Series Hybrid Drive - into a commuter velomobile?

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velocoupe   100 µW

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Series Hybrid Drive - into a commuter velomobile?

Post by velocoupe » Jan 11 2021 3:12pm

In his article- Series Hybrid Drive: Advantages for Velomobiles-, Andreas Fuchs states that velos are ideal candidates for SHD Systems. The velo's slow acceleration and climbing is well suited because the pedals of the generator accelerate fast, gear changes are almost instantaneous, thus, maximizing optimal load time. Plus the aero and weight features of the velo complement the load-leveling capacity of the Electronic Drive providing a more physiologically constant advantage.
What do members think?
Is there sufficient merit to incorporating a SHD System instead of a Parallel System into a velo designed primarily as a practical urban commuter?

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by spinningmagnets » Jan 11 2021 3:52pm

When the proposed system has no components specified, it's easy for proponents to praise a system where the ideal motor does not exist.

Its also easy for detractors to insult the concept without any evidence.

I like a plug-in series hybrid for certain applications. A running velomobile would be interesting to see. In fact, I'd love to see a competition between two engineering universities to produce running prototypes, with the parts being paid for by a sponsor.

A good series hybrid design will always beat a poor parallel hybrid design, and vice versa. I would like to see a competition between two great designs put together by smart people who actually want their design to win.

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by Grantmac » Jan 11 2021 4:20pm

Isn't a bicycle drivetrain more efficient than any currently available generation and charging setup? Let alone adding the loses of running power exclusively through the electric motor.

I know I'm certainly curious if anyone can make it work.

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by amberwolf » Jan 11 2021 10:34pm

velocoupe wrote:
Jan 11 2021 3:12pm
Is there sufficient merit to incorporating a SHD System instead of a Parallel System into a velo designed primarily as a practical urban commuter?
You might want to read up on the Electrom by Tigcross, which AFAIK is of this type.
viewtopic.php?f=6&t=88612

There's not much left since his vids and pics are gone, but Lowracer built a really really nice SHD velo some years back.

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by velocoupe » Jan 12 2021 10:56pm

Hi amberwolf
Thank you very much for the link. I have viewed videos of the Electron on You tube, but the the info in this forum is far more helpful to my interests. I am trying to identify the most suitable electrical components as well as the design features which would apply to my tilting velo. Thanks again for guiding me to the Electron.

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by fechter » Jan 12 2021 11:03pm

Even using the best motor and generator out there, the losses in a series hybrid system are terrible compared to a regular chain drive. You could design with enough battery that you really don't need the pedal input and just use it to get exercise and slightly extend the range.

Another idea might be to use a differential between the pedal cranks and the chain ring and put the generator on the other leg of the differential. Like a Toyota Prius. This way at least most of the pedal power can go straight to the chain and avoid a bunch of losses yet still have the feature of being able to pedal at any rate (within limits).

To maximize human power efficiency, you really need to stick with a standard bicycle chain setup.
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Re: Series Hybrid Drive - into a commuter velomobile?

Post by velocoupe » Jan 12 2021 11:30pm

Hi Grantmac
You are correct, even Andreas Fuchs admits that the efficiency of a SHD cannot compete with a purely mechanical-drive bicycle. But he does claim that SHD is comparable (a few % lower) to peak efficiency of a Parallel Hybrid e-bike. Here are two examples of commercial Electronic drives. Bike2 Denmark into a upright bicycle,a cargo quad and a Sunrider velomobile. Plus the Podbike velo from Norway. They seem to work, but as spinningmagnets suggests, it would be interesting to see how Series-vs-Parallel) measure up. I have very limited experience in all things electrical. I joined this forum to improve my knowledge base hoping that some members have the knowledge and experience to help me fill in the blanks. For instance, What would be the actual percent lower efficiency of a SHD assuming as spinningmagnets says, both designs meet the best practice threshold.
Thank you both for replying to my topic.

