Conventionally with the sort of hand-built commercial drones that sell for five-figure sums, the means of mounting the motor is to design a plate or outline that can be cut from carbon-fibre sheet using a laser-cutter... which is expensive.
I bolt them direct to inch-square tubular alloy as I have done generally for each of the prototypes that we have flown (including the last in December of 2021).
At the scale considered for our current effort, 20mm square alloy is a better choice, but then at the thickness it comes from the supplier (2mm) the tube-connectors that I use do not fit inside. Our world rotates round stock dimensions of one inch or 25mm.
Accordingly looking at that section superimposed on T-motor's technical drawings, we can see that the four bolt-holes for fixing U-7 motors range around a 30mm diameter circle... which means that the distance between each is rather less. In fact, at around an inch (as seen in the figure on the left) it does not at all suit direct attachment.
What I've done in the past is to rotate it through forty-five degrees and then fix the motor with two bolts directly through the spar, with the outliers pinned to angle-alloy fixed along its sides. In this case as you can see, it is a close call... whereas with U-11 motors which I used previously, the bolt-holes were arrayed around a 40mm circle.
Nonetheless it should be do-able. In fact we discovered that airframes flew perfectly safely with just two bolts ~ those within the confines of the spar ~ in use.
Experts in the field had endless worries over this with torsion and resonance issues, none of which materialised. Whilst people with giant drones are generally patronised, on one hand I flew jet airliners that had been brought to grief by such issues, and on the other I'm aware that the Wright Brothers were also dismissed as cranks.
So as Andy Warhol once said, If people hate what you are doing then keep on doing it.
