Virgin post to the group

[vk4bxi]

The subject says it all.
I am about to buy a BBS 02 750 watt drive for my 26"/1.95" wheel bike. Its got currently a 24/36/42 front gear and a 14....34 rear.
I am an electrical engineer 65+ and definitely in need of assistance to get out of the "hole" of an estate that I live in ( a 30 metre 20% grade climb out) into the very hilly area that surrounds it.
The specs for the BBS 01 of 30Nm cont and 80Nm peak is not good enough to get my carcase (110kgs all up ) up and out of the "hole". I estimate that I will need about 80Nm to do that if use the 36 of 36/42 front gears that I want to retain with an adapter ring.
I can find power calculators for hub drives is there one for mid drives to check this ?
I can't find out from the bafang site or in the posts here just what the BBS 02 can do. Although one vendor claims the BBS 02 750 watt can do 120Nm peak. Please does anyone know where I can find the cont and peak torque ratings for the BBS 02 750 watt motor/drive ?
I would prefer not to have to go to the BBSD if possible, although even that one is only posted at 160Nm peak with no continuous rating available.

Also I want to add in gear change sensing. Does the latest BBS 02 750 watt have a proper input for that like the BBSHD does or will I have to do cutting of leads etc.

Thanks for being patent and reading this.

Regards Bob

 

[nutnspecial]

Greetings sir! !

I don't know if the bb02 can do the shift sensing.

I can't provide or even particularly point to numbers for any of the bafangs.

I can only say greetings and that a human can put out 100 - 200 watts. So if the hill is able to be pedalled at all, even a 250w will make alot of difference. With a bb02 (750w - nearly a hp) you shouldn't have a problem maxing out the bicycle drivetrain capabilities. I'm thinking that and the 24 chainring to 34 cog will certainly be enough.

If you want to play with actual numbers and there are none posted, perhaps a similar motor under similar power can be considered, and then add in your max bike ratio. There is a simulator (perhaps on ebikes.ca ?) with some motors preloaded on it. Welcome!

 

[vk4bxi]

Hi and thanks for the welcome, on a very good day (only one of those so far) I have made it to the top with the 24:34 gears. The "old" back gear set with a largest cog of 28 was impossible for me even with standing on the pedals, and as I said I did it with the 34 gear back gear only once. The BBS-02 is going to limit me to a maximum of 2 front gears so at present I will reuse the 42:36 front gears that I have on the current setup. (I do have a workshop with metal working lathes and stuff to make bushes and spacers) So I need to know what the maximum torque out of the motor is. The bafang website lists only the 750 and 1000 watt motor sizes but says that they both have the same max torque rating ? !! ? of 160Nm, this seems odd when some postings state that the BBSHD has a larger core width than the 750 watt core. So go figure ! The available info does not add up. Those who do "know" please stand up and comment.

 

[vk4bxi]

Ok it looks like I'm answering some of my own questions.
Base data comes from the original BBS 01 manual, there if one uses the Torque X Speed = Power then the data there works for me.

I.E. 250 watts = 80 RPM / 60 X 2 X Pi X 30 Nm so the 250 Watts is shaft output mechanical power and not the amps and volts applied to the motor which is 9 X 36 volts ~ 324 Watts or the drive and motor combination is 250/324 = ~ 77% eff.

So if I do the same with the 750 watt motor then :-
750 watts = 80 RPM / 60 X 2 X Pi X torque, so the full load torque is going to be 750 X 60 /80 /2/Pi = ~90Nm

That sounds about right and if I assume 80% eff at this point of operation, then the current that it would draw would be 750 /48/ .8 = 19.5 amps or 20 amps nominal.
so if I believe that, then the BBS 02 750 watt should go all day at 20 amps if I keep it at full speed ( battery permitting). Depending on what version controller you are using, the one that I am looking at has a 25 Amp current limit ( the dealer prefers to deliver it set to 20 amps) so max torque out is going to be in the region of 25/20 X 90 Nm =112.5Nm .
Those things don't scale perfectly so a claim of 120Nm at the controller limit of 25 Amps sounds believable.