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by amberwolf » Jan 13 2021 1:44am

velocoupe wrote:
Jan 12 2021 10:56pm
I have viewed videos of the Electron on You tube, but the the info in this forum is far more helpful to my interests.
It'll be easier to find if you use it's correct name, the Electrom. ;)

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by fechter » Jan 13 2021 9:19am

If your pedal generator has an efficiency of 90% and the motor has an efficiency of 90%, the overall will be 81%. In practice it's hard to find generators with higher than 90% efficiency (including any gearing). Most I've seen are much worse. If you spend a LOT of money you might be able to build something closer to 98% efficient. Something like a direct drive coreless generator. The more typical approach is to use a less efficient motor that's reasonably priced and put your money into more batteries.
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Re: Series Hybrid Drive - into a commuter velomobile?

Post by velocoupe » Jan 13 2021 5:17pm

Hi fechter.
Your reply is helpful. It's the quantitative data which will help me decide which route to go. Just wondering, would you consider the following claim credible? A SHD is just a few --? percent less efficient than a PHD. What conditions or qualifiers should I be looking at within this comparison?

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by amberwolf » Jan 13 2021 5:35pm

fechter wrote:
Jan 13 2021 9:19am
If your pedal generator has an efficiency of 90% and the motor has an efficiency of 90%, the overall will be 81%. In practice it's hard to find generators with higher than 90% efficiency (including any gearing).
Does this include the conversion electronics (DC-DC out of the generator to the battery, and controller out of the battery to the motor)? If not, it'll make the efficiency even worse. :(

A single-stage chaindrive by itself, from pedals to ground, can be 98% efficient, so that's pretty hard to beat.

I don't know off the top of my head what parallel hybrid efficiencies might be possible; it depends on exactly how they're setup, and where on the efficiency curve you're using it (because in the motor system, there is a peak efficiency point and anywhere else its' less efficient than that). Assuming the pedal drive is the above type, and it's geared so it can contribute significant power thru the entire speed range, then that part's efficiency would raise the total system efficiency depending on the proportion of pedal power to motor power. A high motor power system would be less efficient than a low power motor system, because the proportion of efficient pedal power is higher for the latter. I'm not good at making formulas, but the efficiency should be a simple ratio between the two. If you had a 90% efficient motor system of 250w, and a 98% efficient pedal system of about 100w (typical human output), then it would be 90% of 250w : 98% of 100w, or 225w + 98w at 90% * 98% efficency . Total of 323w output, at 88.2% efficiency. I think. Not sure if that's the right math, but you get the idea, I hope.

Also, your power outputs *add* like this, where they do not in the serial system. (you only get 225w output using the same stuff in serial setup, vs 323w).


But a serial hybrid each stage of inefficency multiplies the total system inefficiency, and as you see by Fechter's example, it's significantly less. Assuming his example includes the electronics / conversions, then that's a difference of 7.2%, which means with the same motor setup of 250w, and 100w of pedal power into the generator, then of that total 350w, 0.072 * 350 = 25.2watts of that is wasted as heat.

Sorry about the wandering thoughts above; I've been typing this over the last hour or so while the dogs have been (successfully) trying to get my attention instead. :)

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by velocoupe » Jan 14 2021 5:09pm

Thanks amberwolf. So a 323w output in a parallel system results in approx. 88% efficiency-vs-81% (fetcher's calculation) and possibly 7.2% less for the series. This is the quantitative stuff I've been looking for. Thanks.
Would it be correct to say that the Electrom's blend of a direct chain drive at slower speeds for accelerating and climbing combined with generator assist for all speeds (no gear box- derailleurs)is a good compromise for reducing the inefficiency of the SH at slower speeds while benefiting from an auto-like transmission. It's the gearless feature which I find appealing for my velomobile. Or are there additional variables and calculations which I should be looking at in that design?

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by amberwolf » Jan 14 2021 6:09pm

velocoupe wrote:
Jan 14 2021 5:09pm
Thanks amberwolf. So a 323w output in a parallel system results in approx. 88% efficiency-vs-81% (fetcher's calculation) and possibly 7.2% less for the series.
Assuming I did the math right. :oops: No guarantees on that. ;)
But...the main thing to me is, PHD pedal + motor means you get more power to the ground out of exactly the same motor/controller setup vs SHD.

