Friction *regen brake* sanity check

Based on this excellent thread:
https://endless-sphere.com/forums/viewtopic.php?f=31&t=86961

It is clear that torque exerted by the motor on 'swingarm' makes it press into the tire and provide ample engagement, but it would be impossible to use as a dedicated regen brake.

So, if I am to use a friction drive as regen brake, I'll have to turn it 180 deg (so BRAKING torque will push it into the tire), will have to resort on manual (brake cable pull say) engagement of motor to the tire, and it would be, in turn, impossible to be used in assist mode?

I'm building a long-distance tourer and having maximum efficiency to get the most out of human powered drivetrain is paramount, but I'll need a regen brake to ride down hills and extract about half of the assist watt-hours it took me to 'get there', and 'freewheeling regen braking' is not easy to implement w/o a sort of clutch (what friction drive that can be engaged and disengaged amounts to).

By the way, anyone experimented with concave, textured friction rollers? Makes a lot of sense and can be 3d printed from hard TPU I suppose.

Various concave rollers have been tried out; I don't remmeber any details. There are a lot of posts/threads about rollers around here; Spinningmagnets probably has them indexed at the top of this forum, if not directly then in one of the other index threads.


I don't really understand all of what you are trying to accomplish though. You seem to be wanting to build just an electric assist braking system...but not an electric drive assist system?

If so, then it is as you seem to be saying, easy enough to reverse the engagement directly of the roller into the tire...but unlike an assist, the generator (since it's not a motor for this) isn't going to automatically swing to touch the tire (as it can in some designs as a motor) to begin the engagement. So you would either need it to always roll on the tire (inefficient) or be cable operated (or some other mechanical engagement operated by you). There are numerous ways to do that.

If you are trying to do both, or something other than what I describe/think above, you should post the *complete* details of your project, bike, etc., so that we can help you work out a system that will do all the things you want to do.

BalorNG said:

I'm building a long-distance tourer and having maximum efficiency to get the most out of human powered drivetrain is paramount

Click to expand...

The solutions for this design goal have been very thoroughly characterized and refined over the last.. century? And they don't include unnecessary braking, but rather aero (especially for down hills), and light weight to ease up hills.

BalorNG said:

but I'll need a regen brake to ride down hills and extract about half of the assist watt-hours it took me to 'get there'

Click to expand...

This requirement generally doesn't fall within the range of desired/estimated/measured regen. It would take a very specific ride profile to produce, and possibly be disadvantageous (unnecessary braking?).

As I always say, run the numbers to see why.

fatty said:

The solutions for this design goal have been very thoroughly characterized and refined over the last.. century? And they don't include unnecessary braking, but rather aero (especially for down hills), and light weight to ease up hills.

This requirement generally doesn't fall within the range of desired/estimated/measured regen. It would take a very specific ride profile to produce, and possibly be disadvantageous (unnecessary braking?).

As I always say, run the numbers to see why.

Click to expand...

I actually did. Multiple times. *sigh*
Light is not an option. Even if I run stark naked (I'm clinically obese... ultracyclist. Sounds like an oxymoron, but here we are).
Since my options of making stuff that is strong AND light are very limited, I'll have to resort to 'strong and very heavy'. Overall system weight is expected to be about 170+ kg, with majority of that being *me*.
Aero IS an option. That's the whole point.





And it would mean that I'll hit 100+ kmh on any noticeable inline, which is cool - until it isn't. (And by 'long distance' I mean 600+ km a day).
Any other unrelated tidbits you want to share?

amberwolf said:

Various concave rollers have been tried out; I don't remmeber any details. There are a lot of posts/threads about rollers around here; Spinningmagnets probably has them indexed at the top of this forum, if not directly then in one of the other index threads.


I don't really understand all of what you are trying to accomplish though. You seem to be wanting to build just an electric assist braking system...but not an electric drive assist system?

If so, then it is as you seem to be saying, easy enough to reverse the engagement directly of the roller into the tire...but unlike an assist, the generator (since it's not a motor for this) isn't going to automatically swing to touch the tire (as it can in some designs as a motor) to begin the engagement. So you would either need it to always roll on the tire (inefficient) or be cable operated (or some other mechanical engagement operated by you). There are numerous ways to do that.

If you are trying to do both, or something other than what I describe/think above, you should post the *complete* details of your project, bike, etc., so that we can help you work out a system that will do all the things you want to do.

