If you crash enough that you are too frequently damaging your spool you can build a slipper spool out of a front diff. I think Losi was the first to do this with their XXXS.
A slipper spool functions the same as a spool under normal racing conditions but if you crash the out drives can slip to prevent damage
To do this you will need a front ball diff. If your car uses diff out put blades on the drive shafts you can use alloy diff out puts. If your drive shafts use steel pins you need to use steel diff outputs.
This is how to make a slipper spool:
1. Disassemble your ball diff and remove the diff balls. Clean the diff pulley with motor spray untill all the diff lube is gone. Clean the diff rings the same way.
2. Glue card stock (header cars, business card, note card,...) to one side of each diff ring with CA. Cut out the rings so you end up with diff rings faced on ove side with card stock.
3. Re-assemble the diff without the diff balls and with the paper side of the diff rings toward the diff pully.
4. Tighter and adjust your new slipper spool like a ball diff. On a Schumacher we tighten the diff screw until it stops then back it off ~1/4 turn.
The card stock takes up the space the diff balls took up so the width of the diff remains correct. The paper also makes it harder to slip.
As long as you don't hit anything its a spool and it will not move. However, it will move if you crash and allow the energy of the crash to disperse before you blades, drive shafts or suspension gets damaged.
Note that this works better on cars with stout M3 diff screws like Schumachers and Xrays. If you have a small diff screw it may snap. In that case run a normal spool and learn not to crash