Plan your mechanism
Turn a robot task into requirements you can measure, compare, and test.
Before drawing a , write down what it needs to do, the limits you have to work within, and how you will test it. One page is enough for a small mechanism.
Suppose your team needs a roller to move a game piece from the into a claw. “Make a fast transfer” leaves a lot unanswered. Where does the game piece start? Which way should it face when the claw grabs it? What happens if it comes out of the intake crooked? How much room do you have?
Write those answers down so everyone is designing for the same job. They also give you a way to compare ideas before spending time on detailed .
Plan the handoff
Start with the actual game piece, intake, and claw. Measure several game pieces if you can. Check their size, where they flex, and whether seams or other features affect how they roll or grip. Try feeding them through the intake in different ways and see how they come out.
Draw a side view and a top view. Show the game piece in the intake, as it moves toward the claw, and inside the closed claw. At each step, show where it sits and which way it faces. Reaching the claw is only part of the job: the game piece also needs to be at an angle the claw can grab. In robotics, means position and orientation together.
Use these questions to describe the handoff:
- How does the game piece come out of the intake? Could it be sideways or off to one side?
- Where does it need to be for the claw to grab it? Does it need to face a certain way?
- What holds it up while it moves from the intake to the claw?
- If the handoff fails, what can the driver do to try again?
Add sketches, , and photographs where they help. For example, draw arrows on a photo of the intake to show where the game piece can sit.
Requirements, constraints, and preferences
A requirement says what the design has to do. A limits your choices, such as a fixed mounting face, , or manufacturing process. A preference helps you choose between designs that meet the requirements and constraints.
For example, suppose your intake and claw are already built, and their mounts cannot move. Your team can make custom parts with a 3D printer and drill press. You decide that the transfer must complete each handoff within two seconds.
Your plan might look like this:
| Type | Example | How to check |
|---|---|---|
| Requirement | Deliver the game piece into the claw without dropping it | Try handoffs from different positions in the intake |
| Requirement | Complete the handoff within two seconds | Time from starting the transfer until the claw holds the piece, including retries |
| Constraint | Keep the existing intake and claw mounts | Check the transfer's full movement in the current |
| Constraint | Make custom parts with the printer and drill press | Ask the builders to check how each part will be made |
| Preference | Give the less weight to move | Compare the moving mass of designs that meet the requirements and constraints |
The two-second limit is a requirement because you chose it as a pass-or-fail target. The tools and existing mounts are constraints because they limit how you can build the transfer. Lower weight is a preference: if two designs both do the job within those limits, you would favor the lighter one. A light design that keeps dropping the game piece still needs fixing.
Choose timing and success targets that suit your robot; two seconds is just this example's target. For a reliability test, record how you place the game piece and what counts as a successful handoff, so everyone tests the same thing.
Check the current game manual for rules that affect the design, including size, extension, materials, motors or , and game-piece handling. Keep the relevant rule references with your notes so the team can find them again.
Compare different mechanisms
two or three ideas before choosing one to model in detail. You could try a claw that swings the game piece over, rollers that push it along a guide, or a claw that moves toward the intake to pick it up.
Think through the whole handoff for each idea. Rollers need guides, supports, a connection to the motor, and somewhere to hold the game piece until the claw is ready. Claws need room to open, and the code has to open and close them in the right order. Include what the programmers must write and what the driver must do.
You can use a small decision table:
| Question | What to record |
|---|---|
| Can it pick up and deliver the game piece? | A sketch with dimensions showing both positions and which way the game piece faces |
| What is uncertain? | The contact, , or movement you have not tested |
| Can the team build it? | Stock, tools, purchased components, and difficult operations |
| Can it be repaired? | Removal steps and parts needed for a replacement |
| What would make it fail? | A specific problem, such as dropping the game piece while turning |
If an idea cannot get the game piece into the claw, change it or set it aside. A low cost or weight does not make up for being unable to do the job.
Prototype the uncertain part
A answers a question before you commit to the full design. It can be cardboard, a printed guide, or two rollers on adjustable mounts.
If the uncertainty is ball contact, test the roller spacing and guide shape. You do not need a finished for that experiment. If the uncertainty is access to a mounting screw, a full-size cardboard mock-up may be enough.
Write the question before making the prototype. Then record what changed between attempts, the starting conditions, and what happened. Keep failed attempts: they often explain why the final geometry has a guide, a larger opening, or a different pivot.
Before you start CAD
Before you start detailed CAD, put your notes, measurements, purchased-part models, layout sketch, and prototype results in one place. Include the mounting-hole positions and the surfaces the new part will attach to. Make clear which dimensions are fixed and which can change.
For example, you cannot move the holes in a rail you already own, but you may be able to change the gap between two custom side plates. Agree on that before teammates start designing parts around them.
Use Measuring parts to collect dimensions, then Layout sketches to turn your plan into a layout the team can use. If CAD is new to you, start the Onshape lessons alongside this work.