Hi all
I have built a twin motor eMTB project using a Bafang G020 front motor and a Bosch Gen 2 mid motor, each motor is controlled by its own CA V3 & PhaseRunner combination. The CAs both share the same throttle, brake, 1 wire PAS RPM sensor & connection to the original, internal Bosch torque sensor. The Bosch is currently fed power from the original Bosch 36v battery, whilst the Bafang is fed from an independent 52v battery; earths are linked at the CA inputs, but not at the main battery earth leads.
On first testing I had 3 major problems:
1) On pulling away using pedal assist only, both motors would surge to near full power before gradually settling down after 2 or 3 seconds, this happened regardless of which level of assist was selected, even very modest ones.
2) When I stopped pedalling, both motors continued to run, but would gradually ramp down over several seconds.
3) When I shut the throttle, both motors would surge to a high power level before gradually ramping down over several seconds.
I eventually managed to bring No 1 under control by reducing PAS ramp up to 2v per second and increasing WGain to a setting well in excess of the “recommended range” of 8-25 @ 90.
After much more testing I worked out that issues 2 & 3 were both linked to running of the Bosch motor, as everything worked fine when only the front motor was running. The Bosch motor phase cables, plus 5v, earth, speed, PAS, torque & temperature sensor all run in a Grin supplied 10 core cable, the signal cables being screened (the whole cable is fed through the down-tube), at both ends the signal cables split off to go to their respective connections, however, at the motor end, the torque sensor signal wires continue run parallel to the phase cables. After a bit of research, mainly on Endless Sphere, I decided that the problem was likely to be interference related, so I made another, temporary torque sensor loom that I hung away from the phase wires & frame (apart from 1 zip tie to the outside of the down-tube, to stop it snagging on the front wheel; this made no difference!
After yet more testing, I realised that the problem was that I had mounted the magnet ring for the PAS RPM sensor to the “chain-ring” guard (as this was the easiest way to do it), so once the Bosch motor was running, it became self-maintaining, this despite there not actually being any torque applied, in fact torque goes slightly negative when the pedals are stationary & the motor running.
Next I designed & printed a new magnet mount, so that the magnets only rotate when the pedals are actually turning & eureka, everything now works fine, or so I thought.........
The main reason that I wanted the Bosch system to have throttle functionality is that I only have one arm and do some reasonably extreme off-roading. If the going gets sufficiently tough & I have to get off, it’s very difficult for me to push the bike, the previous addition of the throttle controllable front motor helped quite a lot, but on steep uphills it couldn’t get enough traction.
Anyway, I was testing throttle controlled “pushing” of the bike on a steep, garage access road & it worked great, until I got to the top & released the throttle; the bike took off great pace, tearing off the Velcro strap that fastens my false arm to the handlebars before I managed to grab the brake which shut everything down. What caused this is that, despite there being a freewheel in the Bosch gearbox, so that the motor does not force the pedals to turn with it, when your feet aren’t on the pedals, there is enough friction to turn the pedals and, when the throttle is closed, the CAs seem to think that they should apply a bucket load of power, again despite there being no torque applied. My question is, does anyone know how the CAs are programmed to function, as in, should they behave in this way or do I still have an interference problem?
I actually started writing this in order to send the question to Grin, which I will do, but I have been meaning to get round to writing a build thread for some time, but have been too busy actually building the bike, so I thought that now is as good a time as any. I will upload a load more info & photos in due course, plus I have a few more niggles to ask for help with when I get chance.
I have built a twin motor eMTB project using a Bafang G020 front motor and a Bosch Gen 2 mid motor, each motor is controlled by its own CA V3 & PhaseRunner combination. The CAs both share the same throttle, brake, 1 wire PAS RPM sensor & connection to the original, internal Bosch torque sensor. The Bosch is currently fed power from the original Bosch 36v battery, whilst the Bafang is fed from an independent 52v battery; earths are linked at the CA inputs, but not at the main battery earth leads.
On first testing I had 3 major problems:
1) On pulling away using pedal assist only, both motors would surge to near full power before gradually settling down after 2 or 3 seconds, this happened regardless of which level of assist was selected, even very modest ones.
2) When I stopped pedalling, both motors continued to run, but would gradually ramp down over several seconds.
3) When I shut the throttle, both motors would surge to a high power level before gradually ramping down over several seconds.
I eventually managed to bring No 1 under control by reducing PAS ramp up to 2v per second and increasing WGain to a setting well in excess of the “recommended range” of 8-25 @ 90.
After much more testing I worked out that issues 2 & 3 were both linked to running of the Bosch motor, as everything worked fine when only the front motor was running. The Bosch motor phase cables, plus 5v, earth, speed, PAS, torque & temperature sensor all run in a Grin supplied 10 core cable, the signal cables being screened (the whole cable is fed through the down-tube), at both ends the signal cables split off to go to their respective connections, however, at the motor end, the torque sensor signal wires continue run parallel to the phase cables. After a bit of research, mainly on Endless Sphere, I decided that the problem was likely to be interference related, so I made another, temporary torque sensor loom that I hung away from the phase wires & frame (apart from 1 zip tie to the outside of the down-tube, to stop it snagging on the front wheel; this made no difference!
After yet more testing, I realised that the problem was that I had mounted the magnet ring for the PAS RPM sensor to the “chain-ring” guard (as this was the easiest way to do it), so once the Bosch motor was running, it became self-maintaining, this despite there not actually being any torque applied, in fact torque goes slightly negative when the pedals are stationary & the motor running.
Next I designed & printed a new magnet mount, so that the magnets only rotate when the pedals are actually turning & eureka, everything now works fine, or so I thought.........
The main reason that I wanted the Bosch system to have throttle functionality is that I only have one arm and do some reasonably extreme off-roading. If the going gets sufficiently tough & I have to get off, it’s very difficult for me to push the bike, the previous addition of the throttle controllable front motor helped quite a lot, but on steep uphills it couldn’t get enough traction.
Anyway, I was testing throttle controlled “pushing” of the bike on a steep, garage access road & it worked great, until I got to the top & released the throttle; the bike took off great pace, tearing off the Velcro strap that fastens my false arm to the handlebars before I managed to grab the brake which shut everything down. What caused this is that, despite there being a freewheel in the Bosch gearbox, so that the motor does not force the pedals to turn with it, when your feet aren’t on the pedals, there is enough friction to turn the pedals and, when the throttle is closed, the CAs seem to think that they should apply a bucket load of power, again despite there being no torque applied. My question is, does anyone know how the CAs are programmed to function, as in, should they behave in this way or do I still have an interference problem?
I actually started writing this in order to send the question to Grin, which I will do, but I have been meaning to get round to writing a build thread for some time, but have been too busy actually building the bike, so I thought that now is as good a time as any. I will upload a load more info & photos in due course, plus I have a few more niggles to ask for help with when I get chance.