Good thing about that circuit is that you can attach the output of your big motor to the servo arm for feedback. Acts like a giant servo and can be used with the transmitter mod that some antweights use for their flippers (47k ish resistor shorted across the top half of the throttle channel via button)

You'll want to change the connection order on the relays so their normal state is off and not shorting the battery by attaching both Normally Closed pins to battery +, both Normally Open pins to battery - (or the other way around, doesn't really matter) and the motor across the Common pins.