How to figure the RPMS of your mid-drive motor.

[n00b]

Okay, so here's something I figured out that I think needs to be shared.
So, if you know your max speed, and gear ratio, you can plug it in here:

Bicycle Gear Ratio, Cadence, and Speed Calculator - Cycling Road

To use the bicycle gear ratios calculator, follow this step. Choose the size of your bike wheel and the size of your tires, then input your preferred cadence,

cyclingroad.com

Input your gear ratio and top speed and you can figure out your cadence. Probably only works for mid-drives.
I use uh..DigiHD to calculate top speed. (gps speed app)
All you do is play with the cadence until it aligns with your top speed. Or thereabouts.
For example, I plugged in the BBS02 I'm running, and it's 75, with a 53-15 gear ratio, which is pretty sad.
The same setup with a BBS03 gave me 115 rpm.
The BBS02 is probably damaged. It's had things..done to it.
Yep, that's about what it adds up to. 24 mph.
And noisy. It probably got cooked.
Same setup with a BBS03 and 58-15 did 37 mph.

 

[OlderGiantFan]

For example, I plugged in the BBS02 I'm running, and it's 75, with a 53-15 gear ratio, which is pretty sad.
The same setup with a BBS03 gave me 115 rpm.

So is that 115 RPM at the chainring?

What I'd like to know is what is the optimum efficient motor rpm, roughly speaking. Is a BBS02/HD more efficient at 3/4 max speed, half max? It would be nice to have an idea because I can cruise at 25 km/h on flat terrain in a variety of gears, but which gear should I choose, what engine RPM to give me the longest range. I can tell by ear, by feel, the RPM roughly speaking. Is half max more efficient than max?

I asked this question here once before and someone came back with some link to a complex calculator, which was useless. I wonder if anyone actually knows? If anyone has put a middrive under load and tested current drain at various rpms. varying load as the gears vary like in the real world.

 

[ak136]

Higher rpms should give you higher efficiency, so finding a gear that is good for your target speed and has enough torque at that rpm

 

[hillslayer@]

So is that 115 RPM at the chainring?

What I'd like to know is what is the optimum efficient motor rpm, roughly speaking. Is a BBS02/HD more efficient at 3/4 max speed, half max? It would be nice to have an idea because I can cruise at 25 km/h on flat terrain in a variety of gears, but which gear should I choose, what engine RPM to give me the longest range. I can tell by ear, by feel, the RPM roughly speaking. Is half max more efficient than max?
imim
I asked this question here once before and someone came back with some link to a complex calculator, which was useless. I wonder if anyone actually knows? If anyone has put a middrive under load and tested current drain at various rpms. varying load as the gears vary like in the real world.

The Grin simulator has bbso2 and hd options. I use it just to figure which gear is best for a top speed hill climb. Usually the most efficient gear is on the edge of ghost pedaling, if you slow the cadence down to much the motor starts to get hotter.

 

[OlderGiantFan]

Yeah that's the complex link I was referring to HS. I went back there and punched in the numbers and got this



As you can see it has Peak Efficiency at 40 km/h for running in a high gear on level ground, motor only, 70% throttle. But that's nonsensical! The wind drag at 40 is murderous on an upright mtb. How could the motor be more efficient there? When I talk of efficiency I'm talking about power drain on the battery and I know from experience the motor is hauling massive current out at that speed. Whatever that simulator is referring to it's not the information I'm seeking.

I simply want to know "basically" what motor rpm is most efficient at 25 km/h, my cruising speed, so I can pick the right gear to minimize battery drain. Or does the motor not consume more power at varying rpms, all else being equal? Is it just as efficient lugging along at 10% of max rpm as it is at 100%? I wouldn't think so.

From the Grin page

Green Plot:

This is the efficiency curve for the electrical drive system. It is a ratio of the mechanical power coming out of the hub motor to the electrical power going in to the controller. This ratio accounts for losses inside the controller and the hub motor, but it does not include losses due to the internal resistance of the battery. Notice though that efficiency does not necessarily mean better range or less battery usage; a fast and powerful setup running at 80% efficiency may draw more power to cover the same distance as a slower arrangement at 75% efficiency.

