The FORCE dyno

Endless Sphere

http://endless-sphere.com/forums/viewtopic.php?f=30&t=47930

Conclusive proof gearboxes are awesome.

...I don't read Endless Sphere much anymore (I was one of the original posters there) so it was interesting to check in on them.

Basically they are "still" arguing the same question:

"Are gears needed?"

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LiveForPhysics (Luke) is still arguing (correctly) that Torque is all about Current. Motor rpm really only creates things like friction and iron core losses, so if you really want to accelerate like a dragster you just need a bigger motor.

This is "true" if you are thinking in a narrow sort of way.

Thud provides the upper midwest humor. :)

...and there are those with the classic counter argument that if you are "forced" by something like human created laws to use a smaller motor that as a practical matter gears are helpful.

No one "so far" has grasped the "Power = Force * Velocity" significance.

What really matters for ebikes (in my opinion) is the Force portion of the overall equation.

Force is related to Torque and that comes from Current.

What we want for ebikes generally is single speed and "constant current" power.

"Constant Current" is the best way to give ebikes an identity separate from motorcycles.

0.1G of acceleration for a 250 lb rider is 25lbs of Force.

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If people only knew how good the "constant current" feels they would understand. It doesn't feel dramatic (it's not violent) but it shouldn't be because... well... it's a bicycle silly !!!
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Hills are a Problem

What does a hill do?

If you have a given acceleration (say 0.1g) then as the hill becomes steeper and steeper you are subtracting from that acceleration by an amount equal to the "rise over the run".

Force based racing attempts to "reintroduce" the need for pedaling and on flat land everything is perfect, but once you introduce a steep enough hill your ebike becomes not very effective.

It's a tough problem... allow "constant power" and you make pedaling pointless on flat land, but if you use "constant force" which is great on flat land but disappointing on hills.

Seems that the "solution" is to stick with "constant force", but adjust the level to suit the track. If the track has a lot of hills you would allow a higher Force.

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...already getting the first of the fatigue/stress related problems.

There is a crack in the clipon connector.

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Long day...

Rode regular bike 10 miles.

Drove across town to a guy who welded the cracked clipon part $18. (I put my own welder into storage last week)

Rode the ebike three times for 10 miles each. (serious lean angle stuff)

Finally got an old computer setup to reconfigure the controller settings.

Tomorrow the new settings are:

Overvoltage (maxed out) at 45 volts.

Undervoltage 32 volts.

Motor Current Limit 43 amps. (translates to 25 lbs of Force)

...hopefully this will be ideal.

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Going Into Storage

This project was started way back in 2007.

It's great to have gotten it running, but I bought an undersized Kelly Controller that seems to be faltering already. The specification suggests a maximum of 40 amps continuous and I've been running 50 amps and on regen the voltage spikes above the controllers limits too. Now the controller cuts out all the time. What's worse is the PC to USB interface has failed completely. I no longer get any power in the USB and the RS232 cable was getting warm while I was trying to use it. (so something got fried). In a sense the controller is "bricked". The ebike only runs when the battery voltage is on the low side. A full battery almost instantly triggers overheating.

Ideally I need to upgrade to:

http://kellycontroller.com/kds72200200a24v-72v-mini-brushed-controller-p-288.html

KDS72200,200A,24V-72V, Mini Brushed Controller

Peak Current, 1 minute: 200A

Continuous current: 80A

$150

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Other options:

Complete the RC motor upgrade that I gave up on and then switch to a brushless controller.

Go back to the low tech chinese controllers that are durable, but lack programmability.

Search for other controllers.

Increase voltage to make the bike capable of higher speeds. (this becomes possible with the 72 volt upgraded controller)

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For now I'm satisfied with taking a break for a while.
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Good News...

After spending a little over a year in Nevada I've decided it's not for me and am in the process of moving back to the midwest to Wisconsin.

I have a friend out there already and he's helped me find a place to live that is affordable and has a workshop.

So the project will continue and if there are people in the upper midwest that might want to get involved in this sort of thing we should get together.

Wisconsin has Germanfests, Oktoberfests, and just about every festival a man could want and the people are (known by experience and scientific fact) extroverted and agreeable, but NOT necessarily very open. California is the state that is most open, but they score low in the sociable areas.

So let's get some "nice people" in the upper midwest for some track time some day.

Gemütlichkeit might actually be the key to getting the sport going.

http://en.m.wikipedia.org/wiki/Gem%C3%BCtlichkeit

California prides itself in being "exceptional" and you might think that this would lead to a better place to begin this type of sport, but this isn't motorcycle racing where unlimited or excessive power seems to be a good idea. As a sport rooted in cycling the task is figuring out the right sort of restriction to make the sport make sense. For that you need "rule following" cheerful and agreeable people and you find that in the midwest.