Click to expand...

See above post.
I'll have a drone motor powered 'crankdrive' (peaking at about 800w... disregard the huge 'chairing', I've went with a belt) as main source of assist, and likely an other *small* drone motor direct belt drive solution as to seamlessly interface with my pedalling and even out shifting gaps and modulate speed on smaller terrain undulations.

Unfortunately, and exactly *because* I've run the numbers, any 'regen brake' that cannot be disengaged from the system and is powerful enough to meaningful and efficient in operation will serve a very considerable source of drag, and despite having about 2kwh battery I expect to spend this capacity for climbing hills ONLY and even that would not be enough for hillier routes due to overall system weight, hence the need to 'regen brake' downhills - because a very heavy and very aero HPV will hit terminal velocity like a plummeting bomb... with emphasis on 'terminal'.

I still want this system to be *largely* human-powered, but I hate crawling uphills - especially given 'recumbent power penalty' that is especially steep in my case (I'm a fairly strong cyclist when I'm in my form, but my recument power is less by at least 10%, which is pretty common unfortunately)

Technically, I have plenty of space for the 'swingarm' to swing around and engage the tire from both sides, but that would require a different solution from merely using a brake handle (a servo?) and I'm not comfortable with using a friction drive as source of traction - it's not very efficient and cannot be relied upon in all conditions... one thing is having to rely on conventional brakes, and quite an other to be stranded on a hill because it's raining.

BalorNG said:

I actually did. Multiple times. *sigh*

Click to expand...

Post your numbers here for accurate advice.

Is that a mockup?
There's a lot of lower-hanging fruit.

GMAC hub motor with locked clutch: no drag and does regen.

fatty said:

GMAC hub motor with locked clutch: no drag and does regen.

Click to expand...

The GMAC does drag, due to the locked clutch that allows it to do regen.

However, just like a DD hub, you can overcome that drag by feeding the motor a tiny amount of current while rolling, just enough to overcome that drag, which costs little enough power that regen typically remains a net positive.

fatty said:

GMAC hub motor with locked clutch: no drag and does regen.

Click to expand...

It definitely drags-- more so than something like a direct drive Leaf motor, in my observation. I would count it, along with all direct drive motors, as categorically unsuitable for long distance touring. Gotta have some kind of clutch to do big miles on an e-bike, or you wind up with impractically large battery requirements.

As for the OP's plans, note that the same poor mechanical efficiency that characterizes friction roller drives (often less than 50%) applies to friction roller generators. So using one for regen braking would offer useful amounts of braking, but not commensurate energy recovery.

fatty said:

BalorNG said:

I actually did. Multiple times. *sigh*

Click to expand...

Post your numbers here for accurate advice.

Is that a mockup?
There's a lot of lower-hanging fruit.

GMAC hub motor with locked clutch: no drag and does regen.

Click to expand...

Well, if you want numbers…
120 kg – my weight (there is some decent leg muscle in there, but I can stand to lose 40 kg to be sure, yet it’s not likely to happen overnight)
I did a full randonee series (200, 300, 400 and 600) on a typical upright bike, but I was a bit younger and a lot fitter/healthier than.
Planned vehicle weight – 50 kg at the very least, unfortunately – I have 15 kg of lifepo battery so this can work at all, and there is the aerodynamic shell – which is planned to be pretty light (non structural), but still... While adding a small gas motor would likely be a more of a ‘low-hanging fruit’ indeed ultimately I want to see whether a true hybrid HPV system is possible where you use external power just to level hills AND recuperate it by regen, ‘regen pedaling’ on flats and using the bike as a trainer (which is what I’m currently doing and actually having problem to get RID of resulting charge resulting from multi-hour training sessions).
Not exactly practical, but if I wanted something ‘practical’ I’d just get a car. I do it for the challenge – it is that ‘unassisted’ hills is a bit *too much* of a challenge for me so far, and getting even MORE battery is frankly getting ridiculous (not to mention expensive!). I’m having enough of a headache in getting it to fit.
Yes, this a mockup, a rideable mockup – the joints are pretty tough, if flexy and heavy. The concept is being refined, once I’ll finalize it I’ll bond the joints with carbon fiber (no welding for me).
The shell is delayed due to COVID and other related problems, but I *should* have it by summer.
CdA of the shell as pictured (the top will be lopped off for vision) is 0.046, but I’ll be happy to have double that in practice. Still, that’s nearly an order of magnitude less than a typical touring bike/MTB ebike, and quite a bit more aero than TT bikes despite being a side of a ‘small bus’ (3 meters long). It is decently fast even with no shell, surprisingly enough (hit 50 kmh in sprint)
Here is me on early iteration prototype:
https://youtu.be/yWvE6yLxuJo

GMAC hub motor with locked clutch: no drag and does regen.

