While I was having a blast riding my e-bike, I was also dropping my chain at least once on every ride. After my 1st hundred miles of riding this problem became very annoying. The chain drop was caused by the chainline. Ideally, the front chain ring and the rear sprockets should be parallel to the centerline of the bike and angled as little as possible, see illustration below. But, when the chainline is mismatched there is a sideward stress on the chain that causes the chain to drop off the front chainring.
It seems a bit short sighted for Bafang to ignore this design issue on a bicycle conversion kit. They must be aware of the problem. A google search on “Bafang Chainline” will illustrate countless examples of the problem as well as offer numerous solutions to this issue. Simple design changes like placing the Bafang Motor Controller on the non-drive side of the motor or adding chainring spaces to better position the chainring would have greatly reduced the chainline angle.
My solution didn’t address the chainline but it did eliminate the chain drops. Since I already had a front derailleur, I simply reinstalled it and adjusted the limiter screws to perfectly align the front derailleur to act as a chain guard to keep the chain from falling off the chainring. While I do get some chain rub on the front derailleur in my lowest gears, the problem is solved at no additional cost.
Ken Whittaker