[EricVanWyk]

A 40 Amp breaker doesn't magically break at exactly 40 Amps; the trip time is an imperfect function of its internal heating, which is a function of current. When the metal strips inside reach a certain temperature, they bend and push away from each other.

CIMs can draw upwards of ~120Amps if you stall them. At that draw, the breakers should pop within a few seconds. But you aren't stalling them, you are simply asking a lot of them. It is very possible you are drawing 60-80 amps many times a match.

The first time you do this, your breakers won't trip because they are cold. Each time after that, you run an increasing risk of popping as they heat up.

Adding two more CIMs will definitely help the situation. In the mean time, you can reduce the load on your motors by reducing any friction you may have in the transmission.