Battery Buggy

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Battery Buggy

Type Engineering
Category Build
Forum Threads
Division B Results
1st Slauson Middle School
2nd Solon Middle School
3rd Kraemer Middle School

Battery Buggy is a Division B vehicle event. It was first run in 1999, and was held every year until 2003, when it was replaced with Robo-Billiards. Battery Buggy was then run as an event in 2010 and 2011, before being brought back for the 2018 and 2019 seasons. It requires participants to design and build a moving, battery-powered vehicle capable of traveling a certain distance and stopping as close to the ending dot at that distance as possible. The device must meet several parameters regarding size, total power used, types of power used (power must be electrical), and safety restrictions.

The Competition

DISCLAIMER: Opinions and interpretations of rules on this site are not official. The only place for official rules changes and FAQ is soinc.org.

Track-Layout-Battery-Buggy-2019.png

At the event, event supervisors will designate a target distance between 9 and 12 meters away from the starting point. The distance will be in 50.0 cm intervals at the regional level, 10.0 cm intervals for state and 1.0 cm intervals for national tournaments. The object of the event is for the vehicle to get as close to the target distance as possible and come to a complete stop. The 2011 rules also required the buggy to curve around a bucket placed in the center of the track. All teams will have the same target distance at a given event. In order to be placed in the highest possible tier and avoid incurring penalty points, participants must impound both their vehicle and a completed practice log at a disclosed location prior to the event.

Participants will be given 8 minutes to complete two runs, as well as perform a variety of adjustments to the vehicle. AC power outlets will not be available for the duration. Participants may measure or clean the track, or use precision measuring tools to align the vehicle. Alignment tools mounted to the vehicle may remain on the vehicle during runs, but any placed on the track must be removed before beginning a run. The 2018 and 2019 rules also introduce a bonus, which subtracts points from the total score. Participants must declare that they will attempt the bonus before each run begins.

To begin a run, participants place their buggy on the track so that the tip of the dowel (known as the measuring point) is aligned with the starting point. Participants should announce to the event supervisor that a run is about to begin, at which point the buggy should be activated with the eraser of an unsharpened #2 pencil. This should be provided by the event supervisor. Teams may not touch the vehicle from the time the run is started until the event supervisor says it is okay to do so - this includes flipping a switch or pushing the vehicle to start it. Participants must also stay behind the starting point, as following the buggy results in a competition violation.

A run begins if the vehicle moves after the switch is pressed. However, failed runs can occur if the vehicle moves backwards, it starts before the supervisor is ready, the vehicle does not stop using its own braking system, or if the vehicle does not reach the 0.5 meter line. A failed run can also occur if participants pick up their buggy before it is measured. Timing begins as soon as the vehicle passes the 0.5 meter line, and ends as soon as it passes the 8.5 meter line. After the vehicle stops, the event supervisor will measure the distance from the measuring point to the target point. Measuring time does not count towards the 8 minutes that participants are given to complete their runs. After the time and distance are confirmed, the event supervisor should give the participants permission to retrieve their buggy. Two runs are given, with the highest score being used for ranking.

In the 2019 season, teams may also declare that they are going for a bonus before beginning a run. Two weighted cans with diameters of 7 to 8 cm are placed on the field, located on a bonus line halfway between the starting point and the target point. This bonus line is perpendicular to a center line, 1 meter to the left when facing the target point (see the figure on the left for the 2019 track layout). The outer can will always be placed on the bonus line, while the inner can may be moved by the participants up to 100 cm away from the outer can. The inner distance is used for this measurement. The lower the distance between the two cans, the better bonus is given to the team. All parts of the vehicle must pass between the cans for it to count, and if the vehicle moves the cans no points will be awarded. Cans may be removed from the field if the participants do not wish to attempt the bonus. The 2018 season offered a center line bonus, which teams could earn if the center line of the track remained between the widest wheelbase for the distance between the starting point and the target point. If the vehicle went off the center line after passing the target point, the bonus would still be awarded.

Once competition is finished or the eight minutes are up, the event supervisor will review the data and penalties recorded with the competing team. If a run is started before the 8 minute mark is up and extends past the 8 minute mark, it will be allowed to run to completion before scoring. Teams who would like to appeal their score must leave their vehicle with the event supervisor.

Parts of a Buggy

Wooden Chassis

Chassis

Metal Chassis

The chassis is the main body of the vehicle, on which the wheels, braking system, and electrical components are mounted. Common choices for a chassis are wood, plastic, or metal, but any rigid material that can be connected into a tight frame will do. Erector sets also work fine for a chassis.

While any material could be used, but it's best to use the lightest material feasible. Be cautious with thin pieces of wood due to warping, which could negatively affect the vehicle's trajectory, causing it to turn. It should also be easy to drill holes for mounting components.