There are many web pages on the issue but they all seem to muddy the water with pedal assist data. Useless! All I have to do is go up a gear and start pedaling harder than motor input and all the figures are different. You can't quantify that, not without a power meter that only records your leg input.

I think I'll just go with this AI dribble, and my gut feelings.

E-bike motor efficiency is generally highest when the motor runs at 75% to 85% of its maximum unloaded RPM. At this range, the motor generates less heat and converts more battery energy into motion rather than wasting it. For most riders, this translates to maintaining a pedaling cadence of 60–90 RPM for mid-drives, or keeping a steady speed of 12–16 mph (19–26 km/h) for hub-drives

That's sort of what I'm doing now anyway. 25 km/h and back off the throttle a bit. Would be nice if they had an Economy gauge on the display like they have in most cars now. A realtime current measurement displayed. I know this sounds pedantic but most of my riding is throttle only and on level ground. The more efficiency the more territory I can explore, and the less "range anxiety" lol. One good thing is the ability to pedal. Some months back I was way out on a ride and the battery got a little too depleted because I was playing on a road full of cane toads and found it best to ride over them at higher speeds. I won't say I was aiming for them, but I won't deny it either... Coming home I just used some added pedal power and got back fine.

 

[n00b]

So is that 115 RPM at the chainring?

What I'd like to know is what is the optimum efficient motor rpm, roughly speaking. Is a BBS02/HD more efficient at 3/4 max speed, half max? It would be nice to have an idea because I can cruise at 25 km/h on flat terrain in a variety of gears, but which gear should I choose, what engine RPM to give me the longest range. I can tell by ear, by feel, the RPM roughly speaking. Is half max more efficient than max?

I asked this question here once before and someone came back with some link to a complex calculator, which was useless. I wonder if anyone actually knows? If anyone has put a middrive under load and tested current drain at various rpms. varying load as the gears vary like in the real world.

That's 115 at the chainring, yes. "Cadence" if you will. All assessments are based at top speed in highest gear and under load.
Just before you're gonna ruin the motor, which I think I did to that BBS02, probably controller failure and it fried a bit.

 

[OlderGiantFan]

That's 115 at the chainring, yes. "Cadence" if you will.

I have a relatively sml to med chainring, 42T, and my smallest practical rear sprocket is 13T, but there is no way I can match the cadence of the BBS02 in PAS-2 even with that gearing. That's 2 out of 5, the standard PAS setup. It's gotta be over 200W. I guess what I'm saying is that unless I ran a much larger chainring I'll never be able to input any human power when I'm scooting along in anything but PAS-1. I think that's what probably led me to just use throttle only from the outset. And why the hell pedal anyway when you have other bikes for that. Perhaps one day I'll do some really long rides and need to pedal? But I doubt it with a fleet of motorcycles sitting in the Garage.

 

[hillslayer@]

Yeah that's the complex link I was referring to HS. I went back there and punched in the numbers and got this

View attachment 387460

As you can see it has Peak Efficiency at 40 km/h for running in a high gear on level ground, motor only, 70% throttle. But that's nonsensical! The wind drag at 40 is murderous on an upright mtb. How could the motor be more efficient there? When I talk of efficiency I'm talking about power drain on the battery and I know from experience the motor is hauling massive current out at that speed. Whatever that simulator is referring to it's not the information I'm seeking.

I simply want to know "basically" what motor rpm is most efficient at 25 km/h, my cruising speed, so I can pick the right gear to minimize battery drain. Or does the motor not consume more power at varying rpms, all else being equal? Is it just as efficient lugging along at 10% of max rpm as it is at 100%? I wouldn't think so.

From the Grin page





There are many web pages on the issue but they all seem to muddy the water with pedal assist data. Useless! All I have to do is go up a gear and start pedaling harder than motor input and all the figures are different. You can't quantify that, not without a power meter that only records your leg input.

