I've ordered 2 Kazi trains on aliexpress. Seemed like a nice set with some tracks for my kids. As seen below it's a set where the power box is a separate part and it runs a motor that connects to the wheels by a bunch of gears. Problem I have is that the trains are struggling to run. Yellow one more than green, maybe due to weight. Anyone had a similar problem and knows how to improve the set? I'm wondering if switching to the undercarriage motor would work on these sets. The larger ones seem to have a different kind of motor that has no gears to get it moving and provides power directly to the wheels but not sure if that one would fit. Considered applying some grease but not sure how much that can help in this case without making everything sticky.