Mounting your battery, Center of Gravity.

[John in CR]

Then during turn the centrifugal force and the traction of tires reach an equilibrium with gravity to stop you from falling all the way over.

bingo!

(challenge to safe: let's see if safe can draw a PROPER 2-d vector diagram of this.)

My prediction- subject change again. That or we may get to see his ideal battery placement image again.

 

[Dee Jay]

Seriously though... are you unable to make the intellectual leap to a vector for traction?

nice try safe.
but your attempt to manipulate yourself into a teacher position is failing when you can't even get the vector diagram correct.

you see safe, when you make condenscending remarks like this:
"(are you just being a "pain in the ass" or are you really confused.... come on.... be honest)"
i end up just laughing cuz i know something that you don't know.
you want me to be confused, don'tcha?
tell me, when you make condenscending remarks like this, does it give your ego an erection or something of the sort?
(there, how's that for being a pain in the ass)



hint: you talk quite a bit about one of newtons laws... for every action, there is a reaction....

so why not start including the reaction vectors in your diagrams to make them more complete?

is wikipedia your "bible?"
you reference it so much so why not look up friction forces as applied to rotation and centrifugal forces and start mapping these force vectors into your oversimplified and incomplete diagram(s).

All that . . .

Yeah, off with the lab coats. Stop trying to dazzle us with numbers and charts. Give us some real life examples. :lol:

J

 

[John in CR]

All that . . .

Yeah, off with the lab coats. Stop trying to dazzle us with numbers and charts. Give us some real life examples. :lol:

J

But his real life example is that he couldn't figure out the right vector quick enough to squeeze by a truck truck hogging the road a bit and ended up in a ditch instead of staying on the road.

John

 

[safe]

Orthographic Drawing

...

...

Before we can get to calculations of simple bodies in motion (very much within the realm of physics we can be certain about) we need to have an understanding of what vectors are, how they are used, and the coordinate system that they will be displayed upon.

We live in an age where three dimensional drawings are commonplace. But early on engineers discovered that three dimensions can be broken down into two dimensions taken from different points of view. So it's possible to represent a three dimensional idea using only two dimensions and multiple views.

Will anyone here have any problems with this idea of orthographic drawings?

I've probably drawn hundreds of these orthographic drawings in my lifetime, so they are second nature to me, but if there are any people who are new to them let's hear questions now.

http://en.wikipedia.org/wiki/Orthographic_projection

 

[safe]

The High Wheel Bicycle

We are actually going to take a trip down memory lane because one of the first bicycles actually is an example that is easiest to start with. The "High Wheel Bicycle" had the mass of the bike and rider centered above the front wheel. From a mathematical perspective this is an easy place to start.

The problem with these machines (as we will see later) is that they tended to not have enough weight in the rear to allow for braking without flipping over the front of the bike.

...it was because of this that later designs sought to find a new compromise.

 

[safe]

Orthographic Drawing of High Wheel Bike

I'm still building the foundations for the math. This is the drawing of the High Wheel Bike represented as a Center of Gravity (CG) and it's shown in three two dimensional views, Top, Side and Front.

Maybe this will be a good place to stop to make sure everyone is certain of what is going on.

Any questions so far?


We will eventually get to a place where this diagram will apply to what we are doing and (eventually) we will get to that vector relating to traction. Be patient. :wink:

This guy even uses an orthographic drawing as his avatar:

 

[SamSpeed]

Hah! I have always wanted to ride one of those!. Imagine one with a front hub motor! With that setup, I don't think it would matter at all where you put the batteries. That would be the least of your problems..

 

[safe]

Simplification

In order to make it easier to discuss the orthographic diagram I'm now going to simplify the picture to just the essential components. For now there is only one vector that points downward and represents the force of gravity acting on the bike/rider mass. I give it the label "A".

So far we have just one vector "A" the force of gravity.

 

[safe]

Momentum

Okay, now to make this a bicycle in motion we need to add a vector that represents the momentum of the bike/ride center of gravity. We do this by adding a vector "B" that faces in the forward direction.

The vector "B" is momentum.

 

[safe]

Flipping Over The Front

Now if we add a braking force that acts on the ground and it works in the opposite direction of the momentum of the bike/rider center of gravity we can see rather easily that there's nothing to prevent the bike from tipping over the front end. The design of the High Wheel Bike was inherently unstable on braking, but (as we will see) it was very good in other areas.

Okay, enough for one day... questions?

Observations?

 

[Dee Jay]

I can tell you're still wearing your lab coat, safe.

