Another build idea - Pinion drive with a Gates CDX belt, to a geared rear hub motor

[ncmired]

This build idea is just a thought I've had, here and there, over several years. No, I don't need another bike or build ... really, I don't.

So, you take one of these Priority 600 bikes with its 600% mid gearbox:

Add this Gates single speed freewheel and a handful of freewheel spacers:

Then, you find a reputable (probably Bafang) 135mm O.L.D. disc brake geared hub motor with a single speed thread stub. And this is where I get stuck, because I've not come across a specification chart for geared hub motors. It would also need to be small to mid-size power wise, so to not overstress the possibly Paragon-compatible dropouts.

I'm also stuck on the cadence / torque sensor that would, I presume, need to be attached to the pinion drive.

Maybe it's best that I haven't been able to complete the technical thought(s) here. And besides, no funds are available.

[AZguy]

That gearbox does sound like a very cool idea - 600% range would be awesome although I really don't want for much with the >450% I've got presently... I'd still take it!

[ncmired]

One of the things that intrigued me about the Pinion's 600% range is that it might accommodate slow (stomper) and fast (spinner) rider cadences, matching up to the motor's power "window".

[ncmired]

Yep, that's dang good, for an old buzzard with one leg - if you don't mind me saying so ;-). And says the old phart with some aftermarket internals.

Lemme ask you a question on our motors. "Bogging" the motors down, yes bad as it generates eddy inefficiencies as heat overload, but then where's the bottom of the RPM efficiency spot? I think it's around 75-80% of the unloaded max RPM, or is it less? So, take the box stock BBSHD, winding out at 150RPM unloaded - does the sweet spot start at 112.5 RPM (75%)? Now let's move on to the Ludi V2, which spins the motor past 180RPM unloaded - 135 RPM (75%)?

[AZguy]

I really don't know where the efficiency maxes, etc. but I wouldn't be surprised if there isn't something out there and marcos might have some insight too, even with the stock controller he knows these motors likely as well if not better than just about anyone

FWIW with a 52V battery with a high'ish SOC I've measured well over 150rpm (can't remember exactly, may have made a note somewhere) - I'm guessing that's closer to a 48V battery at 50-70% SOC - maybe Marcos knows the kv rating on these which would hone that in

I had always shot for not running more than 500-750W continuously at less than 50rpm... granted it's completely arbitrary and I have zero data to support that aside from having done it in the AZ heat... and 50rpm made sense considering my bike gearing and that all I was doing continuously before the new leg was 50-60rpm =]

[Mike_V]

Cadence seems to me a 'hot button' topic of discussion because an unpowered bicycle ( of course ) requires hub engagement and muscle power.
Riders are 'used to it.'
"Ghost pedaling" or choosing pedaling cadence on a mid drive is a great option as I ride, for example:
I'm tired and low voltage but want to go on without throttle until I recover or
For any reason:. Ex because it runs good on today's entire route, no gear changes just kick my feet and watch the world go by.

[ncmired]

Much agree on limiting watts when you know the motor is spinning slow. When I first read about the BBS02, the early entrants and/or reviewer often felt that it needed another gear down stage. This sentiment was repeated, even more so, when the BBSHD came out. Kinda, if you're gonna dump max power into the motor, let it spin fast, which likely means you're not going to be able to keep up or contribute to it (with your measly 150 watts of leg power)(so just enjoy your throttle). Also I'd guess: if you are able to keep up with the motor cadence and contribute some pedal force at high PAS settings, the motor is probably bogging, making heat, and wasting battery.

[AZguy]

I think much more reduction and the motor (actually the reduction gears) would get too big... it's already a two stage reduction to get where it's at and the secondary output gear is what's driving the case size at the crank

It would be nice - I just don't think it may be practical

[Mike_V]

OK but there's no need to keep up, it just keeps cranking faster as chosen by power level selection.

[Dshue]

With a torque sensing system it would be worth it but with cadence sensing there would be no real benefit of having a pinion drive.

[ncmired]

With a torque sensing system it would be worth it but with cadence sensing there would be no real benefit of having a pinion drive.

Hi Dshue - if you don't mind, can you gimme more rational on this thought.

I've been having a few late night mind churns on "amplifying the clumsy human leg sorta sine wave power output" via the motor and turning it into a relatively smooth, constant wheel RPM and non-jerky feel, especially as the amplification level goes up.

