Current Avinox MG Prototype Bikes Don't Support Battery Regen

[Ndanger]

I expect that if battery regeneration is light, reliable, reliable and uncomplicated to maintain it might be the useful in some scenarios. But non of these are likely.

 

[TorAtle]

the mere presence of chain tensioner disqualifies reverse tension on the belt/chain that is essential to battery regeneration

You could have 2 tensioners, one for each direction?

 

[slickrock]

You could have 2 tensioners, one for each direction?

That would be exactly what you don't want. The point is to have zero-tensioned slack on the chain/belt to drive power transfer. The top half of the chain loop is completely handled by pedal or motor slack take-up (for what little there is) and as long is there's forward momentum, there is zero-tensioned slack. Tensioner up top just wouldn't make sense.

On an a derailleur system, the derailleur takes the tensioner role for the bottom half of the chain, only, and takes up all that chain slack to support the dish-sized gear cluster in the the cassette. For dual suspension MTB/EMTB, this importantly does double duty by taking up chain growth that befalls nearly all the dual-suspension designs out there. For MTU systems (MGU/ECVT/PBW), you need that spring tensioner solely for the purpose of taking up chain slack due to the chain growth for dual suspension as it goes through its travel. If the bike had regen then forces at the generator would take up slack, fully extending the tensioner and pull the rear suspension back down, creating ridiculous anti-squat and chain snap. So the point it to remove all slack in the chain/belt loop so the drive/generator forces can operate symmetrically: all spring tensioners must be gone. Which IMO is actually a good thing. That's why I'm a fan of concentric-pivot designs for gearbox/IGH MTB and ECVT/MGU/PBW for EMTB - you can ditch the tensioner for good. And ditch Ochains and Sidekick hubs for good as well since there is no pedal kickback or chain whipping.

 

[sethimus]

there is a reason why there were so little mtbs with concentric pivots and the brands who built them were not successful

 

[slickrock]

there is a reason why there were so little mtbs with concentric pivots and the brands who built them were not successful

That they are rare is an indication that either they have undesirable/suboptimal characteristics or that other designs are better or both. Please elaborate so I can address each issue.

 

[sethimus]

That they are rare is an indication that either they have undesirable/suboptimal characteristics or that other designs are better or both. Please elaborate so I can address each issue.

most of them were used on slopestyle bikes lately only, because they pedal like shit. and they wont be used on ebikes either because there is no way to mount the chainstay

 

[Ndanger]

Just as a concentric pivot offered real technical advantages but didn't make conventional suspension obsolete, an e-CVT may offer clear benefits without making derailleur drivetrains disappear. As for Regen, I will probably be riding a flying emtb before one with the ability to regenerate while riding downhill... but I hope to be proven otherwise.

 

[slickrock]

most of them were used on slopestyle bikes lately only, because they pedal like shit. and they wont be used on ebikes either because there is no way to mount the chainstay

Not if they are high-pivot. Elevated chainstays help (like the Mondraker prototype), but is not required for chain. But if using belt, you would need either elevated chainstay, or Horst Link to separate the chainstay from seat stay during installation. For folks with a belt fetish, VPP and DW Link style suspensions will fall out of favor.

My main issue with concentric pivot for me is that anti-rise is in lockstep with anti-squat. If you tune for higher anti-squat with HP, you also get high anti-rise. Many actually prefer excessive anti-rise, but I'm personally prefer mid to low mid anti-rise (which is why I prefer Horst Link derived suspensions and six-bar animals like Sixfinity). The only way I know to get around this for concentric pivot is a floating rear brake, which I would take in a heartbeat over necessitating a freaking spring tensioner with a more traditional 4-bar layout. I truly hate them.

 

[TheKaiser]

That they are rare is an indication that either they have undesirable/suboptimal characteristics or that other designs are better or both. Please elaborate so I can address each issue.