One other thing ? if you use the E-brake to take power off of the motor do you have to restart the PAS ? or just start pedalling again ? or does it start up automatically when you release the brake ? Also what happens if you are in PAS 0 set to throttle only ?

Regards to all and sorry for the newbie questions.

 

[nutnspecial]

Nice work on the calcs, so it should work good then!

Ebrakes cut power when applied, and when released the controller is active again at whatever power you are calling for via inputs such as pas or throttle. At least I assume pas to be the same as my experience with throttle and ebrakes. It wouldn't be a very intuitive design if you had to restart pas everytime you use the brake(s) imo.

Have fun with the building and riding!

 

[speedmd]

Hi Bob

At your weight I would go with the HD for a bunch of reasons. My bbs02 is great for a light rider, but when slowed down on technical stuff, I would not want any more load on it. It can do it for a while, but your asking for trouble if you expect this daily. IMO Don't look back to the older models.

 

[vk4bxi]

Thanks guys for the comments and stuff.
I would like to go with the HD but....... where I live there is a limit on the motor size, the 500/750 watt is close or the same size as the 250/350 watt so I won't be too visible if I use a 750watt unit, and a number 7 could be made to look like a 2 for a casual inspection (I have a set of stamps), but the HD is a chunk larger and looks different. and of course there is a noticeable difference in the dent to the communal wallet.....and that will be noticed !

Now that I know the Nm available from the 750 Watt I can sort my gears to suit. The rear wheel cluster is a free wheel hub and not a cassette so my options are a little more limited, otherwise I would head for a 42 first gear on the back...and worry about getting my front wheel in the air !!##!! as it is with the 24 on the front and a 34 on the back I can lift the front wheel if I try hard enough with pure leg power !

Now to work on throttle options etc. Currently the local offer is for a thumb throttle which I presume has its own cable input in addition to the two E-brake leads. Is a twist grip better ? Not having a unit to play with I have to ask some dumb questions.....like how does the throttle interact with the PAS settings, does it override them or add to them ? and is having the PAS 0 set to throttle only the best idea ?

A local supplier offers combining the two E-brake units on to one lead and using the second E-brake lead for the gear change sensor. This seems to be a "good" way to go. From commentary seen in the various postings the only difference between doing it this way and using the HD dedicated gear change input would be the time delay before the drive switches on again. Have I got this correct ? and is it a big difference ?

Again sorry for dumb questions, but I was brought up believing there was no such thing as a stupid question, only a stupid ......

Regards Bob

 

[vk4bxi]

Oh dear it seems that my calculations were off !
On Ebay one of the vendors gives the BBS 02 750Watt ratings based on 112 RPM at full load and 60Nm Ouch !
Its going to squeeze things for me and I'm going to have to get down as low as possible on the front rings. (anyone done 3 front gears on a BBS drive ?)
30 teeth here I come.

 

[docw009]

I bought my 750W BBS02 last April, and it is not the latest model which I read has a new case, but it still has a connection for a gear sensor, which I didn't buy. I may experiment with a push button, but I've noted that my bike has chain clash in PAS0 that needs to be fixed first. Drive train is 12 years old. I will replace the chain, free wheel, and derailleur.

I prefer the thumb throttle, On my first bike build, I inadvertantly rolled the twist throttle while walking the bike with a live motor. Instant wheel above my head. Also, with a thumb throttle, I could use grips of my choice rather than be bound to the cheap rubber on the twist throttle. On the other hand, a thumb throttle moves the brake lever farther from your grips, and if used in conjunction with a shifter, that distance can be uncomfortable. On my BBS02 bike, I put the thumb throttle on the left and scrapped the crank shifter, I believe Throttle overrides any PAS setting by the way.

The pulling power of my BBS02 seems quite strong. especially in the granny gear. I am also an old electical engineer. Thirty meters on a 20% grade? If you did it once under manual effort, having 3-4X more power ought to be doable. If not, so you walk?

 

[vk4bxi]

thanks for your comments.
Some of the problems with the BBS XXX appears to be that there is not just one manufacturer of the controller package and not all of them are exactly the same spec.
And yes I did make it one day ....the next day I went out with a inclinometer to check what the angle was ....average 11~13 degrees or ~20% grade. Only the once though.

Regards bob