You could try changing the sketch to control the motor without using the pot or switch. It could start slow in the forward direction, gradually get faster, slow down and then go into reverse, repeating the pattern.
OUT OF STOCK NOTIFICATION
You have been successfully subscribed to the Notification List for this product and will therefore receive an e-mail from us when it is back in stock!
For security reasons, an e-mail has been sent to you acknowledging your subscription. Please remember that this subscription will not result in you receiving any e-mail from us about anything other than the restocking of this item.
If, for any reason, you would like to unsubscribe from the Notification List for this product you will find details of how to do so in the e-mail that has just been sent to you!