I’ve found that by mounting my motors facing outward, and positioning the chain guide roller screws loose enough to allow the nylon spacer to spin, I have NO need for the bungees or counterweights, never had a skipped chain, plenty of adhesion, all good.
My current design actually places the motor below the unistrut, unlike the photo above. This lets the back of the motor mount bracket hold flush and true against the strut body and makes for an exceptionally stiff connection.
hope this helps,