Mounting your battery, Center of Gravity.

[John in CR]

SteveCA,

You're absolutely right that your real world experience with trouble free mileage trumps the guesswork that some of us like to think is theory. If your pedal would hit first and doesn't then you've got the clearance. It was hard to tell from the posted pic, but now that I looked at your avatar, I can see that you really planned it well. That bit of tilt all but eliminates the risk even if the box touches the ground, since the rear corner would touch first. They're also smaller and higher than they appeared to be in the higher angle thread picture.

With about 30lbs (I assume those are 48V) low on your front wheel and no appreciable handling issues, that's good enough evidence for me that low is better, especially since it's so much better moving the bike around with feet on the ground. I'm just glad to hear our thin foil cells hold up well to getting jostled around the maximum possible as long as the pack as a unit is well secured. I'd still like to see some aero treatment. In my case, I plan at least a small fairing anyway, so now I'm going to look at which is easier, splitting the pack saddlebag style or building a frame to support it in front of the headset and make the fairing part of the batt box.

Thanks for sharing.

John

 

[E=IR]

Have the boxes affected steering at all?

 

[safe]

Just because the rear wheel doesn't go straight, doesn't move the rear end roll axis off the ground other than the tiny amount resulting from tire flex.

You're still not getting it...

While we agree that the true path is complex (hard to define) we can also agree that the roll is not centered at the tire contact patch because (obviously) the tire is deviating from the straight line path. (as can be discovered with the puddle test)

If the rear wheel deviates, you can't use a simple contact patch model... no way...

So we have to place the rotational axis up a little higher... maybe it's only a few inches above the contact patch at the rear wheel, but the "standard" is to place it at the rear axle. I'm saying it's "approximately" that high... but we can certainly agree that it's NOT on the ground.

No way on that...

Do you accept that it's somewhere above the contact patch?

(you might need to go outside and actually do a puddle test to convince yourself)

 

[John in CR]

Safe,

No, you're the one not "getting it". The REAR of the axis of roll has to be anchored at the contact patch, except if 1. The rear wheel slides out 2. the rear wheel flexes left or right during a turn, which would move the axis very little, and because this would occur during the turn not during the countersteer the axis would typically be below the street. As we agreed before, and you were probably pretty close in one drawing with its highest point in normal riding, the front of the roll axis moves up and down. After the countersteer that sets up the lean necessary to turn on 2 wheels, the front end of the roll axis goes rapidly to the ground. It's only because the front wheel turns during countersteer that the front end of the axis is above the ground.

If you built a bike that steered with turning of the rear wheel and front wheel fixed, then the roll axis would stay on the ground, because countersteer would be impossible. I don't, however, suggest you build one because it would be very unstable, and you have enough trouble staying on the road as it is.

I challenge you to come to an understanding of this AND admit how you were wrong. I know, it's a difficult task, but you'll grow because of it, and maybe even earn a little bit of respect from your detractors in the process. I'll even give you a bonus question. There is a set of conditions that could cause the rear of axis to be above the ground without the rear wheel slipping out; explain how this can happen. Note: an airborne bike doesn't count, both tires must remain on the ground.

tick tock

John

 

[safe]

http://www.history.com/shows.do?action=detail&episodeId=331922

"Nothing combines human engineering with the tactile thrill of speed and power like the motorcycle. But what are the basic physics of the machine, and more importantly, those experienced by the rider? From the first steam-powered bike to the latest in hybrid technology, uncover the history science behind the excitement as engineers unveil their latest creations. If you've always wanted to know what a "power to weight ratio second to none" is, look no further. Daniel H. Wilson hosts."

They covered countersteer and even had an animation that proved my point... it's like this:

If you watch the show and see the animation of countersteer you will understand that it's exactly as I've told you. Trust me, if there was any possible way I would be wrong on this one I'd be humble and admit I was, but this is so central to bike handling (countersteer) that I think it's necessary for people to get it right.

Try to catch the next showing on the History Channel...

P.S: They even briefly brought up the issue of lowering the motor to SLOW the handling of a motorcycle. This was exactly what I had been discussing earlier. (road racers raised the motor in order to quicken the handling)

The funny thing is it's as though they made a show that covered every point I've made here as though they were saying:

"Yes safe, you are 100% right and here's a show that documents how completely right you are." :lol:

God must love me for some crazy reason.

