6 cells just flat out suck. alkalines suck even worse. Thats your problem right there.

a 4 cell with a good set of rechargeables would be better. Lithium would be even better yet. That motor probably requires more battery than the alkalines can feed it.

Also your car does work? pin 3 from the left on the first stack is touching that other metal.. im surpised that doesnt cause a problem...