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http://www.recumbents.com/wisil/seanarticle1.htm

The future of Racing HPV's

An article by Sean Costin

I have been giving some thought to the future of Racing HPV's and have come up with some ideas on what we might see in the next Millennia. Any analysis of the future should focus on the current limitations. These are the problems that HPV designers are hungriest to solve.

These are the biggest problems:

1. High speed handling and cornering
2. Drive train inefficiency
3. Aerodynamic efficiency.

Races can be won and lost in the turns. A bike that can turn at a faster speed has a tremendous advantage over a competitor if a course has tight turns at the end of a fast straightaway or a downhill, such as the ones in Mooresville and UW Parkside. Cornering can become very treacherous at speeds in excess of 30 MPH especially when bumps are present that can unweight the tire, causing a complete loss of traction that will put a rider down in an instant.

I actually discussed some of the ideas about recumbent racing with the guys at the Portland International Raceway many years ago. The core issue that limits recumbents is the low center of gravity. While the fall is less with a lower center of gravity it also comes much quicker. On a Go Kart track where slipping and sliding is to be expected the recumbent will crash with the first slide.

Upright ebikes actually make more sense... though the aerodynamics of recumbents are much better.

Recumbents are best for speed records in straight lines, not on curves.

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I would be curious to see a link to a Go Kart track race with recumbents. Didn't see it.

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Well, I'm definitely looking forward to learn about the tracks in Wisconsin.

I know Go Kart tracks are pretty popular there.

At the moment I'm still in California, so I'm still over 2000 miles away.

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My point is still that recumbents aren't particularly good at controlling a slide when you are on the edge of traction. With a road racer styled upright bike you can let the tires slide a little and feel pretty relaxed about it. It's all about the physics of high verses low centers of gravity. High is better because the rotational axis allows for a longer torque vector for rotation. It's like having a bigger hammer, you get better leverage. This is why you don't see motorcycle road racers using recumbent designs because they are less able to slide successfully.

A good motorcycle road racer can slide the tires at will just about anyplace.

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It all comes down to what the "contest" of racing is about.

Is it low power and top speed due to better aerodynamics? (recumbents are good at this)

Or is the motor there to give higher top speeds and the "skill" is in sliding through tight turns?

When and where should pedaling be done?

...the answer to the last question is that pedaling is only done below 20 mph and the motor does the rest, at least that's how I'm seeing it evolve. Force is a better metric than Power.

http://en.m.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics#section_3

Basically a bicycle can be seen as an "inverted pendulem".

Acceleration of the mass (rider + bike) is caused by contact of the tire with the ground.

The shorter the distance between the center of mass and the ground will translate into a more rapid rotation about the axis for a given "slip" of the tire.

The result is less time to react when the tires slide.

For this reason if the sport is run on a Go Kart track where being on the edge of traction is a "majority concern" it makes sense to choose the higher center of gravity upright ebike even though it's aerodynamically inferior to the recumbent.

In my youtube video you can see that 30 mph combined with a typical corner in a regular street produces a lean angle that barely even makes the rider concerned. You need to either have tighter turns (like on a Go Kart track) or higher speeds to stress the ebike more. So far I've pushed the ebike as hard as I can and haven't gotten the tires to even break loose. It turns really well and seems to like more lean.

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Constant Force has only the aerodynamic drag as it's upper limit.

So there is no "power limit" so to speak.

On my ebike now it's producing something like 1600 watts or about 2hp at full speed, but very little power at low speed.

Basically it's a totally different approach to the problem.

You might have something like:

Power = Force * Velocity

@10 mph ---> 500 watts = 25lbs * 10mph

@20 mph ---> 1000 watts = 25lbs * 20mph

@30 mph ---> 1500 watts = 25lbs * 30mph

@40 mph ---> 2000 watts = 25lbs * 40mph

...the math gets messy sometimes, but you get the idea.

Power needed for top speed becomes a "non-issue", but ACCELERATION is constant and small.

Acceleration is basically intended to be limited to 0.1g.

It's a fresh new take on things. :)

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30 mph was a sort of purposeful "self restriction" so that I wouldn't run into troubles with the law.

On the racetrack if you just allow more top speed then the traction issue goes up.

In past ebike projects I've gotten into the 50-60 mph range.

The main point is the Force mandates pedaling at lower speeds because power is low. But at higher speed there is no shortage of power.

Power = Force * Velocity

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And it's also important to understand that the "Force Level" to be permitted in the future is not yet cast in stone. I'm still experimenting with just how much is appropriate and there might be adjustments to compensate for things like rider weight.

But "Force is the better metric" for ebike racing because it makes people pedal at slow speeds. (something excessive power does not)

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From the legality standpoint Force makes things easier because if you sell something like this at a legal 20 mph top speed and a peak power of 1hp, then if you double the voltage you will go 40 mph and make 2hp. Heat is largely the SAME because constant Force means constant motor current. This last point is very attractive.
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