To get the SHD to give the same power output, you'd need a bigger controller, possibly bigger motor, possibly heftier battery (has to support higher current), and *then* add the weight of the pedal-powered generator and DC-DC/charger.

SHD's primary advantage, to me, is that in a trike or quad style setup (vs a bike where you can't really do this without yet more stuff to hold you upright) you could sit there continuing to pedal and recharging the system anytime you were stopped, both keeping your muscles active at whatever level you chose even though your'e stopped (say, waiting for traffic to clear a road or an intersection so you can cross, which can take minutes or more in some places), and could have exactly the same load on your legs all the time (if the charger/DC-DC is setup to always place the same load on the generator), vs a changing load (even with gear changes) on different terrain or wind conditions, etc. that you would have with PHD in the same conditions.

The other potential advantage, depending on the drivetrain layout vs the bike or trike/etc design, is SHD eliminates any (often long, in a velo) chainline from pedals to wheels, so there is potential mechanical design simplification. But sometimes a simpler shorter chainline can be achieved by routing to a closer wheel, depending on usage, etc.

If none of that is a benefit to you, then the PHD is a "better" option.
Would it be correct to say that the Electrom's blend of a direct chain drive at slower speeds for accelerating and climbing combined with generator assist for all speeds (no gear box- derailleurs)is a good compromise for reducing the inefficiency of the SH at slower speeds while benefiting from an auto-like transmission. It's the gearless feature which I find appealing for my velomobile. Or are there additional variables and calculations which I should be looking at in that design?
Don't know. Best recommendation is to read the Electrom's threads (there are several over time) where Tigcross talks about some of the design decisions, etc. Or ask in one of the threads, if it isn't already in there.


If by "gearless" you mean that you wouldn't have to shift gears for the pedal drivetrain, you can get or make automatic shifting systems for derailers or IGHs. There is at least one thread developing one here on ES.


If instead you mean saving weight or complexity by leaving those out...you lose that savings by adding the generator/charger/DC-DC system. ;)

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by velocoupe » Jan 15 2021 5:56pm

Hi amberwolf.
You successfully identified my reasons for inquiring into the SHD; recharging at stops, constant cadence/loads, not having to shift gears on the pedal-chain system, simplify the drive-train layout to the rear swingarms of my tilting delta velo.
I am looking at three options. Plan A -(if it can be justified?) is to entirely remove the existing chains an derailleurs which drive the right rear wheel and install a single sided all axle hub motor on the left rear wheel, and install a dedicated pedal generator from Bike2 Denmark with their controller configured to work with the Grin motor. (most simple but costly in $$$ and Watts) Plan 2 is to retain the pedal drive and just add the Grin components in parallel. Plan C is to determine if the Electom's drive system is more suitable since his chain drive requires no gear shifting.
I will re-read "Introduction to the Electrom" for the third time and also ask in one of the threads. I will also look for the discussion on ES regarding automatic shifting systems for derailleurs. Thanks for the suggestions.

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by amberwolf » Jan 16 2021 12:26am

velocoupe wrote:
Jan 15 2021 5:56pm
Plan C is to determine if the Electom's drive system is more suitable since his chain drive requires no gear shifting.
Is that "requires" no gear shifting, or "allows for" no gear shifting? The two are different, and I don't know which is true of the Electrom's system. ;)

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by velocoupe » Jan 17 2021 5:13pm

Hi amberwolf.
My take on Tig Cross's description of the Electrom is the chain to the rear wheel is set to an optimum low gear (can't change that ) and there is no gearing to change on the generator side because there is no need for gears.

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by fechter » Jan 17 2021 11:07pm

There are a lot of trade-offs in the various design approaches. The least expensive and simplest systems won't be the most efficient, but possibly efficient enough to meet your expectations.

I've always kind of liked the series hybrid concept, but every one I've seen built so far hasn't performed very well. If you can make the generator part really efficient, that's going to be the real key. Motor parts are off the shelf and all kinds are available. The generator only has to handle how much power your legs can put out. In my case, that wouldn't be very much. Lance Armstrong is something like 600w. To make it direct drive and avoid gearing losses, the rotor would need to be very large in diameter, but this might not be a big problem on a velo.
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Re: Series Hybrid Drive - into a commuter velomobile?

