How to Determine the Speed of a CO2 Dragster

The quickest way to find a CO2 dragster’s speed is to measure how long it takes to travel a known distance and use the formula v = distance ÷ time; in practice, this is best done with electronic photogates or high‑speed video to capture precise timing. Below, we explain what “speed” means in this context, the most reliable measurement methods used in school competitions and labs, how to calculate both average and near‑instantaneous speeds, and how to improve accuracy. Note: the gas is carbon dioxide (CO2), not “C02.”

What “speed” means for CO2 dragsters

In competitions, you’ll often quote average speed over the full track (for example, 20 m) as v_avg = L ÷ t. Because a CO2 car accelerates rapidly and then coasts while drag increases, its instantaneous speed rises and then levels off; to estimate peak speed, you’ll need split times over shorter intervals, a radar reading, or high‑speed video analysis. State up front whether you’re reporting average track speed, split‑segment speed, or an estimated peak.

Practical ways to measure speed

Method 1: Electronic photogates (most reliable)

Photogates placed at known positions on the track provide millisecond‑level timing by detecting when the car breaks a light beam. This is the standard approach in many classroom setups and competitions.

• Use at least two gates: one near the start and one at the finish; optional gates at splits (e.g., 5 m, 10 m, 15 m) improve peak‑speed estimates.
• Calibrate the distance between gates with a tape measure; record to the nearest millimeter if possible.
• Trigger timing consistently (e.g., when the car’s nose breaks the first beam) and log the elapsed time to the next beam.
• Compute average speed for each interval as v = Δx ÷ Δt; the highest split speed approximates top speed.

Photogates minimize human reaction error and provide repeatable, competition‑grade timing. Additional split gates help isolate acceleration versus top‑end performance.

Method 2: High‑speed video timing

High‑speed video lets you measure times across known markers on the track when photogates aren’t available.

• Place contrasting distance markers (e.g., every 1 or 2 m) along the lane and measure their spacing accurately.
• Record at a high frame rate (at least 240 fps; 480–1000 fps is better) with the camera perpendicular to the track to reduce parallax.
• In editing software, note the frame numbers when the car’s nose passes each marker; time is frames ÷ frame rate.
• Compute speeds for each segment with v = Δx ÷ Δt; smooth noisy data by averaging adjacent segments if needed.

While less precise than photogates at low frame rates, high‑speed video is versatile and provides visual verification of passes and alignment.

Method 3: Handheld radar or lidar gun

Sports radar/lidar guns can read instantaneous speed without timing gates, but require careful aiming and adequate distance.

• Position the gun down the lane, aligned with the car’s direction, and start reading after launch wobble.
• Take multiple passes and record the maximum stable reading as peak speed.
• Verify gun accuracy with a known moving object or manufacturer calibration mode.

Radar is great for peak speed snapshots, but it won’t give you total run time or acceleration data by itself.

Method 4: Onboard sensors (advanced)

Lightweight onboard sensors can estimate speed if external equipment is limited.

• Use a tiny wheel encoder (knowing wheel circumference) or an IMU fused with a pressure/drag model.
• Log data at high frequency (≥200 Hz) and correct for wheel slip and encoder resolution.
• Validate onboard estimates against at least one external timing method.

Onboard systems can reveal acceleration curves but add complexity and weight; they are best for development rather than official timing.

How to calculate average and instantaneous speeds

Average speed over the full track length L is v_avg = L ÷ t_total. For example, if a 20.0 m track time is 0.90 s, v_avg ≈ 22.2 m/s (≈49.7 mph). To approximate instantaneous speed, break the track into shorter distances and compute v_segment = Δx ÷ Δt; the fastest segment is a good proxy for peak speed, though true peak likely occurs within that segment.

A quick, repeatable measurement procedure

The following steps outline a simple, dependable workflow using photogates or high‑speed video to determine speed accurately.

1. Measure the track: Confirm total distance (e.g., 20.000 m) and mark split points (e.g., every 5.000 m).
2. Set up timing: Install photogates at start/finish and at splits, or place visible markers for video analysis.
3. Calibrate: Verify gate spacing and timing system; for video, verify frame rate and field of view.
4. Run multiple trials: Perform at least three clean runs under similar conditions; discard obvious outliers.
5. Compute speeds: For each interval, compute v = Δx ÷ Δt; report full‑track average and fastest split (peak proxy).
6. Report conditions: Note ambient temperature, air pressure (altitude), and any wind, as these affect drag and CO2 thrust.