I think I'll just go with this AI dribble, and my gut feelings.

That's sort of what I'm doing now anyway. 25 km/h and back off the throttle a bit. Would be nice if they had an Economy gauge on the display like they have in most cars now. A realtime current measurement displayed. I know this sounds pedantic but most of my riding is throttle only and on level ground. The more efficiency the more territory I can explore, and the less "range anxiety" lol. One good thing is the ability to pedal. Some months back I was way out on a mride and the battery got a little too depleted because I was playing on a road full of cane toads and found it best to ride over them at higher speeds. I won't say I was aiming for them, but I won't deny it either... Coming home I just used some added pedal power and got back fine.

Back when I was a single Bbso2 mid- drive, I would run a 36 t with a 11 to 46 t . On hill climbs that had more vehicles than I like it was full power max speed up it keeping a high cadence otherwise the motor gets hot. Most the other riding was done below 500 Watts and that would save battery. Nowadays it's just bigger battery and don't worry about speed.

 

[OlderGiantFan]

Most the other riding was done below 500 Watts and that would save battery. Nowadays it's just bigger battery and don't worry about speed.

Yeah, well I'm still in the noob 500W stage, shepherding my power, keeping at or below 25 km/h most of the time. The battery in the bike is a 48V 11.6-Ah, and must be at least 10 years old but it still holds a good charge. In 5 years since I bought the bike used I've only cycled it probably 30 times though, and always 'stored' it below 50%. When I finish my new bike with it's Bafang HD and new battery I'm sure I'll be in for a shock

 

[n00b]

I have a relatively sml to med chainring, 42T, and my smallest practical rear sprocket is 13T, but there is no way I can match the cadence of the BBS02 in PAS-2 even with that gearing. That's 2 out of 5, the standard PAS setup. It's gotta be over 200W. I guess what I'm saying is that unless I ran a much larger chainring I'll never be able to input any human power when I'm scooting along in anything but PAS-1. I think that's what probably led me to just use throttle only from the outset. And why the hell pedal anyway when you have other bikes for that. Perhaps one day I'll do some really long rides and need to pedal? But I doubt it with a fleet of motorcycles sitting in the Garage.

The BBS02 I'm using right now is only getting 75rpm and I think it's damaged, on a nice Fuji road bike. It has a whine to it.
Could swear it used to go faster.
I could replace it with a TSDZ8 and get a little more, or..put the TSDZ8 on a bike with suspension forks and a 52v battery (Fuji is 36v battery) and will take babompa bompa diamond tread tires and stop better. Leaning towards the latter.
One of those 2 bikes is going to have to sacrifice something for now.
I'm thinking pull the back rim and BBS02 and derailleur off the Fuji

Leave the throttle and controller and battery, get a TSDZ8 and another cassette rear wheel later.
29er with fat tires and kool stop side pull brakes vs. that, and it goes faster and stops faster.
Oh, and keep the BBS02 for bench testing setups, because it's good for that.
Actually took the 52v battery off the road bike because it was too much.

 

[OlderGiantFan]

Looks like that chain is too short perhaps?

 

[n00b]

Looks like that chain is too short perhaps?

Yes, but it's good enough like that. With 36v 30A bettery, I just lock out the lower ones.
I already broke one of those cassettes by using the black ones. Exploring other options at this moment.
I put a Shimano something to 41T on the one that broke, but it's a BBS03 with an adapter so now I need spacers and long bolts to move the chainline.
The plan was to put the tsdz8 on the Fuji, but I want to rig something up where me and my buddy can go through the woods. The Fuji thing is just something I've been on about since I was around 19.
Hybrid 28" road bike. For whatever reason, the last one had a BMX-type bottom bracket. It's a nice bike, gonna have to get back to that later. Edit: I went to a 56 on the front, now it gets onto the 1st black one.
The 56T chainring will stay with that bike. I can pedal it faster than that particular BBS02 will pull it.
The plan was to put the Tongsheng on it, but just paid bills and am po.