Gotcha.

This is a riding mower, correct?

Have you ever watched Mythbusters? They are commonly tasked with rigging up a car or truck with model-airplane-style remote controls. Whenever they do it, it looks like they need to do it in a very heavy-duty fashion to make it work reliably. For example, the actuators look like they have to use either hydraulics or linear drives, and they've always got the top-of-the-line high-power radio controllers. Make sure that whatever you use is up to the task and isn't too weak to get the job done.