 

[John in CR]

Sorry Safe but you get 2 strikes for trying to change the subject and introduce irrelevant material to support your incorrect assertion. Your drawing that shows headset to rear axle as the ideal line for placing weight, with forward and low along with rearward and high being the furthest from ideal, is wrong. Motorcycles typically place significant amounts of weight (the rider and the motor) exactly in locations that you say are bad. You'd think with decades of R&D they would have figured out something so basic. Then you supported this assertion with the premise that this line was representative of the roll axis during turns, which is also incorrect. Now you laughably use the obvious fact that the rear wheel follows the front one around as proof that you were right.

I suggest you grab a bike, move it around both with the front wheel straight and with it turned. Ride it around (with no big oncoming trucks or other traffic) in an open space and pay close attention to what goes on with the angles and roll axes of the bike during turns. While understanding this won't tell you definitively where batteries should be placed for best handling, it will offer some assistance in the decision process.

As a show of good faith I'll give you the answer to the bonus question. In order to lift rear part of the roll axis above the tire contact patch, just make the bike waggle (for lack of a better term) by slightly turning the handlebars back and forth. This will introduce flex in the rear tire and spokes, so the rear of the frame rotates around a point that is slightly above the ground. Otherwise the rear of the frame rotates around the tire contact patch, and without some kind of flex or slip that point remains the same. Yes, the line of the axis is constantly changing in a complex mathematical manner dependent upon the turn radius, the amount of countersteer vs weight shift relative to the frame, speed, frame geometry, etc., but none of that changes this simple relationship.

Note that this doesn't consider the impact of riding up on the side of the tire during a turn, but that impact is insignificant with a bike tire, and it moves the roll axis below the street surface under the rear tire anyway.

Let's see what irrelevant arguments you dredge up this time.

John

 

[Miles]

God must love me for some crazy reason.

Because no one else does?

 

[safe]

Could Someone Tivo The Show?

The first showing was at the same time as the Democractic Convention so I suspect many people might have watched that instead. I found it while flipping the channels.

If everyone just watches the show pretty much EVERYTHING that has been discussed here was reviewed. (in my favor I might add)

It would be great if we could get parts of that show posted online... (the countersteer animation sequence being the number one most important)

http://www.history.com/shows.do?action=detail&episodeId=331922

Unfortunately the first two showings are already past and so we might need to watch for this one in reruns in the coming months. They always rerun it eventually.

 

[safe]

Motorcycles typically place significant amounts of weight (the rider and the motor) exactly in locations that you say are bad.

They discussed this very topic in the show. If you want to create a slow handling (stable) street cruiser or chopper you can place the weight of the motor BELOW that rotational axis and this will create a bike that wants to go in a straight line.

Road Racers push the envelope of performance and so they WANT instability in steering. Road Racers want the bike to roll very quickly because at 100+ mph the bikes simply don't want to turn at all... they prefer to go straight.

So my point is that if you want to build a perfectly "balanced" bike (something that a Road Racer would love) then you move that engine up a little to quicken up the steering.

If you want an imbalanced bike that is slower handling you can place the motor down low and that creates the cruiser sensation... slow, stable handling.

This was covered in the show...

On my bike the weight is hardly noticeable because I have it balanced along the theoretical rotational axis which goes approximately from the axle of the rear wheel through the top of the front wheel. Had I placed my batteries a few inches lower it would have made for a bike that would "feel heavier" when riding... which for some might be a good feeling... but it's bad for people that want to be able to get in and out of turns quickly.

"Good" and "Bad" can be subjective terms...

 

[safe]

God must love me for some crazy reason.

Because no one else does?

Exactly... god is like the natural force of positive energy that no matter how negative the world might get you still press forward with a good attitude. It should not matter if people like me or do not like me if my faith in what I'm doing is solid... which it is.

Countersteer Geometry

This is another diagram that shows the original bikes path and then compares it with the countersteer bikes path. You could get an approximate number (percentage) that would represent the steering geometry of the bike if you took the maximum divergence of the front wheel and then calculated backwards to find the rear.