*sigh* A motor with a ‘locked clutch’ and no drag is possible (SynRM?) but we are not quite there yet, and any permanent magnet motor will have drag, and the more powerful the motor – the more drag, it is inevitable due to physics (iron losses).
I expect about 30w of no-load drag at cruising (40kmh) speed, on par with GMAC, and given running time of about 15 hours to reach my destination goals, that would be about 450 wh wasted just to ‘get even’.
I expect to regen about 1000 wh during this time (based on my numbers, assuming efficiency of 85% and data from Computational cyclist), so if push comes to shove I’ll just eat those losses, it’s worth it – given aerodynamics that is much better than ‘average’, of course.
A much smaller motor with no-load drag of 10w at cruising speed is something I’m willing to swallow, but it will not be nearly enough even to scrub speed for any noticeable (above 5%) hill. Oh gravity, though art a heartless bitch.

However, if friction drive is THAT inefficient I think I’m better off with ‘fixed gear’ (I’m using RC middrives allaround, much better value given that I have a 3d printer handy and laser cutting and bolding/bonding stuff is relatively cheap and easy).

Maybe I should do them myself once roads are cleared of ice? I presume using a shaped (and larger diameter) roller *will* make it more efficient, but I’ll have to fab it and make sure it is strong enough to withstand the loads…

If anyone has alternative ideas how a ‘clutch system’ that can withstand to about 5 nm of torque peak (‘first stage’) can be easily fabricated (3d printed, say) and operated reliably so motor can be engaged and disengaged from the wheel, I’d very like to hear them.

P.S
Did some research.

It seems that a friction drive generates a whooping 100w of drag when under full engagement… while formidable, this is still much better (due to intermittent use) than having the motor drag all the time – and since the system is self-adjusting, it should cost me about 10% of braking efficiency at worst, which is still much better than nothing, or permanent motor drag.

Also, there is more to this than meets the eye. Provided you don’t go overboard with the torque (I will not – my goal is *efficient* operation, and braking is easier than acceleration anyway – other drag forces are ‘working for you’ so to speak now), and there is no ‘roller’ slippage, the extra drag is basically additional tire rolling resistance, hence all factors that reduce it will reduce will help as well, and my tire should pretty damn good - Marathon Almotion installed tubeless.
Btw, ‘can’ of the Flipsky 6384 190kv motor I have is slightly textured, that should help too I think…

Why not an electromagnetic clutch like off an AC compressor?

BalorNG said:

Well, if you want numbers…

Click to expand...

To start, what is your estimated Wh/km at 40km/h on that 170kg bike? At double your theoretical CdA, you might get down to 6Wh/km. 600km = 3.6kWh.
What is your functional threshold? You'd need to hold >175W for 15 hours straight.


It's just a problem of scale, and as has been discussed here, at ultradistance scales, electrification becomes a liability, not an asset. Even cutting-edge LiIon energy density (230Wh/kg) is still four and a half orders of magnitude less than fat metabolism (10.5kWh/kg).

I get that you're not trying to use e-assist the whole time, but that actually makes less sense, because now you have this massive weight and complexity penalty all the time, which you're only going to make use of use.. up hills? It's circular reasoning: build a heavy ebike so you need e-assist to get up hills so you need a heavy ebike?
Just buy or build a light human-powered velomobile if you want pedal 600km.

You asked for a sanity check...

NCC1941 said:

The GMAC does drag, due to the locked clutch that allows it to do regen.

Click to expand...

Chalo said:

It definitely drags-- more so than something like a direct drive Leaf motor, in my observation.

Click to expand...

Maybe a bit of exaggeration by Grin, but they seem convinced it is less than a DD hub. Interesting.

fatty said:

NCC1941 said:

The GMAC does drag, due to the locked clutch that allows it to do regen.

Click to expand...

