ease of use and potentially adding a turntable on the top of the robot to rotate the laptop. 25lbs may be a little high but it will probably end up being close.

-Larry

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Seems similar to this, but with even more features:
robotshop.com/en/superdroid- … robot.html
Perhaps the specs can give you some ideas.