Wheels

Cars can be three- or four-wheeled, but four wheels are recommended. Wheels collectively must fit within a 30 cm by 60 cm space of any height throughout the entire run, but axles and other parts of the vehicle may extend beyond these parameters. A larger diameter wheel requires a higher geared motor, but it revolves fewer times to make the buggy go the specified distance. They make the buggy go faster, but are heavier. Conversely, smaller wheels are slower but lighter. Smaller wheels also revolve more frequently, and require lower geared motors. CDs with balloons wrapped around them are a common choice for wheels, as they are readily available and the balloons provide extra grip. Robotics-oriented vendors such as BaneBots and AndyMark have also been used for vehicles. These wheels range both in softness and size, providing a wide variety for competitors to choose from.

Threaded rods are an accessible solution for axles. These rods provide a solution for brakes, and are also typically easy to attach wheels to. Threaded rods can be found at most hardware stores.

Dowel

For 2019, a 1/4" or larger round wooden dowel is required to be used for measurement. The dowel should be the leading part of the buggy and should be placed at the front of the vehicle positioned approximately perpendicular to the floor, such that there is 1 cm or less between the bottom of the dowel and the floor. It should also be at least 20 cm long. The dowel attachment piece cannot extend more than 0.5 cm beyond the front of the dowel.

Care must be taken to make sure that the dowel does not detach during runs. A detachment would result in a construction violation, leading to the team being placed in Tier 3.

Electrical System

Batteries

In the 2019 version of the rules, energy used by the vehicle must be stored by up to eight 1.2 to 1.5 volt AA batteries that are individually labeled by the manufacturer. Normal dry cells (primary cells) can be fairly expensive over time, but while rechargeable batteries (secondary cells) require a greater initial outlay, they can reduce costs significantly over time. Any type of battery can be used except for any lithium or lead acid batteries - if these batteries are used on a vehicle teams are not permitted to run and will instead receive participation points. Nickle metal hydride (NiMH) and nickle-cadmium (NiCad) cells may be used, as well as other varieties of primary cells such as alkaline cells. Batteries may not be installed until immediately prior to a run.

Battery holders or boxes are also allowed, as long as the individual labels can be inspected during impound. Battery holders often take the form of plastic boxes with contacts on either end that the batteries are inserted into. They typically have bare wires coming out of one side so that the holder can be attacked to any circuitry that the batteries need to power. They can be ordered from a variety of online retailers.

Switches

The vehicle circuit above uses separate start and stop switches. A common slide switch, located near the center of the chassis, is used to start the vehicle. This type of switch can require significant force to actuate and may cause the vehicle to move before it is actuated. It may pay to investigate other options that take less force. A lever switch (sometimes referred to as a micro switch) located near the wheel at one end of the threaded axle is used for the stop switch. As the wheels turn, the wing nut travels on the axle until it contacts the lever on the switch and depresses it to turn off the motor and stop the vehicle. Because of the way this switch is being used, it is useful to use a latching switch. These switches are available from Radio Shack and many other electronic/robotic suppliers. Make sure that the switch is also compliant with the rules.

Wires

Almost any electrical wire can be used. A common source is recycled 4-conductor telephone wire. It can be separated into individual wires by removing the outer cover. Solid wire (has only 1 large strand of wire inside) is stiffer and easier to work with, but breaks sooner when flexed. Stranded wire (has several thin strands of wire inside) is more difficult to work with, but doesn't break as easily when flexed.

Motors

Motors determine the voltage and current capacity needed from the batteries and must be mechanically compatible with the transmission/gearbox used. Motors are usually supplied as part of commercially available transmissions/gearboxes, such as Tamiya gearboxes. Another source for gearboxes/transmissions is old (or not so old) battery operated screwdrivers. The batteries may even be recycled if they are still good. The motor should be rated between 6-12 volts as the maximum battery voltage is 8 volts. This may be a good motor to start with.

(Note: It is possible to recycle the entire rear axle with transmission and wheels from an inexpensive Radio Control or RC vehicle.)

Braking

Braking is an essential part of adjusting the distance a buggy travels. A wing nut brake makes use of a threaded axle and a wing nut. As the axle turns, a wing nut travels along its length. The wing nut will reach a point where it cannot travel anymore, restricting the axle's movement.

SC-brake2diag.gifSC-brake2.gif
EVcircuitTransparent.png

However, a wing nut alone does not remove power from the drive motor, which is necessary to prevent the motor from stalling. A stalled motor can burn out and melt wires, potentially damaging the vehicle or the competitors. To avoid this, the wingnut can hit (and lock against) a momentary switch. If the motor is in a Normally Closed circuit (as it is in the diagram to the right), the motor will be turned off when the wingnut presses the switch. The circuit may also be wired by adding a wire that runs between NO and the (-) side of the motor so that it acts as an eddy current brake and resists further rotation. These measures should provide an immediate and effective braking system that can be reliably calibrated.

