Laser Rangefinder for UAV Gimbals: Selection Guide
A UAV gimbal is the most demanding place to put a laser rangefinder. The payload is mass-limited, power-limited and thermally constrained, while the platform moves in ways that a turret-mounted module never has to tolerate.
Why gimbal integration is different
- Every gram is a flight cost. Payload mass trades directly against endurance. A 680 g module plus its thermal path can be the difference between two sorties and three.
- Stabilisation sets divergence. A gimbal with 0.2 mrad of residual jitter cannot hold a 0.15 mrad beam on a small target at 10 km. The beam walks off.
- Cooling is passive. There is no forced air on a small UAV. Heat must conduct into the gimbal structure, which is itself thermally isolated by the slip ring.
- Power is shared. Data link, gimbal motors, EO sensor and laser all draw from the same battery.
Module options by UAV class
| UAV class | Typical module | Mass | Pulse energy | Divergence |
|---|---|---|---|---|
| Small / tactical | LDR20K1 | ≤ 290 g | ≥ 20 mJ | ≤ 0.6 mrad |
| Tactical | LDR25K1 | ≤ 380 g | ≥ 25 mJ | not published |
| Medium endurance | LDR40K1 / LDR40K3 | 420–460 g | ≥ 40 mJ | not published |
| Long endurance, 10 km class | LDR60K1 / LDR80K1 | ≤ 680 g | ≥ 60 mJ | ≤ 0.3 mrad |
| 15 km class, large gimbal | LDR80K2 | ≤ 850 g | not published | ≤ 0.15 mrad |
The mass you forget
A 290 g module does not add 290 g to the aircraft. Add:
- mounting bracket and datum plate
- thermal strap or cold plate
- harness with shielded twisted pairs through the slip ring
- power conditioning if the bus is not in the module's range
- window with coating, and heating if condensation is a risk
A realistic multiplier is 1.5–2× the bare module mass. Design the mass budget with that in mind.
Divergence vs gimbal quality
Match divergence to how well the gimbal can hold a line of sight:
| Gimbal residual jitter | Sensible divergence |
|---|---|
| < 0.1 mrad | 0.15 mrad |
| 0.1–0.3 mrad | 0.3 mrad |
| > 0.3 mrad | 0.6 mrad |
Buying a 0.15 mrad module for a gimbal with 0.5 mrad jitter wastes both money and the energy advantage.
Ranging and designation on the same gimbal
Most ERDI modules combine both channels, which matters on a UAV: one module, one mount, one harness, one cooling path. The trade is that designation imposes a duty cycle — the module cannot designate continuously, and the gimbal must be pointing at the target for the whole cycle.
Typical qualified cycles for long-range modules are 16 s on / 9 s off (short duration) and 60 s on / 60 s off (long duration). If the concept of operations does not fit those windows, the thermal design must change.
Interface on a UAV
RS-422 is the common choice for the direct link to the payload computer: deterministic, differential, no bus arbitration. CAN is used when the module must join a vehicle bus. For harnesses passing a slip ring, budget for signal integrity — a slip ring adds noise and intermittent contact.
Your software should treat a missing reply as "unknown", never as "range = 0". See interface selection.
Frequently asked questions
What is the lightest ERDI laser rangefinder module?
The LDR20K1 at ≤ 290 g, with ≥ 20 mJ pulse energy and ≤ 0.6 mrad divergence.
Can a UAV rangefinder also designate targets?
Yes — most ERDI 1064 nm modules combine ranging and designation. Designation adds a duty-cycle constraint and a thermal load.
How much range can a small UAV achieve?
With a 20–25 mJ module and a stable gimbal, typically 3–5 km against a vehicle-sized target in clear air. Longer range needs more energy and more mass.
Do I need a stabilised gimbal for a tight beam?
Yes. A 0.15 mrad beam on an unstabilised mount will miss at long range. Match divergence to jitter.
See the UAV and EO/IR payload collection or read the SWaP trade-off guide.