Draft Decision: Better RTK
- Ayoung Eun
- Yashashwin Karthikeyan
Status | In process |
|---|---|
Impact | High |
Driver | @Ayoung Eun |
Approver |
|
Contributors | @Derek Tang |
Informed | Not yet informed. |
Due date | 11-22-2023 |
Resources | |
References | https://discord.com/channels/776618956638388305/1157058056631369729 |
Relevant data
This decision matrix is derived from this document : Better RTK GPUS support for Ardupilot
Background
L1, L2 and L5
Our end-goal is to be able to locate our drone while the module maintains safe, consistent fixes.
Most RTK solutions support L1/L2. The L1 signal uses the frequency 1575.42 MHz, while L2 signal uses the frequency of 1227.60 MHz. Lower frequencies allow the signal to travel through obstacles such as cloud cover, trees, and buildings better. However, since L1 is the oldest signal out in the field of GPS, one can say that even the cheapest GPS is capable of supporting it. L5 is lot newer than L1 and L2. It is the most advanced signal but not every GPS supports it.
It is important to keep in mind that when choosing GPSs for base station and rover (drone), we need to ensure both support the same frequency bands. If, for example, drone supports L1, L5 and base supports only L1; we are effectively handicapping the drone to just L1. RTK requires common frequency bands for performing the computation. If using L1, L2 on drone and L1 ,L2 on base; both the bands are tracked by the drone and RTK will be able to perform at dual frequency and better performance.
Existing support
Currently our drone is supported by NEO M8 GPS manufactured by Team Blacksheep. We are currently attempting to source another GPS from VectorNav for a VN-200 rugged dev kit through sponsorship.
NEO vs PX
| M8P | F9P |
|---|---|---|
Description | single-banded (L1), M8P module uses M8 positioning engine and is able to support Time Kinematic (RTK) technology. | Dual banded (L1, L2), F9P module uses F9 positioning engine. which is newer than M8, and is able to support Time Kinematic (RTK) technology. |
Pros and cons | Cheaper Easier to find alternatives Incorrect position compared to F9P | Resolves RTK FIXED within seconds Better position hold performance Expensive |
M8P vs F9P
| M8P | F9P |
|---|---|---|
Description | single-banded (L1), M8P module uses M8 positioning engine and is able to support Time Kinematic (RTK) technology. | Dual banded (L1, L2), F9P module uses F9 positioning engine. which is newer than M8, and is able to support Time Kinematic (RTK) technology. |
Pros and cons | Cheaper Easier to find alternatives Incorrect position compared to F9P | Resolves RTK FIXED within seconds Better position hold performance Expensive |
M8P Options & D9S
Buy link / datasheet | NEO M8P | NEO D9S |
|---|---|---|
Product Page |
| |
Reliability | L1 only | All L-bands However, Rover Only & Less community experience. |
Cost (CAD) | $129-199 | $48.85 |
Size and Weight | 12.2 x 16.0 x 2.4 mm, 1.6 g | 12.2 x 16.0 x 2.4 mm, 1.6 g |
Position Accuracy | 0.025 m + 1 ppm CEP | Undocumented |
Convergence time | < 60 s Cold start 26s - 29s | Undocumented |
VSupply | 2.7 V to 3.6 V | 2.7 V to 3.6 V |
Interfaces | Already have driver | Driver needed. |
Weatherproof? | −40 °C to +85 °C | −40 °C to +85 °C Model B −40 °C to +105 °C Model A |
F9P Options
| NEO F9P | ZED F9P | ZED F9R |
|---|---|---|---|
Product page | https://www.u-blox.com/en/product/neo-f9p-module?legacy=Current#Product-Selection |
| |
Cost (CAD) | $350 | $129 | $150-220 |
Reliability | L1, L5 | L1, L5 | L1, L2 Rover only |
Size and Weight | 12 x 16 x 3.6 mm, 1.25g | 17 x 22 x 2.4 mm, 2g | 17 x 22 x 2.4 mm, 2g |
Position Accuracy | 0.01 m + 1 ppm CEP | 0.01 m + 1 ppm CEP | < 0.01 m + 1 ppm CEP |
Convergence time | < 10 s Cold start 27s - 37s | < 10 s Cold start 25s - 30s | < 10 s Cold start 24 s - 28s |
VSupply | 2.7 V to 3.6 V | 2.7 V to 3.6 V | 2.7 V to 3.6 V |
Interface | Driver needed. | Driver needed. | Driver needed. |
Weatherproof? | −40 °C to +85 °C | −40 °C to +85 °C | −40 °C to +85 °C |
| NEO F9P | PX1172RH-HAT |
|---|---|---|
Product page | https://www.u-blox.com/en/product/neo-f9p-module?legacy=Current#Product-Selection *Product including NEO-F9P and is compatible with Ardupilot usually ranges between 300-400$ | *Needs to buy antenna separately. Antenna is about 50$, 154 grams. Supply voltage 3V-12V. https://navspark.mybigcommerce.com/multi-frequency-high-precision-antenna/ |
Cost (CAD) | $350 Pricier than PX1172RH | $190 |
Reliability | L1, L5 | L1, L2 L5 performs better with obstacles and produces less noises |
Size and Weight | 12 x 16 x 3.6 mm, 1.25g | 17 mm x 22 mm x 2.9 mm, 1.7g Bigger and Heavier |
Position Accuracy | 0.01 m + 1 ppm CEP | 0.01 m + 1 ppm CEP |
Convergence time | < 10 s Cold start 27s - 37s Cold start takes more time | < 10 s Cold start 28s -29s |
VSupply | 2.7 V to 3.6 V | 3.3V DC +/-10% Consumes more power |
Interface | Driver needed. | Driver needed. |
Weatherproof? | −40 °C to +85 °C | −40 °C to +85 °C |
Model | Frequency Bands | Features | Accuracy | Cost (breakout board) |
|---|---|---|---|---|
PX1122R | L1, L2 | position | 1cm + 1ppm | $85 |
PX1125R | L1, L5 | position | 1cm + 1ppm | $50 |
PX1172R | L1, L2 | position | 1cm + 1ppm | $60 (bare) |
PX1172RH | L1, L2 | position, heading | 1cm + 1ppm | $150 |
PX1175RDP | L1, L2 | position, dead reackoning | 1cm + 1ppm | $70 (eval board) |
TLDR: PX1122R is good for us due to the following reasons:
Supports L1, L2 (we not going with L5 as only 17 satellites support it yet).
Cost effective
High accuracy
It is not as popular as F9P; but has seen success in the droning community.
Waiting for confirmation from @Anthony Luo that we only need position data from the GPS and not heading data too.
Recommendations
PX1122R
Outcome
For M8P | For F9P |
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Changelog
| Version | Date | Comment |
|---|---|---|
| Current Version (v. 7) | 2023-11-23 02:16 | Ayoung Eun |
| v. 6 | 2023-11-23 02:14 | Yashashwin Karthikeyan |
| v. 5 | 2023-11-23 01:25 | Ayoung Eun |
| v. 4 | 2023-11-16 00:18 | Yashashwin Karthikeyan |
| v. 3 | 2023-11-15 23:51 | Ayoung Eun |
| v. 2 | 2023-11-15 09:55 | Ayoung Eun |
| v. 1 | 2023-11-09 01:13 | Ayoung Eun |