Chalo said:

It definitely drags-- more so than something like a direct drive Leaf motor, in my observation.

Click to expand...

Maybe a bit of exaggeration by Grin, but they seem convinced it is less than a DD hub. Interesting.

Click to expand...

Maybe at speed? I can only compare their drag in the workstand or when I'm building wheels.

fatty said:

NCC1941 said:

The GMAC does drag, due to the locked clutch that allows it to do regen.

Click to expand...

Chalo said:

It definitely drags-- more so than something like a direct drive Leaf motor, in my observation.

Click to expand...

Maybe a bit of exaggeration by Grin, but they seem convinced it is less than a DD hub. Interesting.

Click to expand...

From Grin's GMAC description:
"The GMAC motor without a clutch has a no-load drag that varies from 1.0- 1.5 Nm with sheel speed, which is more than a typical direct drive hub motor (0.6-1.0 Nm)."

fatty said:

BalorNG said:

Well, if you want numbers…

Click to expand...

To start, what is your estimated Wh/km at 40km/h on that 170kg bike? At double your theoretical CdA, you might get down to 6Wh/km. 600km = 3.6kWh.
What is your functional threshold? You'd need to hold >175W for 15 hours straight.


It's just a problem of scale, and as has been discussed here, at ultradistance scales, electrification becomes a liability, not an asset. Even cutting-edge LiIon energy density (230Wh/kg) is still four and a half orders of magnitude less than fat metabolism (10.5kWh/kg).

I get that you're not trying to use e-assist the whole time, but that actually makes less sense, because now you have this massive weight and complexity penalty all the time, which you're only going to make use of use.. up hills? It's circular reasoning: build a heavy ebike so you need e-assist to get up hills so you need a heavy ebike?
Just buy or build a light human-powered velomobile if you want pedal 600km.

You asked for a sanity check...

Click to expand...

My functional threshold is 250watts as of now, estimated by XERT on a power meter. In fact, given that I'm getting unrealistically high regen numbers (close to 100%) on my pedal generator, it can actually lower it by 10% or so (unless the system inflates my regen watts as well - which is possible, too - likely both).
My 'upright bike' power functional power was 270w a month ago, likely a bit more now - like I said, 'recumbent power penalty'.

I intend to raise it by 10 or so watts in coming months. My 'LTP' is already around 200w, I can hardly expect to pedal at 200W for *many* hours of course, yet 175w seems doable, if with difficulty.

And again, I am my own 'heavy ebike' even when stark naked. It's is a problem that so far only gotten worse and it's a vicious cycle - I get heavier, riding is harder, I get more depressed, I gain more weight, riding is yet harder - repeat.

I've already had (actually, more) weight like this, and I've managed to lose it - maybe I will now, but this is not likely to be easy and fast. Plus, I like to tinker. Technical complexity is not a problem for me, provided it does not fall apart midroute. Given that I've managed to clock 1000+ 'virtual kms' on a trainer and previous prototypes and mostly ironed out the kinks - hopefully not.

That is not exactly a 'sane' approach to the problem, I know, but I've never claimed to be the sanest person out there, yet at least I am honest about my limitations.

As for *your* numbers... you don't seem to be as good at them as you seem to be claiming, to be frank.

Let's assume my 600 km ride has 4000 meters of elevation (based on profile analysis and my previous experience riding similar routes, Russia is no Alps unless we are talking something like Caucasus, and I'm not quite ready to get here)

Assuming weight of my ride to be 170 kg, and using very simple MGH forumla and converting kilojoules to wh we get 1850 wh to fully and completely negate ALL my weight uphill over this ride, bike and battery included and turning it into a a virtual flatland.

Yea, extra weight of the bike/battery will add about 15w of rolling resistance, and you cannot expect 100% energy conversion efficiency, so it would *not* be enough after all, but that's where *efficient* regen braking downhill comes in, provided it does not all the time!

As for fat metabolism... if I could burn fats while riding uphill at 1000w, it would be great! Unfortunately, my pesky biochemistry prevents this.

A conventional velomobile is emphatically *not* an option - given our roads and drivers a very low velo with suspension that can only be charitably described as 'rudimentary' is not something that I'll enjoy using. Not to mention the small matter of costs. And it would not be light even 'unpowered', unless you further double the costs, unfortunately.