Post by amberwolf » Jan 17 2021 11:13pm

Ok, so it means it "allows" no gear shifting. ;)

If you found that you did need to shift pedal gears at the rear wheel, you can design yours so that is possible (if you require a single-position chainline rather than a derailer, you can do it using an IGH in the rear wheel, or as a jackshaft inline with the pedal chainline to the rear wheel)

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by Hillhater » Jan 18 2021 6:53pm

velocoupe wrote:
Jan 17 2021 5:13pm
Hi amberwolf.
My take on Tig Cross's description of the Electrom is the chain to the rear wheel is set to an optimum low gear (can't change that ) and there is no gearing to change on the generator side because there is no need for gears.
If there is no or fixed gearing between the motor and the wheel, why could it not be a suitably chosen hub motor,
and eliminate the weight and efficiency loss of the chain drive + sprockets ?
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Re: Series Hybrid Drive - into a commuter velomobile?

Post by amberwolf » Jan 18 2021 9:48pm

That's what this thread is all about--whether to do a serial hybrid (like you describe) or a parallel hybrid (with the chain). Each has it's advantages and disadvantages...as discussed above.

Tigcross's Electrom is *both*, depending on speed / mode. :)

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Re: Series Hybrid Drive - into a commuter velomobile?

Post by Hillhater » Jan 18 2021 11:24pm

Yes, i was confused by your reference to the possibility of using an IGH for gearing...
Obviously you were refering to a different design.
But whilst i see the benefits of the recumbent layout,..The complex hybrid drive seems to have no advantage over a conventional “parallel hybrid” Ebike drive.
Tigcross states that the “rider” input of 150 W is not significant on the 2000w system capability, and adding little to the 1440Wh battery capacity, verified by the typical 20-30 Wh/km consumption.
For me, a simpler drive train, (mid drive ?), with the complexity, cost and weight of the generation system swapped for more battery capacity, would seem a better option.
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Re: Series Hybrid Drive - into a commuter velomobile?

Post by fechter » Jan 19 2021 9:13am

150W would be about what I could do on a good day. From there it's not hard to do the math or use the Grin simulator to see what kind of range/speed you'll get.

One other consideration (a pretty important one to me), is if your electric system fails, a chain drive will offer a human powered backup mode. More than once I've had to do the "pedal of shame" after something failed in the electric drive system.
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Re: Series Hybrid Drive - into a commuter velomobile?

Post by Hillhater » Jan 19 2021 5:36pm

There is no doubt that the hybrid generator will give you extra range ( approx 20-25% if continuous pedaling at 150 W ), but so would similar pedaling input on a normal parallel drive Ebike .
Whilst 150W is typical for a healthy adult for an hour or so, it is generally accepted that 75W is about the average for a sustained period. Once you factor in the efficiency of generator, inverter, battery storage , controller, motor etc... i suspect it is closer to 50 W of power at the wheel from the pedal generator.
And if you prefer an easier ride the cost of that generator system will buy you more than the equivalent extra battery to do the same job.
And, as you say, if you run out of power etc, you can pedal normally.
So where is the benefit of this “Generator hybrid” system ?.
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Re: Series Hybrid Drive - into a commuter velomobile?

Post by amberwolf » Jan 20 2021 1:34am

The main place I myself see the potential benefit is that if you are on a trike or quad (where you don't have to balance at a stop), and you will be stopped for significant lengths of time during a ride but must remain on the trike/quad, you can sit there continuing to pedal and generate power and continue to exercise at the same rate, keeping up your heart rate/etc (if this is a goal for you).

A second potential benefit in some cases is that you also can have a completely constant load on your pedals regardless of any ride conditions (if the generator is setup to do that), which for me would be a lot easier on my joints/etc. than a constantly-varying load and having to shift gears to alleviate too-high loads, or being unable to load the pedals at all because you run out of gearing (fast downhill stretch, etc).

However, as you note, the money/weight in a generator system is very likely to buy enough battery to completely replace the power that would have been generated above. The other potential benefit might be achievable some other way, like with an autoshifting Nuvinci (or other CVT) with sufficient gearing range for you.

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