Notice that at higher speeds the angles change!

The black circles represent the contact patches so at really high speed the bike might travel 50 feet doing NOTHING but the countersteer. When this happens the front and rear are almost at the same divergence. Conversely, at slow speed the divergence is large and the rear wheel is much less.

So think, think, think... it's more complicated than people are giving it credit... every factor effects how the bike handles.

 

[Ypedal]

Safe, consider this the last time i bother to comment on your ramblings...

1- we are discussing electric " Bicycles " not motorcycles...

2- Typing In Color and Various Fonts IS JUST AS RUDE AS POSTING IN CAPS AND SHOUTING Cut it out.

3- Keep posting in your own build threads and i might not Ban you before the day ends.. otherwise you have been publicly warned.

Yes.. i' ve had it with this man..

 

[SteveMush]

"Gentlemen"...... Frankly, I dont care a rat's butt about colored diagrams and the behavior of higher-speed, heavier motorcycles with heavier tires (more rotating mass at higher speed = much higher groscopic effect)..... Oh no, I'm doing it too!

Seriously, I'm WAY more interested in real-world feedback of how various set-ups re battery mass placement actually feel and behave when riding, not motorcycle theories that may or may not significantly apply to bikes with their much lighter structure and rotational mass.

Is there room in this discussion for any real-world feedback on this?

 

[lepton]

Oh my e-bike commute this morning I was thinking of this thread and my bike's handling, so I'll share.

I have my batteries and controller mounted on a rack above the rear wheel, and its about 20 lbs. I'm running a rear X5 motor at about 2600 watts peak at 70 volts nominal. The bike is a full suspension 2005 Specialized FSR XC. At low speeds, and especially from a stop, the bike will easily pull up the front wheel and become unstable (do a wheelie). I have to consciously go easy on the throttle to prevent this at speeds >10 mph. I could of course have a current limited do that for me, but that's another story.

I previously had this motor on a hardtail mountain bike, with the batteries mounted in the center triangle, running at 55 volts nominal. While my weight was on it (~135 lbs) the bike wouldn't want to jump up, and I don't remember the front wheel ever coming off the ground. The torque output was somewhat lower given the lower voltage, but the difference in handling is very significant, regardless.

On the flip side (no pun intended), having so much weight in the rear has one big advantage - it makes the bike much less likely to throw you over the handlebars. I've had to make a handful of very quick emergency stops, and the bike didn't miss a beat.

Otherwise, the bike is rough to handle while walking it, as said earlier in this thread. It really wants to fall over, so you do have a actively balance it and keep it up. I pick the bike up over some giant train tracks a few times a week, and lift it into pickup truck beds fairly often, and the weight distribution is pretty lousy for that. Almost all the strength of lifting goes into the very back, but you still have to control the front. Certainly do-able but far from ideal.

 

[John in CR]

Safe,
Strike 3, so I'm done with you on this topic. At least you add humor, though I'm sure it's unintentional. I found this particularly funny, "Trust me, if there was any possible way I would be wrong on this one I'd be humble and admit I was...", because I see it as the root of your problems around here. You never admit when you're wrong, you just change the subject and argue something different.


SteveMush,
I agree. I'm in the process of moving my 2 packs (about 11lbs ea) from a rack above the tire to one inside the triangle and the other split in half to be like saddlebags straddling the top tube just behind the headset. Once I get the split pack apart, I may see if I can hang it safe and secure in front/under the downtube near the crankset, not because I believe it to be a better place in terms of making my bike handle most like it does with no battery weight, which I do, but for 2 reasons. 1. To get the darn things out of the way and 2. To make the bike less top heavy. As myself and others have mentioned, with no argument even from Safe, where the batteries are located is a much bigger issue when you're off the bike than when you are on it, and on top of a rear rack can be like wrestling a pig. You can't just grab it with one hand at the center of the handlebar and walk it around.

