Library / Driveline and transmission / DRV-19
Driveline and transmission
Track-pitch excitation frequency
Frequency at which track links pass a point on the ground, equal to the vehicle speed divided by the track pitch.
- Ref
- DRV-19
- Rev
- v1
- Field
- Driveline and transmission
- Result
- ftrack [Hz]
Links pass a point on the ground at the vehicle’s speed divided by the track pitch, so ftrack ≈ v/pt, a main source of vibration in a tracked vehicle. It uses the vehicle speed with negligible slip. The speed is entered in km/h and converted to m/s inside the formula. The sprocket’s tooth-meshing frequency should instead use the actual rotational speed of the sprocket. A 20 km/h speed over a 0.15 m pitch gives 37.04 Hz.
Frequency at which track links pass a point on the ground, equal to the vehicle speed divided by the track pitch. It is a main source of vibration in a tracked vehicle and rises in direct proportion to speed.
Calculator
- Vehicle speed in m/s5.556 m/s
- Period between link passes27 ms
What drives the result
Each variable is moved across its typical range while the others stay at the values above. The longest bar is the key driver.
- At 20 km/h on 0.15 m pitch links, a link passes every 27 ms, which is 37.04 Hz. The frequency rises in proportion to speed: at 40 km/h it is 74.07 Hz.
- If a hull or seat resonance sits near 37 Hz, 20 km/h is the speed to avoid. Whole-body vibration sensitivity is greatest below about 20 Hz, so higher harmonics matter more for equipment than for people.
Chart data as tables
Ranked variables
| Variable | Typical range | Lowest result | Highest result | Swing (Hz) | Local step | Change in result |
|---|---|---|---|---|---|---|
| v Vehicle speed | 5 to 70 km/h | 9.259 | 129.6 | 120.4 | +10% | +10 % |
| pt Track pitch | 0.08 to 0.3 m | 18.52 | 69.44 | 50.93 | +10% | −9.09 % |
Sweep of Vehicle speed
| Vehicle speed (km/h) | Link passing frequency (Hz) |
|---|---|
| 5 | 9.259 |
| 13.13 | 24.31 |
| 21.25 | 39.35 |
| 29.38 | 54.4 |
| 37.5 | 69.44 |
| 45.63 | 84.49 |
| 53.75 | 99.54 |
| 61.88 | 114.6 |
| 70 | 129.6 |
Sweep one variable
Variables and how each one contributes
Link passing frequency
What the equation gives you. Everything else feeds it.
Vehicle speed
The vehicle speed, in km/h. Raises the frequency in proportion. Raising it by 10 % (to 22) moves the result by +10 %, from 37.04 to 40.74 Hz.
Track pitch
The track pitch, the distance between corresponding points on neighbouring links, in m. Lowers the frequency in inverse proportion: longer links pass at a lower rate. Raising it by 10 % (to 0.165) moves the result by −9.09 %, from 37.04 to 33.67 Hz.
Worked example with the values above
- Convert the speed: 20 km/h ÷ 3.6 = 5.556 m/s.
- Divide by the pitch: 5.556 / 0.15.
- ftrack ≈ 37.04 Hz.
Assumptions and limits
- Negligible track slip, so link speed equals vehicle speed.
- A uniform pitch along the track.
Common mistakes
- Entering the speed in m/s while the formula expects km/h.
- Confusing the track pitch with the distance between road wheels.
Statistics and uncertainty
Track slip of a few per cent on soft ground reduces the actual speed of the links relative to the ground, so the frequency based on ground speed is a little high. For sprocket meshing use the measured sprocket speed.
Where it is used
- Predicting the dominant vibration frequency of a tracked vehicle.
- Finding speeds at which the link rate meets a hull or seat resonance.
Maths you need
- Frequency and period: f = 1/T
- Speed unit conversion: 1 m/s = 3.6 km/h