According to the story you described, I think it should be this episode: the birth of the new friendship car, the second WGP episode of the four-wheel drive brothers.
This is the online viewing address of episode 35:/v _ show/v _ show/ID _ xmtcwmtm2ody0.html.
When the video was played to 13 minutes and 30 seconds, Xiao Hao sat on the floor and there was a big crack in that position. He accidentally fell from that big hole. Coincidentally, Xiao Hao found the ZMC chassis at this time, which is really interesting! God helped Xiao a lot! How lucky!
I hope my answer can help you!