Table 2.

Summary of phenotyping robots categorized by drive mechanism. 4WD4WS: four-wheel driving and four-wheel steering; 2WD2WS: two-wheel driving and two-wheel steering.

Robot	Phenotyping sensor	Perception sensor	Crop	Advantages	Disadvantages	Applications
Wheeled robot (skid steering)
VinBot [28]	RGB-D camera 2D LiDAR	RTK-GNSSIMU	Grape	Simple mechanical structure Simple motion control Low cost	Low power efficiency in turning High wear and tear of the tires Can cause damage to the soil	Yield estimation [47]
Shrimp [25]	3D LiDAR RGB camera Hyperspectral camera	RTK-GNSSIMU	Horticultural crop			Mango fruit detection [25] Almond mapping of flower, fruits, and yield [48] Almond fruit detection [49]
Robotanist [26]	Stereo camera RGB camera	RTK-GNSSIMU2D LiDAR Stereo camera	Sorghum			Corn stalk count and width estimation [50]
Vinobot [24]	Trinocular camera	GNSS2D LiDAR	Maize Sorghum			Simulation of Vinobot [51]
TerraSentia [27]	Multispectral camera2D LiDAR Hyperspectral camera RGB camera RGB-D camera	GNSS Gyroscope	Maize			Corn stem width estimation [52] Under canopy navigation [53]
MARIA [29]	2D LiDAR RGB-D camera	RTK-GNSSIMU	Not specified			Simulation of an agricultural robot [54]
[55]	RGB-D camera	RTK-GNSS2D LiDAR	Maize			Corn stalk diameter estimation [55]
Wheeled robot (differential drive)
RobHortic [30]	Thermal camera Multispectral camera RGB camera NIR camera Hyperspectral camera	RTK-GNSS	Horticultural crop	Simple mechanical structure Simple motion control Low cost	Less precise in steering control	Carrot disease detection [30]
Wheeled robot (2WD2WS and Ackerman steering)
AgBotII [31]	RGB camera	RTK‐GNSS	Row crop	Precise steering control	Need coordination between drive wheel and steering wheel	Weed detection [56]
Phenobot 1.0 [32]	Stereo camera	RTK‐GNSS	Sorghum			Sorghum plant height and stalk diameter estimation [32] Sorghum plant architecture [57]
AgriRover-01 [33]	3D LiDAR	RTK‐GNSS	Corn			Plant height and row spacing estimation [58]
DairyBioBot [34]	2D LiDAR NDVI sensor	RTK‐GNSS	Ryegrass			Ryegrass biomass estimation [34]
Wheeled robot (articulated steering)
Phenobot 3.0 [2, 35]	Stereo camera	RTK-GNSS	Sorghum	Good mobility for rough terrain Precise steering control	Increased complexity in mechanical structure
Wheeled robot (4WD4WS)
Thorvald II [36]	Application dependent	GPSIMU2D LiDAR	Row crop Horticulture crop	High maneuverability Good terrain adaptation	Complex mechanical structure Complex motion control High cost	Development of a strawberry harvesting robot [59] Development of row-following algorithm in polytunnels [60]
Ladybird [37]	RGB camera2D LiDAR Hyperspectral camera Stereo camera Thermal camera	2D LiDAR RTK-GNSSIMU	Row crop			Weed detection [61] Dataset collection [62]
Phenomobile V1 [38]	2D LiDAR RGB camera Multispectral camera	RTK-GNSS	Row crop Wheat Mixed crop			Estimation of plant height from LiDAR measurement [38] Estimation of wheat green area index from LiDAR measurement [63]
AgRover [64]	Not specified	RTK-GNSS	Row crop
Flex-Ro [39]	RGB camera Ultrasonic sensor Infrared thermometer Spectrometer	GNSS Obstacle detector	Row crop
MARS X [40]	Application dependent	RTK-GNSS	Row crop
Tracked (differential drive)
Armadillo Scout [41]	Application dependent	GNSS2D LiDAR	Not specified	Good mobility for rough terrain Low ground pressure	Complex mechanical structure Low power efficiency in turning Can damage the soil
PHENObot [42]	RGB camera	RTK-GNSS	Grape			Grape bunch and berry detection [66]
[65]	RGB camera	RTK-GNSS	Soybean
[43]	RGB camera
TERRA-MEPP [44]	Stereo camera Depth camera RGB camera	RTK-GNSS Wheel encoder Gyroscope	Sorghum
Phenomobile V2 [45]	2D LiDAR RGB camera Multispectral camera	RTK-GNSSIMU	Wheat Cotton Sunflower Mixed crop
Wheel-legged (4WD4WS)
BoniRob [67]	Application dependent	RTK-GNSS Inertial sensor3D LiDAR	Row crop	High maneuverability Good terrain adaptation Physical dimension can be changed	Complex mechanical structure Complex motion control High cost	Soil compaction and moisture measurement [68] Weed image dataset collection [69] Image dataset collection [70] Ground and aerial robot collaboration [71]