This process yields robust, comparable results and helps diagnose setup changes by separating launch, mid‑track, and top‑end performance.

Understanding a theoretical estimate (optional)

You can estimate expected performance by balancing thrust from the CO2 cartridge against resistive forces: aerodynamic drag (0.5 × air density × drag coefficient × frontal area × v²) and rolling/frictional losses. A simple time‑step model integrates acceleration a = (thrust − drag − rolling) ÷ mass to predict a velocity curve. While insightful for design, real cartridges vary in pressure and discharge rate, so direct measurement is still required for official speeds.

Accuracy and uncertainty: what affects your numbers

These are the common sources of error and how they can influence measured speed.

• Timing resolution: Gate or video frame quantization introduces ±1 tick/frame uncertainty; shorter intervals amplify relative error.
• Distance calibration: A 1 cm error over 1 m is a 1% speed error; measure and level the track carefully.
• Trigger definition: Always measure the same reference point (e.g., nose breaking the beam) to avoid length‑dependent timing shifts.
• Parallax and camera angle: Off‑axis video skews marker crossings; keep the lens perpendicular and at mid‑height.
• Environmental factors: Wind, temperature, and altitude change air density and thrust, altering both time and peak speed.
• Lane hardware: Tether string friction, wheel alignment, and bearing quality change rolling resistance and consistency.

Quantifying these uncertainties (for example, reporting v = 23.4 ± 0.4 m/s) improves the credibility and repeatability of your results.

Example: computing average and peak‑proxy speeds

Suppose a 20.000 m run has the following split times from calibrated photogates: 0–10 m in 0.55 s and 10–20 m in 0.35 s. Then the 0–10 m average speed is 10 ÷ 0.55 ≈ 18.2 m/s (≈40.7 mph), the 10–20 m average speed is 10 ÷ 0.35 ≈ 28.6 m/s (≈64.0 mph), and the full‑track average is 20 ÷ 0.90 ≈ 22.2 m/s (≈49.7 mph). The 28.6 m/s split suggests peak speed near the second half of the run; true peak likely exceeds that by a small margin within that interval.

Frequently used formulas and conversions

Keep these simple relations handy when reporting or comparing results.

• Average speed: v = distance ÷ time
• Segment speed: v_segment = Δx ÷ Δt
• m/s to km/h: multiply by 3.6
• m/s to mph: multiply by 2.237

Using consistent units and clear definitions avoids confusion across teams and events.

Safety and compliance notes

CO2 cartridges release gas rapidly; ensure your setup is safe and aligned with school or event rules.

• Use approved puncture mechanisms and shields; never point a charged car at people.
• Secure the lane/tether system and check for obstructions before each run.
• Follow competition specifications for car mass, cartridge size, and launch procedures to keep results comparable.

Proper safety practices protect participants and equipment and help maintain reliable, rule‑compliant measurements.

Summary

To determine a CO2 dragster’s speed, measure the time over a precisely known distance and compute v = distance ÷ time, ideally with photogates or high‑speed video. Report full‑track average speed and, if possible, split‑segment speeds to estimate peak velocity. Calibrate distances, standardize triggers, and account for environmental conditions to minimize error and ensure repeatable, competition‑ready results.

What are the four main factors that influence the speed of a CO2 dragster?

Here are some of the principal forces involved:

• Mass: Obviously, this is how large and heavy the car is.
• Thrust: The gas escaping from the CO2 cartridge in the car.
• Friction: The second most important fact you’ll face.
• Drag: Here’s where aerodynamics come into play.

What is the average speed of a CO2 dragster?

Race results showed an average speed of 10.13m/s or 36.47km/hr over 3 trials, placing the dragster 5th out of 20 in class.

What makes a fast CO2 dragster?

Simply put, the less weight your dragster has, the faster it will go. This is the most important factor that will figure into your design. Keep it light! Thrust: The gas escaping from the CO2 cartridge in the car.

How do you determine the speed of the CO2 dragster?

Using a Pitsco launch and timing system, test the dragster using an 8-gram CO2 cartridge and time it for a 20-meter distance. The average velocity is calculated using the formula velocity equals distance (meters) divided by time (seconds), or v = d/t.
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