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Old 11-23-2012, 06:29 PM   #1 (permalink)
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Electric Motorcycle moonshot idea.

Are there any instant mpg gauges for motorcycles?

I'd like to compare mpg at mph curves for 125-250cc motorcycles. Specifically, i want to be able to calculate the cost effectiveness of adding a hybrid system. What benefit a motorcycle would have from a low speed hybrid system, so that i'm only averaging combustion engine mpg at cruising speeds.

The second purpose is to try to estimate how high an mpg i could potentially get while cruising at 55-65mph with a continuous long range low power (1/2 total hp of cruising speed?) electric assist to the gas engine. Also how small a displacement engine could i get away with with such a system.

This would then indicate what battery capacity has the most impact for price and range. I suspect a small 3kwh. The expandable lithium battery bay, 3-10kwh would allow me to add more kwh over time.

The 5 year plan is to have a 90-100% faired in vehicle that can potentially get 200+mpg (maybe significantly more) with the benefit of plugging in before the battery is empty, and 150+mpg crossing the country at 65mph. The electric motor would be able to run independent of the gas engine either by front wheel electric drive (if safe), or by the ability to declutch from the engine.

Anyways, that is my moonshot idea. I won't be constructing anything in 2-3 years so don't get any ideas. I need to learn many things about welding, fiberglass, and EV conversions. And i don't have the necessity of requiring such a high mpg bike, or the financial motivation as of yet. I expect in 5 years that Lithium prices will drop, and gas prices will rise. Making the project even more financially viable.

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Old 11-23-2012, 06:44 PM   #2 (permalink)
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Isn't motorbike gearing well suited for low speed since it's so short? From what I understand you can just go into the top gear really early and roll along at 30mph getting insane mpg? Highway on the other hand runs the short geared engine up to very high rpm which is extremely inefficient.
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Old 11-23-2012, 07:13 PM   #3 (permalink)
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Thank you, your right that a motorcycle will consume far less fuel accelerating to speed than a 2,000lbs car. Maybe that isn't where the most improvement could be had?

I hadn't thought about how having an electric assist not only throttles the engine less, but i could then get away with insanely high gearing and maybe even see better than expected results. I'm thinking a final gear that would bring a normal motorcycle to a crawl. Gearing is the other half of mpg gains from Aero as they say.

My inspiration is a cross between the 200mpg 125cc honda innova, and the 470mpg winners of the vetter challenge decades ago.
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Old 11-23-2012, 07:20 PM   #4 (permalink)
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Well, if you can measure the fuel consumption paired with speed you would have something there. I think they make fuel injected bikes as well as flow meters. Maybe you can rig something up?

At the least do what mythbusters does. Make a fuel cell, weigh it, drive x number of miles at desired speed, then weigh whats left and repeat at different speeds.
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Old 11-24-2012, 06:59 AM   #5 (permalink)
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There isn't much room in the chassis of a two wheeler for all of those components. Maybe if you used a hub motor.
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Your gas engine will need to make at least 100% of your power at highway cruise. 15 hp?
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Hybrids don't really improve highway economy. They just improve the acceleration of a really efficiently undersized gas engine and provide some regen braking around town.
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Old 11-24-2012, 08:54 PM   #6 (permalink)
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The motorcycle would be extended for aerodynamic and stability reasons. Taking the the example of the 200mpg honda innova; I believe a motorcycle can achieve 33.5-50wh/mi in EV mode through a complete aerodynamic fairing and the small frontal area of a bike. This is about 680-1,000mpge, 680mpge being my conservative goal (which is phenomenal compared to cars). For 100 miles of range, that would require a 3.7-5 kwh battery. I've been told "using standard lithium technology would only be 3.7kWh, or about 82 lbs, and would measure about 5 x 18 x 25 inches, thus easily fitting under the seat for example." Such a small pack would be relatively cheap, don't know how much but south of $2,000. To start, i could get away with a really cheap 2.5 kwh battery for 50 miles. To compare, this is plugin car range, not prius hybrid territory.

My theory is that diluting a 100 mile EV range over 300 miles constantly assisting the gas engine is better than driving 100miles in ev mode, then 200miles on gas only. At a 100mpg gas engine for the second example, i would average 150miles for every gallon of fossil fuel consumption. But how high an mpg could i get cruising at 65mph by throttling back the engine from a 15hp cruise to 1/3 (10hp gas 5 hp electric) or 1/2 (7.5hp gas 7.5hp electric)? I know in my car a little less throttle to where the car slowly looses speed will jump the instant mpg gauge a lot high than what i get maintaining speed.

I'd like to try to extrapolate a graph of how a motorcycle's gas engine gains mpg by throttling back the engine in percentages, while still maintaining the same speed. Would it be linear? Is there a sweet spot in the curve where mpg skyrockets?

I think in constant assist mode, the electric motor would also be able to cherry pick ideal conditions to get the best mileage. Take the VW XL1 for example, the sum of its short plug in range and the mpg it gets on diesel will never be able to add up to the 300+mpg it's stated to get. Something else must be happening when they run in combination.
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Last edited by sheepdog 44; 11-24-2012 at 09:05 PM..
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Old 11-30-2012, 06:02 AM   #7 (permalink)
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I see where you are coming from, stretch it to be able to fit passengers and cargo in a low frontal area, keeping the vehicle safe in traffic on the other hand would be the difficult part. A low vehicle means lower cd and frontal area, however your visibility goes down with area. Shell designed a vehicle that could get 12000 miles to the gallon, however if it drove down I-35 it would get smashed because nobody would be able to see it.

Have you given any thought to the boxfish shape to be able to incorporate more space into a streamlined shape? Making you more visible?
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Old 11-30-2012, 06:43 AM   #8 (permalink)
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Quote:
Originally Posted by sheepdog 44 View Post
Is there a sweet spot in the curve where mpg skyrockets?
Yes. The opposite of what you are thinking. 90% load at the rpm of the first torque peak. 50% percent load is never more efficient. That's why we Pulse n Glide.
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The best streamlined electric bikes are still over 100 Wh/ mile at 100 kph. Some electric bicycles can get to 30 Wh/ mile but at a much lower speed of 30 kph.
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Old 11-30-2012, 07:57 AM   #9 (permalink)
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What about going with a vintage vacuum gauge as a way to interpret engine activity into fuel efficiency?
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Old 11-30-2012, 09:41 AM   #10 (permalink)
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A vacuum guge would work fine, but you might have to add a small reservoir to dampen the oscillations in the gauge at lower RPM. Most bikes with vacuum petcocks already have a fitting in the intake manifold that you could use for your vacuum source. My 87 Rebel 450 has one as well as the Vulcan 500. A tee off the petcock hose would give you a vacuum source without any other modification.

On a Rebel 250 the petcock is not vacuum operated, so you would have to drill and tap the maifold for a vacuum fitting. The Rebel 250 uses a single carb for both cylinders, so it would provide a more steady vacuum source, but might still need a small reservoir to prevent gauge flutter at lower speeds. Try it both ways and see whish one works well enough for your preference.

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Mech

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