The Vexmen of Brandywine Robotics

Blog Post

Choosing Your Robot’s Base

Base Styles And Why They Matter

A robot’s base is the platform for your scoring apparatus, it can affect how the robot drives, scores, and moves about the field. A base can help prevent your robot from getting smashed and can help it from tipping over. This year, the Gateway game has lots of tight spots, big game pieces, and tall goals to consider. So choose your robot base wisely.

Here are some factors that can help choose your robot base:

  • Drive type choice – regular, tread, or holonomic
  • Core of stability for the desired height
  • Grabbers influencing base design for the arm/claw grasping game pieces
  • Protecting the robot from damage
  • Ensuring maneuverability and keeping good speed

Basic Robot Base Shapes

Square/Rectangular Base

Square Base Configuration

The square (or rectangular) base is the most logical base when building your first robot. It’s sturdy and does the job. But as you think about the grabber and intake for the game pieces, those walls on the outside can seem a bit challenging causing a bit of rework. However, sometimes a rectangle is what is needed for the game if you are not maxing out to the full 18″ size. That can add to your maneuverability if its small. A rectangle can accommodate a 4 or 6 wheel configuration or even a tank tread. Some people use Holonomic not on the 45 degree offset within the rectangle configuration.
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U Shaped Base

U-Shaped Base Configuration

The U shape is very popular when you consider having an arm to help scoop up game pieces. The U makes for a wide and sturdy wheel base and the U in the middle can help funnel pieces in. Drawbacks to this shape are its size can get in the way sometimes and you can not always get a game piece stuck in a corner. Otherwise this is a fine base to choose. This chassis will fit a four or six wheel configuration. You may also need to have a brace further in the middle to strengthen this base as a true U will be less sturdy on the posts.

Some teams have used the U configuration for a holonomic drive. The front wheels are pointing front/back while the back two wheels are in the side to side configuration. Turning may not be 100% circular as other holonomic configurations but it can get be very lethal.
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H-Shaped Base

H-Shaped Base Configuration

The H-shaped base is another sturdy base using less metal than other bases. The central bar gives structural integrity while allowing for a front and back area for your game pieces. Like the U shape, this can be a bit wide for corners, and the central bar may be too much int he center for your grabber. So think about how you will grab your objects and if the H is right for you.
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Point or Pin Base

Point/Pin Base Configuration

You might say this is not a base at all, but it can be very effective in some games. This has four columns coming down from a tray above holding the wheels. If you want to hover over your game pieces and grab them from the center, this could be very attractive for you. Disadvantages are you have to think about the height as well as the base, the wheels are geared up the column rather than along the floor causing a bit tougher build, and it depends on your game if you need to be hovering over your game pieces.
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Holonomic U Base

Holonomic U Base Configuration

The holonomic base in a U configuration is a take on the U-Shaped base except that the wheels are at 45 degrees making it perfect for a holonomic drive. This is a bit tougher to build than the other bases and adding your sensors on to the wheels is a bit harder as there is less space. Build a prototype out of cardboard before attempting this one. The other drawback is the top of the “U” is smaller than a normal U base since the wheels are coming in at an angle.

However the big advantage of a holonomic drive is getting to exact X and Y coordinates on the game field. The holonomic allows for strafing left to right while keeping your claw parallel to your goal. This can be especially deadly in autonomous programming and with some well placed sensors, your robot will be grabbing the objects with precision and skill. Driving can take some getting used to as you have X/Y on one joystick and rotational movement on the other one.
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Tie Fighter Holonomic

Tie Fighter Holonomic Base Configuration

This is a holonomic base taken from the normal H configuration. Tie Fighter is probably not the real name for this base, but is sounds cool and you get the picture. The wheels on this are at 45 degree angles like the holonomic U base listed above. This base can lead to needing less metal than a holonomic U but it also leaves a lot less room for your game pieces in the middle. This can be even trickier than the holonomic U so please make a cardboard model first instead of hacking up tons of metal.

The advantages listed in the holonomic U are still present with the tie fighter. and if you had two grabbers on each side, you could really have a killer robot.
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Wheels Need Support

VEX CAD Gateway Drivetrain Half2

SuperSonic Sparks Drivetrain

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Your wheels can not be mounted with just one rail. They need to have the axle held up on both ends to work properly. So consider the wheels to be held in a box where the axles can be supported with bearing blocks on both ends. Shaft collars are placed along side a chassis rail and one on the inside to keep the shaft locked in. Gears can be used but wheels can also be driver directly from he motors. Use teflon spacers and bushings to fill out the rest of the shaft.

Plan for Your Sensors Now

Vex Quad Encoders

Shaft Encoders

Sensors help your autonomous and sometimes your free driving as well. Don’t just throw them in as an afterthought as you might find they don’t fit especially well. For a robot base, the shaft encoders are the most important element while other sensors may be placed on or near the robot base. Limit switches, ultrasonic sensors, and line followers are usually somewhere on the base. If you can have the line followers right at the exact pivot point of your robot, it will make adjusting to turns all the easier.

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Other Pictures For Your Enjoyment

VEX CAD Gateway Drivetrain5

SuperSonic Sparks Drivetrain

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Team 1103 U Shape Base