I don't understand why you're to putting us through more mental masturbation...

How about a more modern example...because nobody rides these High Wheel bikes anymore where a rider is 100% on top of the front wheel. Let's cut to the chase with ...say... a mountain bike, because it's what most ebikers tend to use as a donor <----I never liked this word "donor". Mountain Bike Ebikers also have the tendency to mount most (if not all) of the batteries in the triangle.

J

EDIT:
All scientific jargon aside, I think the answer is obvious: the lower the better, the way Deafscooter's scooters are set up, especially for lead users. The weight of led is probably best for traction and stabilty in races, but not for city riding.

J

 

[safe]

Don't worry I have the entire study guide roughly figured out. I just want to carefully and meticulously go step by step through the physics so that when the conclusions are arrived at there is no more:

"Well gee, I haven't a clue about physics, but I want to believe XYZ about steering geometry."

...we've suffered through the emotional side of the argument and now we are going through the scientific side.

Anyone who has a question about what has been presented so far (which is still very basic since I'm just getting the foundations laid) should raise questions right away. The advanced folks already accept the status quo of the "conventional wisdom"... so this is to convince the "rebels" like "John in CR" and maybe give him a better understanding about how vectors work and orthographic drawings etc...

And if I were to be wrong (somehow) then the "rebels" could now prove their theories scientifically rather than just saying "just cause I want to believe".

The primary goal is to raise the level of the discussion to math and science verses opinion.

Just be patient...

 

[johnrobholmes]

I just added a third more weight in batteries to my bike. Put them on the top tube, stacked on up on previously mounted batteries. 18s a123 baby! The bike was noticeably heavier to carry around, but no harder to push around. It did not ride any different than before. I even took it offroad. Seems like the convention of having a "gas tank" is the best place for a well handled bike at all speeds.

 

[safe]

Seems like the convention of having a "gas tank" is the best place for a well handled bike at all speeds.

Chalk one up for the "conventional wisdom".

Yes, the only negative with the gas tank location is that at the slowest speeds and when parked it tends to make the bike easy to tip over. At 50 mph it's ideal, at 5 mph it's not. The "conventional wisdom" is best at the highest speed and over bumps and taking turns.

 

[johnrobholmes]

Seemed to be fine at 2mph in the offroad too. It never felt tipsy.


I would equate it to balancing a weight on a stick when low speed riding. The longer the stick, the easier to keep the weight in check by moving the stick at the bottom. To move the "stick" I just steer left and right through the creeks and around the rocks and such.

 

[John in CR]

Safe,

You want to stick to math and physics fine, but stick to topic for once!

I'll summarize my 2 points, since they're buried in a number of long posts and some of my view has evolved during the thread. Keep in mind that this is wrt typical upright bicycles and typical riding.

1. The "roll axis" is NOT the be all to end all. The "roll" that you guys have been talking about results from countersteer. Countersteer on a bike is usually very small, and much of the lean for a turn is often accomplished by the bike "falling" into the turn after the imbalance in that direction is created by the countersteer. The rotation during the "fall" is the entire bike around the axis at the contact patches.

2. A bike balances relative to the ground, therefore you must look at its CG relative to the ground, and I mean the CG of the bike+rider, not the bike alone. If you place an added weight (eg batteries) at the CG it will remain unchanged. As you place the added mass lower, it lowers the CG, but only to a certain point. This is because that mass has less energy potential from gravity relative to the ground the lower it is placed, so it has less effect on CG. As you place that mass lower and lower, the CG of the bike moves higher until it returns to the original CG once the CM of the added mass is at the ground.

I challenge you to present a valid argument refuting either of these points. Don't try to change the subject and talk about momentum, because the point has already been established that extremely low placement can cause the tires to slide out during a curve for no other reason than greater centrifugal force. Discussion of motorcycles is irrelevant, since their greater mass and lower CG makes us ride them quite differently than a bike. This is real world physics not opinion, and both points are important in understanding the effects of different battery placements, and your derogatory comments only highlight your fundamental lack of understanding of the subject matter.

John

 

[johnrobholmes]

If you place an added weight (eg batteries) at the CG it will remain unchanged. As you place the added mass lower, it lowers the CG, but only to a certain point.

John

Wrong Wrong Wrong!!! This is where all of your misunderstanding stems from. The lower the batteries, the lower the CG and the further the bike has to lean to corner. Even at super slow speeds the front tire must track further to catch a falling bike when the CG has been lowered. Furthermore, a bike with batteries slung low will have a much harder time turning since the battery mass must move a further distance with each "countersteer". The weight needs to be close to your body CG for decent handling at any speed. The faster the bike travels the more imperative that the CG of bike and body be as close as possible.


