An evolution of Solomon's K3 frame kit, this frame kit is designed for modular 3 to 3.5" heavier quads that are not only robust but also very convenient for replacing broken arms.

• Wheelbase : 148.6mm 
• Total thickness of arms and bottom plates : 5mm (2.5mm each)
• Thickness of top and side plates : 2mm
• Motor mount : φ9-12mm, M2 (2pcs. each)
• FC mount : 25.5x25.5mm, 20x20mm, M2
• VTX mount on Top Plate : 25.5x25.5mm, 20x20mm, M2
• Stack height : 15mm (enough to accept most AIO FC with a naked single PCB vtx)
• Camera width : 14mm
• Compatible with whoop style USB connector
• Built-in battery strap holder (can use up to 15mm width strap)
• Weight : Approx. 29g (Carbon only)
• Necessary Standoffs : 6 M2x15mm, 2 M2x14mm

How to assemble :
The use of metal locknuts is strongly recommended. Each arm must be securely locked to prevent wobbling. In the picture below, the screw holes painted red need to be locked by metal locknuts, and the screw holes painted yellow are auxiliary ones to secure them if you are concerned about using heavy batteries. The screw holes painted blue are, of course, for the flight controller.

Motor Mixer :
This frame has a wide-X shape, and the distance between the left and right motors is larger than the distance between the front and rear motors. As far as FPV flights are concerned, the flight characteristics of the wide-x frame can be quickly accustomed after a few flights and do not cause any inconvenience at all. However, in order to enjoy line-of-sight flights as well, I think it is necessary to set the motor mixer appropriately. The motor-to-motor distance of this frame is 115.5mm and 93.5mm; their ratio is 93.5/115.5 = 0.810. Therefore, the CLI command of Betaflight Configurator to properly set the motor mixer is as follows:

mixer custom
mmix reset
mmix 0 1 -1 0.810 -1
mmix 1 1 -1 -0.810 1
mmix 2 1 1 0.810 1
mmix 3 1 1 -0.810 -1 
save

Dimensions :

Lower Layer of Arms and Bottom Plates :

Upper Layer of Arms and Bottom Plates :