Sethimus may have his own ideas about what made them bad, but from my experience on concentric pivot bikes, the pedal bob was insane, due to the lack of antisquat. This was back in the day, when bike designers/engineers were still figuring out what made a bike pedal well, and some of them latched onto the idea that, because there was no chain growth on the concentric bikes, there could be no loss of energy, because the suspension was unaffected by chain tension.

Early Pole bikes were actually concentric and there were threads on MTBR (you may be able still find them) where Leo from Pole was arguing with people, with him taking the above mentioned stance (although he didn't originate it), and saying that bikes with what would come to be called anti-squat (I don't think the term was yet in common use in regard to bikes, if memory serves) were actually the ones losing energy, because some of the chain tension was being wasted "holding the suspension up" rather than going toward forward propulsion. He also thought that, as long as the movement was basically undamped, no energy would be lost to heat, so he advocated against trying to reduce the movement with increased compression damping. It kind of makes some intuitive sense, from an armchair theory standpoint. What I think he and the other concentric advocates were forgetting was the pulsative nature of a rider's power application, and the need for the rider to have a platform to "push against" especially when pedaling standing or sprinting.

I spent a fair bit of time on a Rotec like in the attached pic, and WOW did it feel terrible when pedaling, even when compared to other bad pedaling downhill bikes of the era, and it cycled deep into the travel with each pedal stroke.

Now having said all of that, on an eMTB, the motor is reducing the pulsative nature of the power application substantially, potentially making concentric more viable. Also, just having the motor makes a bad pedaling bike less of a concern, which is what makes our 50lb bikes with enduro/DH tires tolerable on an XC ride. The lack of anti-squat would still mean it would bob a lot from rider body movement when pedaling, particularly when standing, but, if that proved to still be intolerable, it could potentially be minimized with either some sort of electronic suspension like Flight Attendant or Live Valve, or simply a more sophisticated damping tune (bikes in that Rotec era had nearly no compression damping). You might lose some rear suspension sensitivity as a result, but maybe the improved sprung/unsprung mass ratio from the MGU/MTU would offset that. I'd be willing to give one a try, but without throwing a leg over one, I dunno how all those factors would balance out., vs. the status quo.

 

[slickrock]

Sethimus may have his own ideas about what made them bad, but from my experience on concentric pivot bikes, the pedal bob was insane, due to the lack of antisquat. This was back in the day, when bike designers/engineers were still figuring out what made a bike pedal well, and some of them latched onto the idea that, because there was no chain growth on the concentric bikes, there could be no loss of energy, because the suspension was unaffected by chain tension.

Early Pole bikes were actually concentric and there were threads on MTBR (you may be able still find them) where Leo from Pole was arguing with people, with him taking the above mentioned stance (although he didn't originate it), and saying that bikes with what would come to be called anti-squat (I don't think the term was yet in common use in regard to bikes, if memory serves) were actually the ones losing energy, because some of the chain tension was being wasted "holding the suspension up" rather than going toward forward propulsion. He also thought that, as long as the movement was basically undamped, no energy would be lost to heat, so he advocated against trying to reduce the movement with increased compression damping. It kind of makes some intuitive sense, from an armchair theory standpoint. What I think he and the other concentric advocates were forgetting was the pulsative nature of a rider's power application, and the need for the rider to have a platform to "push against" especially when pedaling standing or sprinting.

I spent a fair bit of time on a Rotec like in the attached pic, and WOW did it feel terrible when pedaling, even when compared to other bad pedaling downhill bikes of the era, and it cycled deep into the travel with each pedal stroke.

Now having said all of that, on an eMTB, the motor is reducing the pulsative nature of the power application substantially, potentially making concentric more viable. Also, just having the motor makes a bad pedaling bike less of a concern, which is what makes our 50lb bikes with enduro/DH tires tolerable on an XC ride. The lack of anti-squat would still mean it would bob a lot from rider body movement when pedaling, particularly when standing, but, if that proved to still be intolerable, it could potentially be minimized with either some sort of electronic suspension like Flight Attendant or Live Valve, or simply a more sophisticated damping tune (bikes in that Rotec era had nearly no compression damping). You might lose some rear suspension sensitivity as a result, but maybe the improved sprung/unsprung mass ratio from the MGU/MTU would offset that. I'd be willing to give one a try, but without throwing a leg over one, I dunno how all those factors would balance out., vs. the status quo.