The problem is mostly aesthetic in nature.
I *like* cycling. I particularly like cycling in hilly terrain - for the views.

But I hate busting my ass uphill. Some people love it. I've never liked it even when I was decently lightweight. It is enough to ruin my enjoyment so much that I just don't find it rewarding anymore, overall. Or maybe I'm just getting old. *shrugs*

Adding assist is workable technical solution... We'll see I guess.

ilu said:

From Grin's GMAC description:
"The GMAC motor without a clutch has a no-load drag that varies from 1.0- 1.5 Nm with sheel speed, which is more than a typical direct drive hub motor (0.6-1.0 Nm)."

Click to expand...

Wow -- thanks for the correction.

BalorNG said:

I'll have a drone motor powered 'crankdrive' (peaking at about 800w... disregard the huge 'chairing', I've went with a belt) as main source of assist, and likely an other *small* drone motor direct belt drive solution as to seamlessly interface with my pedalling and even out shifting gaps and modulate speed on smaller terrain undulations.

Click to expand...

ah. then disregard whatever i said about the assist part. sounds like you've worekd out that setup thoroughly.

Unfortunately, and exactly *because* I've run the numbers, any 'regen brake' that cannot be disengaged from the system and is powerful enough to meaningful and efficient in operation will serve a very considerable source of drag, and despite having about 2kwh battery I expect to spend this capacity for climbing hills ONLY and even that would not be enough for hillier routes due to overall system weight, hence the need to 'regen brake' downhills - because a very heavy and very aero HPV will hit terminal velocity like a plummeting bomb... with emphasis on 'terminal'.

Click to expand...

some freeform thought belwo, sorry i aam too dozey to edit it to real comprehensibility. you may have already thought of all this stuff but in case you haven't:

then a disconnectable regen brake taht is as lightweight as possible is your best bet, and a friction drive may work, as long as the motor can handle the continous heat that will be created, and the battery can handle the continous charging current that will be generated. i would use a direct roller-to-motor connection, roller on the shaft, rather than a belt or chain or whatever, so you don't have any additional losses, and then us a motor with the right kv/etc to generate teh right voltage to create the regen current you need at the speed you expect to hold with it.

you'll also need to ensure hte regen brake power / torque is sufficient to provide the braking power you require on the worst case downhill with the worst case tailwind, without overwhelming the ability of the battery to absorb that power.

you also have to maek sure you are never needing this brake when the battery is too full to accept the amoutn of wh that will be generated on the whole downhill run, meaning if you ahppen to finish an uphill to reach a layover point where you recharge... you can't use the brake on the downhill, and you will need to use only your mechanical brakes.


you may also want to make some form of alarm that alerts you that the regen brake is about to cut off, with enough time for your reaction, and setup a limit on the brake so that it never fully charges the battery to the point where the bms would shut off due to being full at hvc. if the bms shuts off and he controller being used cant' stop regenning in time, the voltage can spike so high that the fets are blown up.


But if it rolls on the tire, remember that it is going to heat the tire from friction and carcass flex, so if the tire is also heated from rolling at speed and/or other braking forces against the road itself, it may affect tire inflation during and shortly after braking, and it may also affect tire longevity if it does any permanent carcass deformation or acclerates tread wear (the softer the trie compound i would guess the more that would happen, but i haven't tested any of this, it's just thoughts that pop inot my head abou stuff that happens taht you might want to check out if you ahaven't thougth of it0).

BalorNG said:

As for *your* numbers... you don't seem to be as good at them as you seem to be claiming, to be frank.

Click to expand...

Haha, how do you figure? I calculated based on the very limited information you had provided (mass, velocity, CdA, and distance) -- where was the error?

You solved an entirely different problem based on numbers you hadn't given before. What a dumb argument.

BalorNG said:

A conventional velomobile is emphatically *not* an option - given our roads and drivers a very low velo with suspension that can only be charitably described as 'rudimentary' is not something that I'll enjoy using. Not to mention the small matter of costs. And it would not be light even 'unpowered', unless you further double the costs, unfortunately.

Click to expand...

I'm genuinely confused now. Isn't this exactly what you've built and are proposing?

amberwolf said:

BalorNG said:

I'll have a drone motor powered 'crankdrive' (peaking at about 800w... disregard the huge 'chairing', I've went with a belt) as main source of assist, and likely an other *small* drone motor direct belt drive solution as to seamlessly interface with my pedalling and even out shifting gaps and modulate speed on smaller terrain undulations.

