This OpenSCAD script started out as a design meant for just the T4 series of multirotors, but I decided to add more parameters to accommodate different motor-mount and arm angles. I considered creating a customizer for it, but decided against due to complexity.

I've been making mine with 30% infill and no support, and they seem to be strong and light.

I've tried to write useful comments in the code. I should probably add a diagram graphically showing what all the parameters mean; I hope to get to that later.

Ignoring, for the moment, the initial rotate([0,0,45]) directive, you should imagine the multirotors's arm extending out along the X axis. Then ang_offset is the angle that the screw-hole slots make with respect to the X axis, and arm_ang_1 through arm_ang_3 are the angles that the three arms make with respect to the X axis. Keep in mind that positive angles correspond to counter- (or anti-) clockwise rotation.

The vent slots are meant to correspond to the ones in the T4 arms, and in any event can be suppressed by setting do_vent_holes to 0.

I put that rotate([0,0,45]) directive there just to orient the print so it fits a little more cleanly on a square build bed, but feel free to adjust/remove it.