Multi-shot Cannon Specs

Build a mechatronic device capable of shooting projectiles and striking static and dynamic targets.

General Project Requirements:

The device must be portable with a maximum volume of 2’x2’x2’. However, the volume constraint may be relaxed at the discretion of the instructors, so contact them if you think your design requires different dimensions.

You may use wall power but must use a dedicated supply (such as a PC power supply) for the final product. Battery-operated devices are another possibility for greater mobility. You may not rely upon the laboratory bench power supplies to run your device.

It is important to keep your project cost at a reasonable level. To that end, please keep an ongoing budget of parts used/purchased for your project. The reimbursement guideline is $350, subject to negotiation with the instructors. This refers only to actual expenditures, not parts purchased by the instructors for the class. The following items are not included in the reimbursable amount:
- ~$60 worth of motors (e.g. 2 DC motors, or 1 DC and 2 servos)
- ~$50 toward the microcontroller of your choice (unless you use NI products, which are provided free of charge to you)
- Some low-cost sensors (Omron decoders, potentiometers, switches, etc.)
No sales taxes will be reimbursed. All reimbursed items and parts supplied by the instructors are kept by the instructors. Teams are encouraged to scavenge for items, but even if you don’t pay for something, please list it in your budget with an estimated cost when applicable.

Construction and Aesthetics
The device must be robustly constructed: use nuts and bolts, machine screws, cable ties, proper soldering, etc., rather than provisional methods. No prototype kits or toys may be used. Appearance counts. “Rats’ nest” wiring, duct tape, bubble gum, or otherwise rickety-looking devices are discouraged not only for lack of aesthetics, but also because they tend to be less robust.

The machine may not damage anything with which it interacts. Please prioritize safety when building and testing your device.

A schematic of the target setup is shown in Figure 1. The targets will be located 10’ away from the cannon, in a 4’ wide x 3’ high area. There are three total targets, each 8” in diameter and covered with a different color of retroreflective tape (red, green, or blue). The targets are located at a fixed height, with the bottom target being 1’ higher than the base on which the shooter will be placed. During performance tests (described in detail in a later section), each of the targets may either be stationary or moving with a maximum speed of 1 ft/sec. The targets will always be in the “field of play,” meaning they are always visible and able to be hit. Since the targets will need to stop and change directions periodically on the 4’ long track, the speed will not be constant. However, the motion will be predictable and simple tests should allow for easy adjustment of machine timing.

The projectiles that the machine must fire are Nerf ballistic balls (~1.5” diameter), shown in Figure 2. These will be provided by the instructors and six balls will be used per test. The balls must be dumped from a container into some part of the machine (e.g., a hopper/feeder subsystem). Teams are prohibited from manually placing balls individually into any part of the machine.

Performance Evaluation
During the final lab demonstration, each machine will be required to complete a series of performance tests. A separate public demonstration will be held on a different day. Prior to each test/round of competition, a team will carry their device to the shooting platform and have ample time to position the machine properly. Then, the team will have 5 seconds for manual intervention. Typically, this will only mean dumping the balls in a hopper and turning the controller on, but it could also include other forms of intervention (e.g. pulling a lever to load several springs for firing projectiles). Next, the machine will be allowed to run for 15 seconds in order to sort the balls or prepare for firing.
NOTE: target tracking should not occur during this time.  The TA computer will send a serial command to the shooter to trigger the start of each test.

Static Test
In this test, only one stationary target will be used. The target will be at a random location within the shooting area, unknown to the machine at the beginning of the test. Each machine will have 20 seconds to locate the target, aim the shooter, and fire 6 projectiles at the target.
Performance Metric: Successfully hit the target with 5/6 shots in 20 seconds or less

Dynamic Test
This test consists of 4 trials, each lasting 40 seconds, and up to 6 balls (shots) per trial. During a trial, two targets remain stationary while the third target moves. In a “perfect” trial, you would hit each of the three targets with two shots within the time limit. The machine may shoot at targets in any order and at each target as many times as desired, but will only receive credit for up to two hits of a given target per trial. You may, for example, keep firing at a static target until you hit it twice before moving on to another target.
Performance Metric: Successfully hit 12/16 static targets and 4/8 dynamic targets in 4 trials of 40 seconds or less.