Click to expand...

ah. then disregard whatever i said about the assist part. sounds like you've worekd out that setup thoroughly.

Unfortunately, and exactly *because* I've run the numbers, any 'regen brake' that cannot be disengaged from the system and is powerful enough to meaningful and efficient in operation will serve a very considerable source of drag, and despite having about 2kwh battery I expect to spend this capacity for climbing hills ONLY and even that would not be enough for hillier routes due to overall system weight, hence the need to 'regen brake' downhills - because a very heavy and very aero HPV will hit terminal velocity like a plummeting bomb... with emphasis on 'terminal'.

Click to expand...

some freeform thought belwo, sorry i aam too dozey to edit it to real comprehensibility. you may have already thought of all this stuff but in case you haven't:

then a disconnectable regen brake taht is as lightweight as possible is your best bet, and a friction drive may work, as long as the motor can handle the continous heat that will be created, and the battery can handle the continous charging current that will be generated. i would use a direct roller-to-motor connection, roller on the shaft, rather than a belt or chain or whatever, so you don't have any additional losses, and then us a motor with the right kv/etc to generate teh right voltage to create the regen current you need at the speed you expect to hold with it.

you'll also need to ensure hte regen brake power / torque is sufficient to provide the braking power you require on the worst case downhill with the worst case tailwind, without overwhelming the ability of the battery to absorb that power.

you also have to maek sure you are never needing this brake when the battery is too full to accept the amoutn of wh that will be generated on the whole downhill run, meaning if you ahppen to finish an uphill to reach a layover point where you recharge... you can't use the brake on the downhill, and you will need to use only your mechanical brakes.


you may also want to make some form of alarm that alerts you that the regen brake is about to cut off, with enough time for your reaction, and setup a limit on the brake so that it never fully charges the battery to the point where the bms would shut off due to being full at hvc. if the bms shuts off and he controller being used cant' stop regenning in time, the voltage can spike so high that the fets are blown up.


But if it rolls on the tire, remember that it is going to heat the tire from friction and carcass flex, so if the tire is also heated from rolling at speed and/or other braking forces against the road itself, it may affect tire inflation during and shortly after braking, and it may also affect tire longevity if it does any permanent carcass deformation or acclerates tread wear (the softer the trie compound i would guess the more that would happen, but i haven't tested any of this, it's just thoughts that pop inot my head abou stuff that happens taht you might want to check out if you ahaven't thougth of it0).

Click to expand...

It would not likely be enough in all conditions, but than I'll just add 'conventional brakes' and swallow the losses, but that is likely to be very rare occurence.

People been running friction drives for a quite a while and performance in the wet aside, say that that increase in tire wear is not critical - and I'll be using it intermittenly, that also solves that overheating issue (plus I'll be using in a most efficient manner, hence - it should only get 'warm' even in continuous operation... ~1kw max on a motor rated to 4kw).

It is *highly* unlikely that I'll be able to charge more into the battery than it's max capacity - I'll have to start on a steep mountain for that...

fatty said:

BalorNG said:

As for *your* numbers... you don't seem to be as good at them as you seem to be claiming, to be frank.

Click to expand...

Haha, how do you figure? I calculated based on the very limited information you had provided (mass, velocity, CdA, and distance) -- where was the error?

You solved an entirely different problem based on numbers you hadn't given before. What a dumb argument.

BalorNG said:

A conventional velomobile is emphatically *not* an option - given our roads and drivers a very low velo with suspension that can only be charitably described as 'rudimentary' is not something that I'll enjoy using. Not to mention the small matter of costs. And it would not be light even 'unpowered', unless you further double the costs, unfortunately.

Click to expand...

I'm genuinely confused now. Isn't this exactly what you've built and are proposing?

Click to expand...

I'm talking about your general conclusion that 'adding a motor to a bike is useless for long trips'. It is most emphatically not - even a simple a motor with an overrunning clutch plus a decent battery will be able to compensate much more than it's weight over VERY long distance, you just need to use it sparingly on the hills, where application of additional power is critical for time and anaerobic effort saved.

