You might need to tap the axle holes... better safe than sorry.
Or, you could warm / soften the plastic with a hand torch and thread the hole with the screw.
Make sure that the wheel on the front doesn't bind; you might need to sand around the axle a bit.
The mounting hole in the wheel is purposefully small to allow for the widest possible screw size. Widen the hole with a drill bit that is slightly larger than the threads of your screw.
Insert your M3 hex nut...
Insert your M3 hex nut...
And screw the sonar mount to the chassis.
Pilot holes are needed to mount the servo to the chassis. A 1/16 inch bit will do nicely.
Take it slow... if you hear any kind of cracking you might want to warm / soften the plastic a bit before proceeding.
Let's get to work on the rear wheels.
Servo horns are typically white or black... grab one, and trim it to fit.
I tried using model cement this time... which works, but it will take an hour or so before the wheels are solid enough for final assembly.
5 minute epoxy might be a better alternative.
5 minute epoxy might be a better alternative.
Repeat these steps for the other wheel.
