Decision: Type of Rangefinder for Obstacle Detection

\uD83D\uDCDA Relevant data

This follows from the discussion during the 2023-09-24 Conops Brief for the 2024 AEAC Student UAS competition brief.

\uD83D\uDCD8 Background

Our end-goal is to provide safety for the drone and it’s payload when landing in a LZ-C, which is a BVLOS landing zone with overhangs and obstacles.

Existing support

Ardupilot has native support for both object detection, as well as multiple lidar sensors. Using information synthesized from up to 10 sectors (8 around, 1 top, 1 bottom), and known INS parameters, the vehicle is able to stop at a predetermined distance from the fence regardless of the speed of the vehicle. This service is provided in all guided flight modes, as well as altitude hold.

When data is not received from all 8 sectors, empty sectors are filled in with distance from an adjacent sector (if available).

In regular operation, we only anticipate approaching obstacles facing forwards, and so sideways and rear-facing object detection is not as important.

Multiple kinds of rangefinders are supported within ardupilot, which can be found within copter documentation: Rangefinders (landing page) — Copter documentation (ardupilot.org).

\uD83C\uDF08 360 vs Unidirectional

🚨 Omnidirectional Sensor Options

❗ Unidirectional Sensor Options

Since the list is incredibly exhaustive, I have pre-selected sensors which meet the minimum range (~ 8m) and cost requirements (< 100 per part).

Sensors which have not been included are:

• Ainstein US-D1: Cost (600 each)

• Attollo Wasp-200: Cost (530 each)

• TF-Luna: Range (outdoors range of 3m only)

• GY-US42v2: Range (indoor only and only 4m)

• Hondex HE-8S: Use case (this is an underwater sonar)

• HC-SR04: Range (2m indoor only)

• JSN-SR04T: Consistency/reliability ( poor )

• Leddar One Lidar: Sourcing (impossible to find)

• Leddar Vu8: Sourcing (impossible to find) & price (1100)

• Lightware SF1/11/20/02 (price, sourcing)

• Maxbotix Sonar: Range (7m), use (indoor)

• ST VL53L0X/VL53L1X: Range (2/4m)

\uD83C\uDF1F Recommendations

Pending review, the recommended solution is to use 3 Benewake TF-Mini-S series sensors or 1 Lightware SF45-B Sensor. Should the need present itself, the SF45-B may be augmented by downwards and upwards facing rangefinders. The following considerations should be reviewed:

1. Weight

3*5 = 15g. Even considering the weight (~4g per) of the CAN interfacing boards, the weight of the benewake sensors comes out to around the same weight as the omnidirectional lidar (27 vs 59 grams), not including the non-negligible wire weight that the unidirectional sensors will have to maintain.

Both options presented here are significantly lighter than any alternatives.

2. Packaging/form factor

Both options presented here are slimmer/sleeker than the others. Unidirectional sensors may be similar to each other, but the SF45 is significantly sleeker and easier to integrate than other sensors.

3. Cost

The unidirectional system would total to around 180, while the omnidirectional system would be a flat price of around 450 cad. Both costs are still significantly lower than other alternatives, with the possibility of using superior sensors unidirectionally, or more sensors unidirectionally, to compensate for the relatively worse performance of the TF-Mini-S.

✅ Outcome

🗒️ Changelog