Gravity Vehicle

Questions? Send me an email!

nathan.smith@icsd.k12.ny.us

Overview:

The objective of this event is to build a gravity-powered vehicle and a ramp that will launch the car to a specific target 9 to 12 meters away accurately and quickly. This is a build event, so if you like engineering or building cool devices, this might be a good event for you.

Main requirements:

If you do not follow these requirements, the event supervisors can disqualify you. Some supervisors are chill, but it's much better to be safe. These are a few of the most important, but you should definitely read over the rules manual as well. (This is the 2020 rules manual. Most of the rules are staying the same for 2021, but read this with care.)

Vehicle:

• Weight less than 2 kg. This requirement is not that restrictive.

• Must have a dowel attached vertically to the very front. This is not a huge deal, but don't forget about it when creating your design.

Ramp:

• The ramp must be less than 50 centimeters in width and depth, and 100 centimeters in height. A big ramp is best, because the car will move faster and be able to reach the full 12 meters.

Release Mechanism:

• Must be activated by an unsharpened pencil

Scoring:

You want the lowest score given by this equation:

2 points / cm * distance from target + 1 point / sec * Run Time.

The run time is pretty consistent whatever you do, so you really want to minimize the distance. This is point-to-point distance, so being off horizontally will count against you. You are allowed two runs, and they will count the run with the lowest score.

Design:

The first thing you should do for all events, especially build events, is read the rules manual! (Again, this is the 2020 version.) Make sure you understand the requirements, restrictions, and scoring.

Before building anything, it is important to create a thorough design for both the ramp and the car. Looking up designs created by other teams in previous years can be very helpful. The most technical part of this event is creating the braking device that will allow you to stop the car at a specific point from 9 to 12 meters away. The simplest design involves a wingnut riding on a threaded axle. Because the wingnut cannot spin with the axle, it is forced to move down the axle until it pinches against the wheel, stopping the car. To calibrate it you move the wingnut the appropriate distance along the axle. Click here to see a video about how this works.

A second important design decision is the release mechanism. Again I recommend looking up past designs by other teams. The way I did it is I placed a hook at the back of the vehicle, and several hooks in line at the top of the ramp, so that the pencil would support the vehicle while resting on the hooks. To release the car you pull out the pencil quickly. There are a lot of different ways to create a release mechanism, and most will work, but it is important that it is consistent and will not jerk the vehicle off course.

It is much easier to plan first and build second than to build without planning, and have to redo something because it didn't work out the way you thought. (I learned this the hard way!) Plan out how the pieces of the car and the ramp will fit together and how they will work. This means you will probably have to start early; designing, building, calibrating, and testing a gravity vehicle from scratch takes a long time. (I learned this the hard way as well!)

Building:

You will probably want to meet outside of the normal Monday and Wednesday meeting times to work on building your gravity vehicle. Meet somewhere that has access to all of the materials and tools that you need: a good saw - jigsaws work well, wood, screws, a screwdriver, a wrench, a power drill, a good table, possibly a vise, and any other special building materials for your car or vehicle. It's possible that you could create a ramp and vehicle without these tools, but I wouldn't recommend it. Fewer, longer meetings for a couple hours are best. It takes a while to get set up, and there are always unforeseen problems. Finally, make sure to use screws wherever you can instead of glue. Screws make it easier to disassemble, and are sturdier.

Calibration:

Now that you have built your ramp and vehicle, you are going to have to see how to get it to go, and to make it stop at the right distance. At regionals and most invitationals, the distances range from 9 to 12 meters, at half meter intervals. This means you should be prepared for 9.0, 9.5, 10.0, 10.5, 11, 11.5, and 12.0 meters. Do some practice runs at different distances, and record your data in a spreadsheet, including how you calibrated it, the target distance, the distance from the vehicle to the target, run time, and any other variables you want to add. Using this data you can determine how you want to calibrate the braking system for each of the seven distances.

Practice setting up the ramp and the vehicle, calibrating it, and releasing it within the eight minute time frame.

Testing:

Congrats! You now have a working gravity vehicle! After this at competitions you just do exactly what you did when you practiced. The first run is valuable as a test. If the vehicle veers right, turn the ramp to the left. If it overshoots, adjust the braking system. If you do it right you should be guaranteed to get very close.

If you noticed any problems with your vehicle or ramp during the testing, or were penalized for anything, make sure to fix it before the next competition.