View attachment 187778

I guessed you missed my point about High-Pivot. Those bikes your rode were low pivot pretty much at BB Level, and as you say nearly zero anti-squat. Besides this kind of pivot location is pretty much impossible with any mid-motor EMTB.

I'm referring to high-pivot concentric pivot suspension like this bike:

You get your anti-squat , with no pedal kickback and no chain tensioner (yah!). And the main pivot is above where the mid-drive MGU would be where there is room. IMO, this is the cleanest suspension design for future ECVT bikes. And you get battery regen too.

 

[sethimus]

I guessed you missed my point about High-Pivot. Those bikes your rode were low pivot pretty much at BB Level, and as you say nearly zero anti-squat. Besides this kind of pivot location is pretty much impossible with any mid-motor EMTB.

I'm referring to high-pivot concentric pivot suspension like this bike:

View attachment 187798
You get your anti-squat , with no pedal kickback and no chain tensioner (yah!). And the main pivot is above where the mid-drive MGU would be where there is room. IMO, this is the cleanest suspension design for future ECVT bikes. And you get battery regen too.

now replicate that with a motor, only possible with 2 chains/belts like pivot‘s dh bike…

plus you get issues with packaging everything as motor spindles are still wider. which means you can just use an idler and be done with it, as the extra resitance will probably be lower than using 2 chains/belts anyways, so what exactly did you gain?

 

[Vision_Tim]

Regen is kind of dumb on MTB because are we really slowing down that much downhill to be worth the squeeze on this? Why not just toss on a little alternator so you can recharge on manual mode while you ride not under power? Sure it will take up more room but endless range. I'm mostly kidding here except for the first part.

 

[DirkWisely]

Regen is kind of dumb on MTB because are we really slowing down that much downhill to be worth the squeeze on this? Why not just toss on a little alternator so you can recharge on manual mode while you ride not under power? Sure it will take up more room but endless range. I'm mostly kidding here except for the first part.

A significant portion of the energy you spent going uphill is burned up as heat going downhill. If your terrain is at all steep you're bleeding most of your energy as heat in the brakes, rather than to rolling resistance/wind resistance.

 

[Ndanger]

One of the primary reasons I am a fan of the concept of regen is to take the load off of my sore hands and arms on decents, having said that... there is a bit of a headwind to consider.

The core idea is that regenerative braking recovers kinetic energy, and kinetic energy scales with mass so the heavier the vehicle, the more energy there is available to recover.

The physics: A loaded heavy vehicle carries a lot of kinetic energy at speed, so when it decelerates, a meaningful chunk of energy can be converted back to electricity instead of being wasted as heat in the brakes. That recovered energy is large in absolute terms, and it's also large relative to the vehicle's total energy budget per trip, so it noticeably extends range.

An eMTB and rider together might total somewhere around 90-110 kg, versus a car at 1,500+ kg or an e-cargo bike hauling groceries at 150-200 kg. At comparable speeds, that's an order of magnitude less kinetic energy to recover. On top of that, several other factors stack against regen gains.

Trail riding involves frequent, low-speed, short decelerations rather than the long, high-speed braking events (highway-to-stop, downhill runs) where regen shines. Each regen event on an eMTB recovers a small absolute amount of energy.

There are real losses in the regen path itself / motor and controller conversion inefficiency, plus drivetrain/mechanical losses and those losses eat a fixed-ish percentage regardless of vehicle size, so they take a proportionally bigger bite out of a small recovery event.

