Comments on: Batteries, part two or Better living through sewer pipe

By: Todd

Todd — Sun, 06 Aug 2006 17:01:03 +0000

Victor, I think 300 or so watt hours is the minimum worthwhile amount of battery to carry on a vehicle meant to complement plain bicycles, so I’d find the water bottle format too restrictive with today’s technology. Soon I’ll be evaluating a pack meant to mount to the water bottle bosses, though. Minimum nominal frame size for that mount point is 21″. I suppose I’ll just carry it in the cargo area instead of put that amount of weight in that part of the bike.

By: Victor

Victor — Sat, 05 Aug 2006 17:39:02 +0000

Hi Todd, congrats on your stokemonkey coming to fruition. The idea of making a battery connect and/or look like a water bottle seems like the best way to do it. (my epiphany, lol) I’ts good to see you have batteries for sale. Too bad you have to make them yourself. I really like your enclosures. And they look almost like water bottles! Of course I have no idea what the actual size of water bottles are for bicycles; I only know that my bike has screw holes for 2 bottles. And alsoI have bolted an aluminum frame to hold 18lbs of sla in there, attached only be 2 screws into the lower bottle mount. And duct tape to keep it steady. After many miles of wheelies and smashing road crevaces at 30mph, the battery mount ifs fine. (my spokes aren’t). When I get the appropiate lithium, I want to make a water bottle battery. Then this will fit just about any bike made? Do you think this is a viable route to take? If it is, then please (anyone) please steal my idea and make one, ’cause I’ll buy it. (It also must cost less than $300 per 5ah 36v bottle.)

By: Eric

Eric — Wed, 19 Jul 2006 18:07:36 +0000

Also, one other interesting “non-intuitive” fact about batteries and motor size is that while the range on the flat will go down with a larger motor because the bike will go faster (and thus push more wind) it actually has no effect on slow uphills. When you run the calculation for a 500 watt motor verses a 750 watt motor on the hills it produces the same range. Interesting huh? Within limits the motor size is not as important as one might think. (it’s okay to use a larger motor… but since you are tempted to push more wind it hurts the range, but it’s not due to losses that one couldn’t control if disciplined)

By: Eric

Eric — Wed, 19 Jul 2006 17:50:52 +0000

The amount of batteries needed to have won todays difficult stage in the Tour De France?

Using 2 of the Valence 12V 130Ah 41lb Lithium Batteries we get a calculated full power time of 6 hours and a distance on the flat of 250 miles using a 500 watt motor. On a 10% grade you get a maximum of 58 miles. So you get:

(10% grade) sin(5) * 58 miles * 5280 ft/mile = 26,500 ft

Which is about the amount of time, distance and climb that was needed for this stage. It’s definitely possible.

For a typical 1.2V 10Ah Lithium Cell we would need to have:

1.2V * 10 = 12V
12V * 2 = 24V
10Ah * 13 = 130Ah

So we would need 10 * 2 * 13 = 260 Cells!

At a typical price of $5 per cell we get $1300. (not bad)

By: Eric

Eric — Tue, 18 Jul 2006 22:09:11 +0000

And I’ll add that on the Stokemonkey the weight is low, but also in the rear. This is good. The problem positions is placing the battery low and forward. Imagine a “pivot” line stretching from the center of your rear wheel forward to the top of your front fork. As long as you stay near this “pivot” you are okay. Having the batteries straddle the rear wheel is correct. Above the rear wheel is too high. (many have the batteries placed like it were a bike rack)

By: Eric

Eric — Tue, 18 Jul 2006 21:50:29 +0000

Another subject is battery placement. Long, long ago I did a little “pit work” out at the old Laguna Seca Raceway for a guy racing in the Formula 2 (250cc two stroke) class. At the time there was a theory that placing the gas tank below the engine would lower the center of gravity of the bike. I was actually working on a test gas tank until one of the guys doing it already crashed badly and people realized that the theory was wrong. Apparently the way a bicycle/motorcycle steers is not as people theorized, the actual “pivot” point is up pretty high… about three quarters of the height of the wheel and basically the further from the “pivot point” you place any weight the worse the weight effect it produces. (it makes the weight “seem” heavier) These scooters that place the batteries very low are actually producing a very poor handling machine. The ideal location for batteries is hanging from the top tube of your bike. (or near there) This is a problem, however, because that’s exactly where your legs need room to pedal. So from a “performance” standpoint the batteries need to be between your legs in the middle of the bike. This is a bonus however when it comes to aerodynamics. Since the batteries are best placed high (near where the aerodynamic “pocket” exists) you are effectively “killing two birds with one stone”. You end up with the ideal handling and low aerodynamics. Placing the battery in the back in the “middle/forward position” is a good location since your body weight is forward to balance the battery.

