Hi!
Having nothing to do in this days of self-isolation, I decided to make a spring service on my TSDZ2 bike that I assembled last year.
So I realized that there is about 2 mm play in my front sprocket, way too wobbly for my taste and with only 500 km under my wheels
Removing the front sprocket, I realized that it already started to eat into the plastic gear cover (exibit A):
I think I know where is the problem.
Initially, Tong Sheng was using straight cut "big gears", and those were probably fine (in that "woblines" parameter), but at some point, somebody decided to use helical gears, to reduce the noise - and here lies the problem.
According to the available data, this motor can produce somwhere around 100 Nm of torque, so I will use this number for calculation. Radius of the "big gear" is about 58 mm. To produce 100 Nm of torque, motor must provide 1724 N (it is like weight of 175 kg!). So far, so good.
Introducing helical gears, it also introduces axial force (Exibit B):
Based on the photo, it seems that the tooth angle is aboout 10 degrees (give or take), and that will produce about 17% of radial force (in our case, 293 N or about 30 kg weght). The pressure on the outer ring of the sprag clutch, since it's diameter is roughly 1/2 of the "big gear", would be doubled, about 586 N. Based on the tooth orientaion, this force is oriented inwards at the top where small gear is.
Disclaimer - I am not mechanical engineer, and I don't have any special knowledge about gears and bearings, this is just my humble opinion.
I believe that some good quality roller bearing may cope successfuly with that axial force, but sprag clutch is not a roller bearing, allthought it looks wery similar. It is designed to transfer the torque from the pedal, so when the pedal is pressed, small bits inside will lock in place and the whole assembly act as one solid piece. When motor is engaged (and axial force applied), pieces inside the clutch will orient in the loose position, and that must include at least some play, which got worse with time. So i think it is safe to say that wobblines is included in the design.
As a temporary solution (to avoid scratching the plastic cover), I put 5 washers between the gear and the chain sprocket.
I should probably replace the sprag clutch, but currently it is impossible to get one, and i don't know how long it will hold either.
It is a real shame, as this is otherwise so nice motor.
I would appreciate if somebody more experienced can share her/his oppinion on this.
Having nothing to do in this days of self-isolation, I decided to make a spring service on my TSDZ2 bike that I assembled last year.
So I realized that there is about 2 mm play in my front sprocket, way too wobbly for my taste and with only 500 km under my wheels
Removing the front sprocket, I realized that it already started to eat into the plastic gear cover (exibit A):
I think I know where is the problem.
Initially, Tong Sheng was using straight cut "big gears", and those were probably fine (in that "woblines" parameter), but at some point, somebody decided to use helical gears, to reduce the noise - and here lies the problem.
According to the available data, this motor can produce somwhere around 100 Nm of torque, so I will use this number for calculation. Radius of the "big gear" is about 58 mm. To produce 100 Nm of torque, motor must provide 1724 N (it is like weight of 175 kg!). So far, so good.
Introducing helical gears, it also introduces axial force (Exibit B):
Based on the photo, it seems that the tooth angle is aboout 10 degrees (give or take), and that will produce about 17% of radial force (in our case, 293 N or about 30 kg weght). The pressure on the outer ring of the sprag clutch, since it's diameter is roughly 1/2 of the "big gear", would be doubled, about 586 N. Based on the tooth orientaion, this force is oriented inwards at the top where small gear is.
Disclaimer - I am not mechanical engineer, and I don't have any special knowledge about gears and bearings, this is just my humble opinion.
I believe that some good quality roller bearing may cope successfuly with that axial force, but sprag clutch is not a roller bearing, allthought it looks wery similar. It is designed to transfer the torque from the pedal, so when the pedal is pressed, small bits inside will lock in place and the whole assembly act as one solid piece. When motor is engaged (and axial force applied), pieces inside the clutch will orient in the loose position, and that must include at least some play, which got worse with time. So i think it is safe to say that wobblines is included in the design.
As a temporary solution (to avoid scratching the plastic cover), I put 5 washers between the gear and the chain sprocket.
I should probably replace the sprag clutch, but currently it is impossible to get one, and i don't know how long it will hold either.
It is a real shame, as this is otherwise so nice motor.
I would appreciate if somebody more experienced can share her/his oppinion on this.
