Hi, my m548 needs something better than the current gearboxes. Anyone triedbor know if it's possible to use modified servos to replace motors/gearboxes?

Its possible to use a servo motor for a drive motor. But it must be modified for full rotation. Also I find they are very noisy - they are really only intended for short movements. Another downside they are usually geared very low - so they may be too slow for your vehicle. But a metal gear version should have plenty of torque. Another downside of a servo is the output shaft spline - its difficult (not impossible) to adapt something to fit that spline, but you don't have a lot of shaft to work with. One more consideration would be cost. Servo's esp metal geared ones aren't cheap - generally $25-30 USD. You can usually find a geared 12V motor for less. I also find they sometimes need a lot of trim to stop moving. I use one for a turret rotation motor and it requires +22 clicks of trim to stop moving. One nice thing about a servo as a motor is they dont' need much voltage- they can usually be powered directly from the radio Receiver without an ESC. For small tiny vehicles a servo is a good choice for drive as they come in tiny sizes. But for larger heavier models a geared DC motor is the way to go for tracks.

If it was me I would not use a servo as a drive motor on a tracked vehicle. But I'm sure someone will chime in who loves them!
Best regards,
Bob

What kind of gearboxes are in there currently? I know there are some on this board that have replaced motors with better ones to get better performance and fairly cheaply.

Agree with all. I've modified a servo to use as a winch and it's very difficult to make it stop moving. The potenciometer it's very sensible

Metal HengLong but modified to 55t 540s. The gears are crap but I can't spend much in better ones. The tank weighs 4.8kg