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DIY Fix for BBS02/BBSHD Pedal/Throttle Issue

Rassy said:
@opperpanter, thanks for the update concerning that the current stock from EM3EV still has the throttle issue. I would not hesitate to purchase one if I was in the market, but would plan to do the hardware fix. The one I fixed is in regular use and was worked properly for over two years now.

Yeah, it seems doable the mod. It's just that I can remember that the wires are very thin from when I was making my own programming cable.
Also it seems like the throttle just works in all PAS levels as long as you don't move your legs/pedals?
Yes, as long as you stop turning the pedals the throttle works correctly.

However, I represent the mild exercise and recreation style of riders, normally cruising along on paths at about 10 MPH in a very low PAS setting and just grab a little throttle when encountering a short hill or crossing a road. In these cases it is not natural to stop pedaling just to get a little extra power for a few seconds.

I also read where the off road riders (that often don't even care about PAS) like to pedal and use a responsive throttle in very technical situations.

In other words, the only ones that don't mind Bafangs throttle problem either never pedal and/or always ride at Wide Open Throttle.

One poster suggested obtaining a pair of the PAS connectors and making a small harness that can just be plugged into the existing PAS connectors so no cutting into the tiny PAS wires inside the controller cavity would be needed and the only wire that would need to be spliced into would be the throttle sense wire. I have also considered that one could more easily splice into the throttle sense wire outside the controller cavity where you would have more room to work and hence less chance of damaging other wires, and even making it easier to fix any unintended damage. Then that single small wire could be passed into the controller cavity through a very small hole you would drill through the rubber where the other wires enter the controller cavity.
I recently bought a bbshd to add to a new bike I am building and was a bit disappointed when I couldn't get the throttle and pas to work together like my old bbs01. So I came across this thread, I was a bit reluctant to dig into a new controller so I cut into the cable up near the throttle. Soldered into the blue throttle wire and black earth and joined them to the transistor. Then ran a thin wire down to the controller, I passed it between the rubber gasket and rubber block that the other wires pass through. I soldered that wire to a thicker single core copper wire and pushed it into the pas plug next to the grey wire, works great now. Thanks to Richard and the others for this thread.
Nice job mayon, glad you were able to fix your BBSHD. Your fix is pretty close to what I would do if I ever need to fix another BBS02 in the future. The nice part about your fix, which is similar to what I proposed in my post just ahead of yours is that it keeps you from having to do any real tight work within the controller cavity and also keeps you from having to mess around in the potting material. Probably would not void your warrantee since no modification was done to the controller or any of the wiring attached to the controller.

Thanks for posting.
Just been notified by em3ev they don't have any pre-2016 controllers at all, only BBS02B. So I may have to stock up if I want to keep riding my BBS02A motors.
Just done the mod to stop the snatchy throttle/PAS thing. Many thanks to Fetcher, Rassy and all others for your input.
I did the external version the same way as Mayon did in the above entry May 5th. Thanks Mayon.
I used the same components as Fetcher 2N5308 transistor and 100K 1/4W resistor and it works perfectly at higher speeds.
However, I still have the same snatchy throttle thing happening at low speed, low throttle position and low assist level......its not noticeable at higher throttle, assist levels or speed. Throttle start voltage is 1.1V.
I live in a mountainous area and love to blast along the off road tracks but I also ride a lot of slow undulating tight trails where frequent dabs of throttle are needed at low speed when in PAS.
Can anybody tell me if I change the resistor to a lower value like 50K will my throttle take control before the PAS and give me smooth throttle control at low speed?
Brad, nice that worked out for you. The problem at low speed that you mentioned is also present in the older BBS02s that worked "properly". I think what happens is right at the point where the throttle takes over for the PAS system there is a very small dead space where the throttle signal isn't strong enough yet but the PAS signal has been disabled. Most of the time this issue does not present itself because the normal use of the throttle to override the PAS system is because you want some more power to get up a hill or cross a road, etc. and you don't just sit at that transition point. If you turn PAS off (i.e., PAS 0) you should not have that issue.

If you are bothered by this issue you may be able to lessen the impact or even eliminate it by making changes like you suggested, such as changing the throttle range or the resisters used in the "fix", etc.

In my case I only noticed the issue because I was testing for the original problem and was modulating the throttle at that point on purpose, which is how I discovered this issue was also present in my older "good" controllers.

I'm not very technical, so if anyone can address this issue better, please do so.
Brad777 said:
Can anybody tell me if I change the resistor to a lower value like 50K will my throttle take control before the PAS and give me smooth throttle control at low speed?

Changing the resistor won't change the point where the throttle takes over by much. Changing the throttle low setting in the programming might do something closer to what you want but I have not tried that.

There are some alternate circuit designs that can kick in at a lower voltage.
Thanks Rassy and thanks Fetcher for your feedback.
Thinking back to my first BBSHD in 2016 I remember now that when the throttle takes over there was a small dead band where the throttle signal's not strong enough and this does feel the same but maybe a little more obvious on this setup.
I might try raising the low throttle voltage again to see if that helps but from what you both say I may just live with it as it is.
I'm really pleased with the result regardless of the low speed issue and its so much easier ride now.
Happy days!
Fetcher are the alternate circuit designs that kick in at a lower voltage worth trying? Maybe too much trouble?
Kind regards to you both.
Keep in mind that if you slowly advance the throttle, at some point the transistor kicks in and disables PAS. Right at this point, the throttle setting may be lower than what is needed to make the motor spin, so power will drop out until you advance the throttle a little more. You could try raising or lowering the low throttle voltage setting in software and see what it does. Actually lowering it might help more.