For example, is the Bosch torque sensing system often considered the best not because of the motor / software design, but more because the system is relatively low power compared to what we're used to having?

Perhaps a question for Marcos would be (on the M600 V2 controller), in torque mode does he have to calculate then fill in some power during the lulls in leg-driven power.

Perhaps I just need to find another hobby, or play cards with the old folks more.

P.S. Apologies for my helter-skelter thoughts scattered into this thread. I won't get into the others, such as "stealth" e-bikes are stealth to no one and air-peddling looks and feels really stupid (yes, I do it at times, and maybe it helps the muscles recover).

[AZguy]

Going by feel, on the torque sensing units I've ridden they seem to smooth the cycle out but with my asymmetrical leg power, at low rpm's I could definitely feel some backing off from as I'd get to the leg "that just goes along for the ride" was doing the "pushing" (or lack thereof) and didn't care for that *at all*... it didn't seem bad at higher rpm's but down in the 50-60 was very noticeable to me... it might be a tune in setups noticed in the ultra programming tool some time based entries for the torque sensor.

Having said that I didn't like torques sensing even pedaling fast enough not to feel any surging. I don't want to have to change my force in order to change the motor force... not at all, not one bit... I either want the predictable PAS or even more predictable throttle...


I'm interested in Dshue's response... doesn't make a lick of sense to me why it would matter with a pinion drive whether torque or cadence sensing... from the user standpoint it ought to be transparent, no different than an IGH from the riding perspective... it's just on the crank instead of the rear hub...


But even after all that unless it was integrated with a mid drive I likely won't ever be using one since I just plain don't like hub drives even more than I don't like torque sensing lol

[Dshue]

Because most cadence hub motor systems are on and off. All it wants to do is reach its max predetermined speed. Just about any gearing is good enough for that.

At least with torque sensing you can validate the Pinions purpose somewhat.
From my experience with hubs and mid drives I get good pedal feedback feel from a mid drive as I'm pedaling through a pas level. On the hub motors I've ridden there is very little pedal feedback feel.

Maybe if you were wanting to pedal with 0 assist a lot then the Pinion could be useful with a cadence system. Or if you only intended to use assist to start moving.

[Dshue]

Yeah the pinion system is like an igh. But it doesn't change the fact that as it is the cadence switch location you aren't going to go through the gears like you would with a mid drive. The hub drives pas system has to have a speed limit, no matter if they are increments assigned to each level or just the max speed the system allows. With a mid drive max speed is going to be different depending on the gear you're in. With the hub system speed is not in anyway associated with gear selection. Pas WILL go to the highest speed it is allowed to and it doesn't make a difference what gear you have the pinion in. If the system allows for 28mph in pas then that's the speed you will go in pas no matter how easy or hard, fast or slow you pedal. The only time the pinion gearing will make any difference is if you pedal over the systems max speed limit.

[ncmired]

Thanks much, guys - here again is the ultimate desire - not a sensible desire necessarily, but again just a thought experiment: [the pinion drive between the rider and the motor] might accommodate slow (stomper) and fast (spinner) rider cadences, matching up to the motor's power "window".

Let's say the PAS isn't current restricting the motor, and since it's a 500 watt motor it can (by itself) roll the bike on flat ground, no wind, etc. in the low twenties - the actual speed doesn't matter. What I'd like the Pinion drive to do is to match the rider's available leg power and cadence abilities to assist the motor, regardless whether the rider is a stomper (higher pinion gear) or a spinner(higher pinion gear). If/when a slight incline is met, the rider "oomphs" a little more till he gets to the other side.

If you drop the PAS, limiting the motor current, I think the above still happens.

Again, just a thought, and not a bike I could afford to build as an experiment, nor would the end result fit my terrain.

[AZguy]

Sure, my hub bike is speed limited by the battery voltage

My mid is also "speed limited" by the battery voltage (or maximum power) and the top gear but it's at a pedal cadence that's far too high for me to pedal and since I always pedal it's fair to say that it's unlimited speed since I don't ever hit any programmed speed limit... I don't like controllers that speed limit before the battery... not at all... different discussion tho IMO

I still don't see how any of it matters regarding whether a pinion drive (crankset gear system) vs. IGH or even cassette - they all behave the same way in the end... managing the reduction between pedals and rear wheel... The tension on the drive line is different but that doesn't matter from the rider perspective and aside from that everything else is the same...