As for what I'm building... does it *look* like a velomobile to you?
A velomobile looks like this:



They are usually trikes, rarely quads. That imply mulitrack dynamics that makes making something high enough for vision/visibility extremely challenging (my design, while no highracer, is still about a foot higher than a typical velo), adding lots of travel challening (even the best velos use elastomeric or, god forbid, friction suspension/damping for a couple cm of travel) and pretty much always run 20" wheel on front to resist cornering forces and keep provide lower.

Now, a fully faired HPV with singletrack dynamics is a different sort of challenge, but I have a few tricks up my sleeve - from platform chose (long wheelbase), aerodynamic shape (long tail) steering geometry (low trail) and a motorcycle steering damper.

If THAT fails I'll make it a leaning diamond quad with tilt lock/damping.

BalorNG said:

I'm talking about your general conclusion that 'adding a motor to a bike is useless for long trips'. It is most emphatically not - even a simple a motor with an overrunning clutch plus a decent battery will be able to compensate much more than it's weight over VERY long distance, you just need to use it sparingly on the hills, where application of additional power is critical for time and anaerobic effort saved.

Click to expand...

I don't understand why people here think physics doesn't apply to them. Please run the numbers below and let me know if you either come to the same conclusion, or what physical constraint you are ignoring.

Flat:
Let's rough your weight to 100kg and your contraption with 2kWh pack to 70kg. Your CdA 0.092 is in the range of recordholding non-electrified HPVs and just not realistic. It will be a miracle to get that to 0.138.
Source: BROL
Yields 6.8Wh/km * 600km = 4080Wh.

Compare to a non-electrified velomobile around 30kg = 130kg total, and easier to achieve CdA 0.092 = 5.2Wh/km * 600km = 3120Wh.
4080Wh - 3120Wh = 960Wh. It takes you 960Wh extra to lug around all that nonsense for your whole trip.


Hills:
170kg * 9.8m/s^2 * 4000m = 6664000J = 1850Wh. If you're able to regen at 50% you get 925Wh back. And that's only fully usable if your destination is at the top of a hill.

Non-electrified velomobile:
130kg * 9.8m/s^2 * 4000m = 5096000J = 1415Wh.
1415Wh - 925Wh = 490Wh. You save 490Wh going uphill.

925Wh - 490Wh = 435Wh. It still takes your contraption 435Wh extra.

Your argument about needing to burn 1000W while riding uphill is specious. Cyclists have been downshifting to climb hills for 100 years now to keep cranking away at FT. If your single-track streamliner is unstable at that speed, build it as a trike like most other solutions.

Obviously, these are back-of-napkin, zeroth-order approximations, but they illustrate the point.

BalorNG said:

As for what I'm building... does it *look* like a velomobile to you?

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There isn't a formal, technical distinction. A velomobile is a streetable enclosed HPV. That's what you're building, as distinct from a streamliner (which I reference above).

BalorNG said:

- and I'll be using it intermittenly, that also solves that overheating issue

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"intermittent" isn't what I would call doing downhill braking. Intermittent would be braking a few seconds here, a few there, with minutes or more in between.

Downhill braking of the type I *think* you want to do is what I would call a continuous-rating type of application.

(plus I'll be using in a most efficient manner, hence - it should only get 'warm' even in continuous operation... ~1kw max on a motor rated to 4kw).

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Remember that with RC motors (if that's what you'll be using) that power rating is normally *only* at a very high RPM, with a propeller forcing air over and thru them. If the motor you have is different, then make sure that the power it is designed to handle is under the specific conditions you'll actually be using it under.

You may well have already run all these numbers...but I prefer to bring up stuff that was obvious to someone than not to bring up what someone may not even be aware of, and have their project fail because they didn't know.

It is *highly* unlikely that I'll be able to charge more into the battery than it's max capacity - I'll have to start on a steep mountain for that...

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I just wanted to point out the potential for the problem, as people have had EVs damaged by this phenomenon (the first one I heard of was a DIY car conversion, maybe a decade or more ago). That way you know it exists, and can work out ways to avoid ever encountering it.

If you start at the top of a slope with a full battery, then go downhill braking without having used the battery, you *can* overcharge it, or at the least you can cause the BMS (if any) to turn off the input for HVC, which can potentially blow up the controller of the braking motor, due to the current suddenly having nowhere to go, which causes voltage on the controller to sharply and rapidly rise (nearly instant), and that voltage can be higher than the FETs and LVPS in the controller can handle.