Regen on a heavy vehicle is recovering a big fraction of a big number, while regen on an eMTB is recovering a small fraction of a small number, and that small number is also a small fraction of the eMTB's total energy. It's not that regen "doesn't work" on a light bike, it's that the physics of mass scaling combined with how/where the energy actually gets spent (climbing, not cruising) makes the payoff marginal compared to the engineering complexity and added weight/cost of including it.

 

[DirkWisely]

One of the primary reasons I am a fan of the concept of regen is to take the load off of my sore hands and arms on decents, having said that... there is a bit of a headwind to consider.

The core idea is that regenerative braking recovers kinetic energy, and kinetic energy scales with mass so the heavier the vehicle, the more energy there is available to recover.

The physics: A loaded heavy vehicle carries a lot of kinetic energy at speed, so when it decelerates, a meaningful chunk of energy can be converted back to electricity instead of being wasted as heat in the brakes. That recovered energy is large in absolute terms, and it's also large relative to the vehicle's total energy budget per trip, so it noticeably extends range.

An eMTB and rider together might total somewhere around 90-110 kg, versus a car at 1,500+ kg or an e-cargo bike hauling groceries at 150-200 kg. At comparable speeds, that's an order of magnitude less kinetic energy to recover. On top of that, several other factors stack against regen gains.

Trail riding involves frequent, low-speed, short decelerations rather than the long, high-speed braking events (highway-to-stop, downhill runs) where regen shines. Each regen event on an eMTB recovers a small absolute amount of energy.

There are real losses in the regen path itself / motor and controller conversion inefficiency, plus drivetrain/mechanical losses and those losses eat a fixed-ish percentage regardless of vehicle size, so they take a proportionally bigger bite out of a small recovery event.

Regen on a heavy vehicle is recovering a big fraction of a big number, while regen on an eMTB is recovering a small fraction of a small number, and that small number is also a small fraction of the eMTB's total energy. It's not that regen "doesn't work" on a light bike, it's that the physics of mass scaling combined with how/where the energy actually gets spent (climbing, not cruising) makes the payoff marginal compared to the engineering complexity and added weight/cost of including it.

I'm not sure an electric car recovers more energy from regen proportional to its size than a bike. Yes, there's way more energy available, but it also requires way more energy to accelerate.

 

[sethimus]

to take the load off of my sore hands and arms on decents

easy, stop using shit brakes and shit suspension

 

[Diby2000]

The effectiveness of regen braking as a complete system will ultimately come down to (as everything does) how well it can be implemented. There may be extra weight penalties an possible efficiency sacrifices to enable this. I like the idea of capturing some of the otherwise wasted energy but it will come down to the details.

 

[Diby2000]

One idea (might be silly, but an idea) to enable these mid drive systems to capture kinetic energy might be to have a small gear system in the rear hub that reverses the chain direction from the wheel rotation direction. This could be done by having (another small) planetary gearset in the rear hub that is connected to the wheel (rotating forward) the brake disc (rotation speed relative to the wheel could be modulated using conventional brake systems) and the chain sprocket.
I have not thought this through completely, but enabling this could work something like:
1. Chain is being spun by the pedals/drive system - sprag clutch engages and the hub is locked (as per normal hub)- drive goes to the wheel.
2. Wheel is spinning forward (bike direction forward), brake rotor rotating at the same speed as the wheel sprag clutch disengaged - free wheel - note brake rotor spinning at the same speed as the wheel at this point and the chain stops turning.
3. Apply brake as normal - this will slow the brake rotor rotation compared to the wheel rotation. The gearing will then transform this difference in rotational speed to an opposite rotation at the chain (chain will be turning backwards). This reverse rotation at the drive unit can then be captured as regen.

 

[slickrock]

now replicate that with a motor, only possible with 2 chains/belts like pivot‘s dh bike…

plus you get issues with packaging everything as motor spindles are still wider. which means you can just use an idler and be done with it, as the extra resitance will probably be lower than using 2 chains/belts anyways, so what exactly did you gain?

In sethimus snarky prose: "Read my OP again, but this time read it slowly. "