Dynamic/Regenerative Braking

Dynamicbraking.gif

This style of braking uses the drive motor as a dynamo (generator) to slow the vehicle. When the electrical current is turned off, the motor/vehicle begins to coast and acts as a generator. The force required to turn the generator is proportional to the current generated. When the generator is connected to an open circuit (infinite resistance), no current flows and the force needed to keep the generator rotating is only that needed to overcome friction. If the generator output terminals are connected together with a low resistance connection (short) the current in the circuit increases, which in turn requires more force to turn the generator. This acts as a brake to slow the vehicle.

For more information on braking, see Scrambler#Brakes. Note that in the 2019 rules, no part of the vehicle other than the wheels may contact the floor.




Turning

The 2019 version of the rules has an optional bonus, in which the vehicle has to pass between two cans placed on the track. One can is placed on a bonus line halfway between the starting point and the target point, 1 meter away from the center line. The second can may be moved by the participant, up to 1 meter away from the first can. To have some way of turning, the back axle can be adjusted at an angle to the front and the device can be turned at the starting point. The device should be measured against a straight line from the starting point to the target point. Turning may also be implemented by using a threaded rod system, similar to the method of braking discussed above. Using a sighting device is not necessary, but it can allow for a more precise turn.

Practice Log

Because of the many variables involved in running the car, much testing must be done to figure out exactly what to do, since theoretical calculations do not always match real life. In the 2018 and 2019 version of the rules, a practice log was required to be impounded with the vehicle before the event. In the 2018 rules, a practice log required at least three parameters, which must include time, distance and any additional parameter. For 2019, time and distance were still required but wheel settings and bonus can distances (if applicable) should also be recorded. One or more vehicle parameters should be modified throughout the practice log, and at least 10 practice runs are required for both versions of the rules.

Scoring

The lowest score wins, and negative scores are possible. The lowest score of the two runs is used in all cases. Scoring is calculated based on three factors:

  • Run time: The time it takes for the buggy to travel from the 0.5 m line until it either stops or passes the 8.5 m line.
  • Distance score: A point to point measurement from the measurement point (dowel tip) to the target point, measured to the nearest 0.1 cm. The distance score is multiplied by two before being added to the final score.
  • Bonus: For the 2019 season, the formula for bonus points is -0.5 * (110-n), where n is the inside distance between the two cans. In the 2018 season, the bonus was a flat -25 points.

Scoring is calculated by adding together the run time, distance score multiplied by two, and any bonus points. Penalty points may also be added to a team's score - failure to impound a practice log will incur a 500 point penalty and an incomplete practice log will earn a 250 point penalty. However, the practice log does not impact what tier a vehicle is placed in. Tiers for this event are as follows:

  • Tier 1: A run with no violations.
  • Tier 2: A run with competition violations, such as following the buggy down the track or stopping before the vehicle passes the 8.5 m line.
  • Tier 3: A run with construction violations, such as the dowel detaching during a run.
  • Tier 4: A run where the vehicle is not impounded before the event.

Ties are broken using the lowest bonus distance first, followed by the lowest distance score, time score and lowest time of the run not used.

Nationals Scores

2018 Nationals Results
Place School Distance (cm) Time Score Track Length
1st Solon Middle School 1.5 2.309 -14.382 10.94m
2nd Kennedy Middle School 0.9 3.552 -14.296 10.94m
3rd Piedmont Middle School 1.7 3.628 -10.944 10.94m
4th Thomas Jefferson Middle School 2.1 3.469 -9.662 10.94m
5th Community Middle School 3.3 2.068^ -7.664 10.94m
6th Chippewa Middle School 2.3 4.306 -7.188 10.94m
7th Fred J. Carnage Middle School 2.9 3.907 -5.586 10.94m
8th Meads Mill Middle School 3.5 3.276 -4.448 10.94m
9th Hamilton Middle School 3.6 3.301 -3.998 10.94m
10th Springhouse Middle School 4.5 2.306 -2.388 10.94m

^: Fastest Run at nationals.

2019 Nationals Results
Place School Distance (cm) Time Bonus (cm) Score Track Length
1st Slauson Middle School 4.4 3.029 15.5 -35.421 11.28m
2nd Solon Middle School 2.0 2.978 28.0 -34.022 11.28m
3rd Kraemer Middle School 1.9 8.210 18.0 -33.990 11.28m
4th Community Middle School 4.7 2.716 20.0 -32.884 11.28m
5th Longfellow Middle School 4.7 3.663 18.5 -32.687 11.28m
6th Springhouse Middle School 3.5 2.443 26.5 -32.307 11.28m
7th Harlan Rowe Middle School 3.5 5.826 25.0 -29.674 11.28m
8th William Diamond Middle School 2.3 4.689 35.0 -28.211 11.28m
9th Paul J. Gelinas Junior High School 5.8 5.745 20.0 -27.655 11.28m
10th Kennedy Middle School 8.1 5.768 22.8 -21.632 11.28m

Links

MadCow2357's Battery Buggy Guide
Microswitches
Note: Electric Vehicle, a Division C event, is very similar to Battery Buggy.