I've also had 30lbs of lead on a rack welded to the chainstay on one side with a 10lb motor on a mount welded to the seat stay, and with the weight fairly low, even that unbalanced setup wasn't problematic. It actually felt almost balanced, because the batteries were closer to the centerline of the bike and the motor was both higher and further from the centerline. I never even noticed an imbalance while riding. Maybe I unconsciously adjusted my seat position a fraction of an inch to compensate. Walking the bike around was also a lot easier than with my rear rack mount despite being centered and lighter, however, I had issues with the stuff sticking off the sides. It was like having extra sets of pedals to bump into with my legs, though not as painful as metal pedals jammed into the achilles tends to be.

Now for the serious cyclists for whom every nuance of bike handling is important, I maintain that getting your battery weight down close to the roll axis of the bike makes the bike handle more like the bare bike does. That roll axis varies in the triangle between the 2 contact patches of the tires and about 2/3rds up toward the headset with the rear end of the axis anchored at the rear tire. Getting it there is the hard part, because you have clearance issues with the crank and ground, as well as front/rear weight distribution that you have to consider, not to mention that multiple frame members are in the way.

John

 

[steveCA]

As I stated in my first post on this subject... the front battery box arrangement has some distinct advantages and some real disadvantages.

The advantages are a much lower center of gravity overall, and a perfect weight distribution front to back, since my rear motor weighs 30lbs and the battery assembly weighs 30 lbs.

Some big disadvantages are 1) appearance, its pretty ugly. I'm doing some thinking about how to streamline it somehow. 2) handling is changed, but a small adjustment to riding style seems to cover that. 3) There is an unknown elevation of the "catastrophic failure" risk factor, since I have never tested this thing to failure. (I'm afraid I'm going to have to find a test dummy to do that!)

There has to be a better way to mount the batteries.... perhaps by using a total of 4 smaller battery boxes mounted at the ends of both front and rear axle..? four longer, shorter 10ah batteries for instance to get even more range.

SteveCA

 

[John in CR]

...There has to be a better way to mount the batteries....

There is, and it starts with a bike frame specifically designed to be an E-bike with a battery compartment inside the frame. There's more than enough room if designed that way, even space like a glove compartment and another for tools, battery charger, extension cord, etc. That's my next project as soon as I come to a firm decision on a drive train.

John

 

[Tiberius]

Safe,
Strike 3, so I'm done with you on this topic. At least you add humor, though I'm sure it's unintentional. I found this particularly funny, "Trust me, if there was any possible way I would be wrong on this one I'd be humble and admit I was...", because I see it as the root of your problems around here. You never admit when you're wrong, you just change the subject and argue something different.

Hi John,

Actually, I think safe is correct on the point in question. The roll axis is not at the rear tyre contact point. He's posted a perfectly good explanation of why that is so.

Nick

 

[safe]

Sometimes I think that the politics on this forum are getting so "politically correct" that when the truth is presented the online "collective truth" instead wants to stomp it out.

Countersteer does certain things.

1. It alters the path of the frame itself and makes both the front and rear wheel diverge from the original path.

2. Speed matters. At slow speed the front-to-rear path divergence is highest because the wheelbase becomes a significant percentage of the overall divergence path. At high speed (like 50 mph) you can travel for long distances with the bike gradually carving a line out from underneath you. The higher the speed the smaller the wheelbase percentage becomes relative to the path divergence. This means that the imaginary "rotational axis" changes with speed and the rotational axis becomes "more flat" with higher speed.

3. Braking can complicate countersteer because you are essentially pulling the rug out from under the bike in order to set up for a turn. If you overdo it on the brakes you can lose the front end.

...I could go on, but you get the point. What I've been saying all along is legitimate and does not only apply to motorcycles, it's for any two wheeled machine. (bicycle simply means "two" (bi) "wheeled" (cycle))

Bicycles (standard) are so lightweight that the weight of the bike is essentially zero. Electric bikes have a lot of weight (it can easily add 50 lbs) so the physics that apply to motorcycles start to creep into the ebike realm. All the mistakes made in the past on motorcycles are being reborn in this new ebike world.

"Those that forget history don't realize they are doing something wrong because history tends to be silent since they are all dead people now." :?

 

[gogo]

Since the system consists of bike + rider, the rider part of the equation puts the CG rather high and you would want to bring it closer to the roll axis by putting batteries low and centered between the wheels?

