It is not easy to switch from sarong to bed as you have already introduce yaolan to your baby. It takes some time to train your baby to sleep on the bed again. My baby also got this problem too. I introduced yaolan to him after 1 month old because whenever he slept on the bed, he got shocked and scared when there is a 'bang' sound or loud noise. Till now going to 1 year old, he still sleep in yaolan(with motor) to swing him whenever he sleep. However, i know that it is not very good for baby healthy.
As you mentioned also, whenever the motor stopped, he wake up and cry.