I don't perceive a "counter" steer when I corner, but technically the initial lean when CG, inertia, and turning is not balanced would be consider the countersteer portion of the turn.

 

[John in CR]

If you place an added weight (eg batteries) at the CG it will remain unchanged. As you place the added mass lower, it lowers the CG, but only to a certain point.

John

Wrong Wrong Wrong!!! This is where all of your misunderstanding stems from. The lower the batteries, the lower the CG and the further the bike has to lean to corner. Even at super slow speeds the front tire must track further to catch a falling bike when the CG has been lowered. Furthermore, a bike with batteries slung low will have a much harder time turning since the battery mass must move a further distance with each "countersteer". The weight needs to be close to your body CG for decent handling at any speed. The faster the bike travels the more imperative that the CG of bike and body be as close as possible.


I don't perceive a "counter" steer when I corner, but technically the initial lean when CG, inertia, and turning is not balanced would be consider the countersteer portion of the turn.

John,

It's only wrong if I'm misunderstanding the effect of adding weight AT the original CG. If that creates less lean needed for the same turn than with no added weight, then yes I agree that the lean required is greater with lower placement, however, extremely low placement only gets you to where you have the same required lean angle as with no added weight at all. Regarding countersteer, I've maintained all along that it's generally insignificant, so the effect of changing it's direction at so little increase in angle is insignificant with a near rear tire patch placement.

John

 

[Tiberius]

As you place the added mass lower, it lowers the CG, but only to a certain point. This is because that mass has less energy potential from gravity relative to the ground the lower it is placed, so it has less effect on CG. As you place that mass lower and lower, the CG of the bike moves higher until it returns to the original CG once the CM of the added mass is at the ground.

John,

Read that again, please, and think about it. It is absurd. It does not correspond with either the maths and physics of the situation, nor with any intuitive feeling.

Nick

 

[johnrobholmes]

All I can do is laugh at this point. Somehow adding weight to the bike near the rear tire defies laws of physics for John. Potential energy has nothing to do with this at all. Center of gravity and the corresponding lean angle have everything to do with turning a bike. We can throw in centralization of mass too, but I am throwing salt into the sea at this point.

 

[John in CR]

As you place the added mass lower, it lowers the CG, but only to a certain point. This is because that mass has less energy potential from gravity relative to the ground the lower it is placed, so it has less effect on CG. As you place that mass lower and lower, the CG of the bike moves higher until it returns to the original CG once the CM of the added mass is at the ground.

John,

Read that again, please, and think about it. It is absurd. It does not correspond with either the maths and physics of the situation, nor with any intuitive feeling.

Nick

No it's not absurd. It becomes intuitive with the correct perspective, and that is that a bike balances relative to points anchored at the ground. According to the perspective that you guys have, if you take a mass and split it in half. Put half at the ground directly below the initial CG and the other half twice as high as the CG, and your CG will remain unchanged. It would be absurd to try to say that balancing (handling for a bike) remains unchanged. My correct perspective will tell you the CG is higher. This is also why those calculators can't come up with the correct answer with very placement of additional mass. Maybe CG is the wrong term for use to use, but we're definitely talking about the same thing. I suggest you guys step back and try on a fresh perspective, because I assure you that weight added at the contact patch has zero effect on the CG of a bike with it's wheels on the ground. Pick the bike up and everything changes, but then the bike is no longer a body in motion balancing with wheels on the ground.

Come on, you guys are intelligent and can get this.

John

 

[johnrobholmes]

CG would remain unchanged. Distribution of mass (centralization) would be changed and make the vehicle sluggish because of the weight far away from the CG, AKA the pivot point for leaning the bike.

 

[johnrobholmes]

fuckin A man, have you even tried to ride a bike with weight down low? I can tell you that it is slow to turn!! Add additional weight up top and CG can be back at normal, but the added mass up top and down low take longer to move!!

 

[John in CR]

A leaning bike pivots on its wheels.

 

[johnrobholmes]

Only if you aren't moving. It pivots at the CG with any speed, guaranteed. The tires are not directly under the CG when turning, they have to move from underneath.


Weave back and forth on your bike while trying to hold a straight line. The bike tires move underneath the CG to keep the center of mass (weight) going straight. If your bike is nimble enough you can keep a practically straight bearing while having the bike going everywhere. Ever seen a race bike get the wiggles? Rider and bike go straight and the tires are not!