First Full Week of Robot Building! Drivetrain is coming together

Step one to any robot build is the base. The drivetrain consists of the wheels and motors and frame that serves as the base of the rest of the robot. We work from bottom up when we build, so during the past week we've been working almost solely on the drivetrain of our robot.

The biggest challenge this year? The barrier around the warehouse. According to the game manual, this barrier is defined as "approximate 1-inch high by 5.5-inch wide (25.4 mm x 139.7 mm) obstacle on the Playing Field". The barriers surround part of the border of the warehouse and the shared wobble goal. The most efficient way to reach these locations on the field is to design a robot that can go over the barriers.

A map of the field denoting the barriers around the warehouses and shared shipping hub

Several things came up with the design of last year's drivetrain that wouldn't work this year. First, the position of the wheels. Our previous drivetrain had the wheels positioned so that the frame itself was only about a centimeter off the floor. We don't want our robot to get stuck on the barriers and bottom out; that would be game over for us. Luckily, one of our teammates had the idea to mount the wheels underneath the channel we are using for the frame. That way the frame is elevated higher off of the ground and won't bottom out on the barrier.

Second problem: the type of wheels. We have both mecanum wheels and omni-wheels, but we also have normal wheels with rubber tires (we call them grip or traction wheels). Though mecanum wheel give us the best maneuverability in tight spaces, we don't think we'll need to move side-to-side like we did last year to position ourselves to launch the rings. This year, we will likely only need to turn in place in tight spaces like the warehouse, and a tank-drive train could do that just as well as a mecanum drivetrain. Now we were stumped. There was only one other thing to compare the two types of wheels: radius. This kind of goes back to the whole lifting the frame up high enough that it won't bottom out, but the larger the radius of the wheel, the higher up we would be. Our mecanum wheels have a radius of 1.5" and our grip and traction wheels have a larger radius of just over 1.75". A quarter inch isn't a whole lot of difference, so there was much debating over the pros and cons of each type of wheel. In the end, we decided to use the grip and traction wheels and create a tank-drive robot.

Third problem: motors. As most of you should know, there is a motor limit in FTC. Based on some of our drawings and brief designs for the rest of the robot, we would only reach the motor maximum if we used four on the drivetrain. The question is, do we want to risk it and use four on the drivetrain and end up needing another motor for something else on the robot. More motors on the drive train give it more power and make it move faster. We decide it's worth the risk. Besides, we can easily switch to mecanum wheels if we decide we need to since we have four motors.

All problems solved, we made a CAD of our design. It's a bit complicated to explain, so I've put some images for you to get the general gist of it.

Building also started this week. We are currently about 2/3 of the way done with our drivetrain, and waiting on a few parts to come in the mail. Next week we hope to move on to building a claw that will pick up the freight pieces and our team scoring element. We've already been working on the design for these things, but I'm going to leave you hanging until next week's blog! :)

Brainstorming and researching ideas for the robot

Making a CAD of the other parts of our robot

Most of our team works on building the drivetrain

Thank you for supporting our team by reading our blog posts. Though you may not think you're providing us with anything useful, seeing the large numbers of views on each blog post is a huge moral booster for our team. You can support our team further by following us on Instagram @batteriesnotincludedftc and checking out our Sponsors and Donations page on our website. Thank you to everyone at FIRST, all the volunteers, and our parents and coaches for making this season possible, and good luck to all the FTC teams competing this year!