You could also try changing the resistor in the circuit, but I don't think it will make much difference. You could go as low as 10k on the resistor. You could place a 10k across the existing 100k just for a test.
I changed the start voltage and I don't think it made much difference but at 0.9V I got error-5 and at 1.3V the motor wouldn't stop till I pulled the brake and the brake sensor stopped it......I've reset it to 1.1V
I agree after thorough testing today over 29 miles that the point the transistor kicks in the throttle setting is lower than that needed to make the motor spin and power drops out until the throttle position is increased.
I don't think i'll try to change this anymore as it only affects the lowest throttle position. I'll just enjoy the fact I can now hit the throttle anytime without that horrible jerky thing happening.
Thanks again both of you.
Yes, that's the way it's going to work. If you slowly advance the throttle when it's motoring in PAS, there will be a dead spot until you bring the throttle up enough to make the motor spin. The real fix would be a firmware change but that's not an option at this point.
Thanks fechter and all :)

I've applied transistor the fix to my brand new BBS HD and the throttle is working really well (as good as a pre 2016 BBS02 I have built)

I didn't do anything special and I would say to others reading, the potting is nothing like as bad as i thought.....just get in there.

Perhaps there are different types of potting but I had spent too much time reading and not enough time doing. You can easily easily remove it, cut it, separate it or just generally pick at it with anything blunt. Use all the good photos here to guide you as only a little needs to come off.

I was able to pop the board out of the housing by 'breaking the seal' so to speak after taking the potting off around the edges and prying a little between outer casing and the transistor heat sink. Once the board wiggles even a tiny bit you are there. I had it out in just a minute or so.

Mine had little thermal paste and a lot of the potting had bled into the gap between heat sink and housing. This makes we wonder how much cooling they need? I doubt the potting is a great thermal bridging material.

I modified on the side where the wires are attached to the PCB, connected the throttle wire direct to PCB and by popping the pins out of the PAS connector I was able to splice with heat shrink over them.









Also swapped the shunts and so far so good at 40a :p

On the bikes I have with BBS02B controllers, I noticed the funky PAS/throttle interaction as described on this thread. Maybe it's just me (or my bikes) but I reduced the Keep Current % on the PAS page from my normal 100% to MAX 90% and now the PAS and throttle work together great.
fechter said:
The circuit diagram looks like this:
Darlington Circuit.jpg

I used the above circuit with an MPSA13 and a 100k resistor, but due to the mechanical obstructions (chains, tensioners etc.) and wiring already fitted, I decided to take a slightly different tack. I have a Grintech 24P external PAS sensor on the freewheel jackshaft and so made a 'T' adaptor loom to connect the 2 wires coming from the darlington circuit and the transistor's Base which is tapped into the blue thumb throttle wire in the cockpit. This way I felt I could obviate disturbing everything in the nose of the vehicle.

My result after the mod was 'no change'. now the questions (before I resort to doing it the way I perhaps at first should have).
Grintech show the BBS controller colours meaning: Grey=RPM, White=Direction, Black=GND, Red=+5V
Are those the correct functions for the colour codes?
I don't know anything about the Grintech PAS unit, but on the BBSHD, the grey and white wires are both pedal RPM sensors that are in quadrature so the MCU knows the pedal direction.
fechter said:
I don't know anything about the Grintech PAS unit, but on the BBSHD, the grey and white wires are both pedal RPM sensors that are in quadrature so the MCU knows the pedal direction.

All sorted. I discovered a discrepancy between the pin out diagrams of the PAS JST connectors for the BBS02 diagram and the Grintech external PAS. Prior to the fix, my PAS was either ON or OFF and that was with the RPM and DIR wires reversed (using the connector pin positions rather than eyeballing the BBS PAS connector which had the white and grey (gray) wires reversed).
Finally I resorted to cracking the case open enough to add my little circuit (on a scrap of veroboard and using a 68K resistor).

Wow! finally a smooth operating motor which has throttle priority over PAS. Well done Fechter for your fix which has made the use of my velomobile such a joy. If we didn't suffer the tyranny of distance I'd shout you a well deserved ice-cold amber beverage.
Glad that worked out. I still wonder why Bafang made it that way. My best guess is to comply with some silly regulation somewhere but it really doesn't make any sense to me. Luckily the hardware hack is fairly easy.

After pandemic madness, heat waves, earthquakes and massive fires, I'm ready for some of that amber beverage.
+1 to the firmware update from Tomblarom in the thread linked above. Completely solved the problem with my throttle!
Hi everybody, I've read through this and similar threads, and I'm a little scared by all the cutting and transistors and things. I'm about to buy a new BBS02 to replace my hub drive, and I'd like to keep the same characteristics, ie, pedal when I like, throttle when I like, and control how they interact myself, especially on lowish speed trail work, which is what I'm building it for. So I'm worried about the jerky throttle on/off problem when riding. I never want to use Pedal Assist, ever. Am I right in thinking even in PAS 0 I'll still get the throttle problem, and is it possible to disable PAS without going inside the cases/controller please, and will that solve my problem? Thanks in advance. :thumb:
It's pretty easy to open the side cover and simply unplug the PAS sensor. This disables the PAS completely and gives normal throttle response. I rode this way for about a year. If you want PAS later, you can reconnect the plug.

BBS02 PAS.jpg
Just that black plug, just disconnect it and job done? I reckon even I could manage that (hopefully). Many thanks, I'll get my motor ordered then.... Cheers :)
That's it. Just unplug it.
There is usually a little blob of silicone holding the plug but you can just pull hard and it will tear or you can slice it with a blade first.

If you're sure you won't ever want it again, you can also just snip the grey wire and leave the plug in.