Wild Thing Adaptation

Hello everyone! I am working on adapting Fisher-Price Power Wheels® Wild Thing. I read the blog of Reverse Engineered Wild Thing, and want to do the similar modification that controls the wild thing with mechanical switch running in a lower speed.

I have the Arduino connect to the low pass filters and an operational amplifier. The Arduino controls the voltage output on green and black wire which means velocity and on-off signal. However, with a same voltage output, the power wheel behaves differently, please see the video: Video

Just want to ask if anyone runs into a similar situation or knows how to deal with it?