By: Eric

Eric — Tue, 18 Jul 2006 21:26:31 +0000

Well, you can always downshift at the right moment to avoid those big spikes. It would be important to know how to ride the bike well because you could ride it in the wrong gear all the time and never know it. This is a very good point actually and one that I’ve discussed with the “other Todd”. (Todd Kollin at Electric Motorsports) One idea I had was to do like the Indy Car steering wheel LED lights for the RPM. If you look on those steering wheels they have three LED’s that light up when you go below the powerband and another three LED’s when you go above the powerband. Such a system could let you know when you are getting “peak” performance out of your electric motor. (you would know when to shift up and when to shift down)

I was just working on the aerodynamic stuff and this is what I came up with…

Aerodynamic drag can be calculated with this equation:

Drag = 1/2 * (Air Density) * (Velocity) * (Velocity) * (Drag Coefficient) * (Frontal Area)

There’s nothing you can do about “Velocity” because it’s the central factor and it’s squared too. The “Drag Coefficient” you can improve with fairings… but that shows diminishing returns. It’s the “Frontal Area” where a compact “Road Racer” could significantly out perform a pedaling bike. Compact the legs up into a “tuck” position like the motorcycle road racers do and you can cut the “Frontal Area” about in half. Look at the frontal view of a bicycle and half of the frontal area will be the legs. Legs that move also create all kinds of eddy currents… it’s an aerodynamic nightmare… and that means lost power… wasted battery energy.

By: Todd

Todd — Tue, 18 Jul 2006 20:59:52 +0000

Yes, diversity — I wasn’t trying to dump on your concept, just differentiate mine. Another advantage of driven pedals is simply to assure that the gears will be used more assiduously than without; use the human lizard brain instead of an automatic transmission. Also, even with variable gearing, certain moments will call for hard pedaling to avoid big amp spikes. You’d need a much more powerful/robust electric drive to make pedaling truly irrelevant; I’d argue that you get a big efficiency benefit right there, in not having to upsize the electric drive with associated weight gain. Also, yes pedaling is fun, or endorphins are, at least. I’d sure rather pedal than dance, or ski, or jog, or climb rocks, or swim, or all sorts of other physical activities that people undertake for pleasure.

By: Eric

Eric — Tue, 18 Jul 2006 20:31:17 +0000

One solid advantage of keeping the pedals around is that you can run out of power and still get home. The inability to pedal means that you need to keep tabs on your trip. It makes the machine good for short “sport” rides, but not good if the distance is unknown. My idea is for someone that wants to take a quick ride through their favorite nearby backroad and then before the hour is up park it in the garage and do something else. It’s the “quick fun ride” idea, not the marathon. (of course with Lithium and a range of 150+ miles you could go plenty far enough)

By: Eric

Eric — Tue, 18 Jul 2006 20:15:09 +0000

There will always be many categories. I’m seeking to answer a different question than most:

“How can I (as a human) get from point A to point B with the minimal amount of energy, lowest cost and have fun while I do it?”

Many of these Electric Vehicles weigh tons, like most regular cars do. This is a very inefficient way to use energy to transport your body even if you can “charge it” so that you can claim to be “green”. In the “big picture” of things, people like “sport” (thus the “Road Racer” styling, like the GP motorcycle) and they like not to spend much money. (look at WalMart) So I’m simply trying to create something that fits that niche of people who like to ride for pleasure, but who are also a little concerned about the idea of a pleasure ride that wastes gasoline. “Fun riding without guilt” might be the slogan.

If someone wants exercise they can ride their bicycle.

Unless it can be proven that pedaling increases efficiency of the overall system compared to “other options”, then it doesn’t contribute to the goal. I’ll add that my first sketches involved something that looked a lot like Stokemonkey in the drivetrain department, I was going to combine pedaling with the motor as you do. It STILL a great idea to use gears… that is completely missed even by the racing electric motorcycle crowd. Battery effeciency is closely tied to engine RPM (I’ve studied all the performance graphs) so you are 100% on track with that idea.

Diversity is okay… :)