On a motorcycle the rider doesn't weigh 2 or 3 times as much as the bike.

Keeping the battery weight low and centered would also make it easier to handle the bike while not mounted on it.

 

[safe]

Keeping the battery weight low and centered would also make it easier to handle the bike while not mounted on it.

There is a subjective factor here as well.

What type of handling do you want?

Some might argue that a low weight placement will create a more stable ride (which is true) and that they don't need to be able to turn very rapidly. Very slow speed maneuverability is easier with the weight low, not high.

Others might argue that they want the quickest responsiveness possible and in that case you would want the weight up higher to be centered on the roll axis.

As long as we all "agree" on what effects these decisions have then we have "arrived" at a consensus. Low weight placement in the front tends to slow down the steering, but makes it feel more stable. (like a chopper or cruising bike) Higher weight placement speeds things up and is more suitable for people who want performance.

 

[John in CR]

Hi John,

Actually, I think safe is correct on the point in question. The roll axis is not at the rear tyre contact point. He's posted a perfectly good explanation of why that is so.

Nick

Tiberius,

Don't let yourself be drawn into "Safe logic", because no one knows what else lurks there. It may be the Twilight Zone for all we know, from which you are unable to return.

An axis by definition is a straight line. While this roll axis is constantly changing, other than with a tire slip, there's no getting around the fact that the axis line passes through the contact patch of the rear tire (ignoring tire and/or frame flex, and rolling up on the side of the tire). I can't draw a good graphic, so it's best to just go outside with your bike and see for yourself. You'll quickly see that moving or not the roll axis has to go through that point. The front is different because the front wheel turns relative to the frame.

John

 

[Tiberius]

Hi John,

I don't want to get into a discussion based on personalities; I don't see how that settles a technical question.

But I do think you should have a go at that graphic. You were persuaded to re-consider the roll axis before. The obvious first thought is that on the front wheel it is at the tyre contact patch, but once you looked at it you realised that its above that because the contact patch has to move sideways.

Surely, the same thing happens with the rear wheel. It too has to move sideways for the bike to lean. Maybe not as much as the front wheel, but in the same direction.

Nick

 

[Drunkskunk]

Seriously, I'm WAY more interested in real-world feedback of how various set-ups re battery mass placement actually feel and behave when riding....

Is there room in this discussion for any real-world feedback on this?

I prefer the weight up high. when seated on the bike, having the weight higher up means the center of mass is in a smaller area, and so the inertia is less when manuvering. tis a small detail, but you feel less stress in your hands and in your seat.
By an example, tie a 2 liter bottle of Coke to the bristle end of a broom, and try to sweep with it. then try it again while its tied up by your hand. Its a lot easier to sweep with it higher up, right?

Now, this has nothing to do with actual preformance, only with feel. having the weight low while sitting on the seat, to me, feels like sweeping with the bottle on the bristle end of the broom.

Now, standing up off the seat, that changes things. having the weight high feels unstable, especialy if the weight is over the back wheel.

Thats just my oppinion, and has nothing to do with actual preformance, just how it feels to me. We can discuss how to improve preformance elseware.

 

[lostcoyote]

safe,

can ya apply those differential equations to your bike and get any useful answers?

 

[John in CR]

But I do think you should have a go at that graphic. You were persuaded to re-consider the roll axis before. The obvious first thought is that on the front wheel it is at the tyre contact patch, but once you looked at it you realised that its above that because the contact patch has to move sideways.

Surely, the same thing happens with the rear wheel. It too has to move sideways for the bike to lean. Maybe not as much as the front wheel, but in the same direction.

Nick

A real world example is far better than any graphic I could ever do. Keep the front wheel straight and lean the bike left and right. Obviously it is "rolling" around the axis formed by a line between the 2 contact patches. Now turn the front wheel sideways, and allow the front wheel to roll one direction with the handlebars going the other. The front of the bike is rolling around a moving axis somewhere between the handlebars and the front wheel, but the rear of the bike is still rolling around the same point where the tire meets the ground. This is exactly what happens during countersteer. Turning the front tire gets it out from directly under the bike to induce a lean with little or no weight shift.

John