Lightweight motorcycle build. The HillFighter project

[ArtemT]

Hi everybody!
After a long and painful hesitation finally started to design a lightweight electric motorcycle based on bicycle components. The main goal - to make a light (less than 40kg) and durable device for fascinating offroad travelings. Motor axis coincides with the axis of the swingarm, so I do not expect difficulties with tension / slack of the chain while riding off-road. The battery will be placed over the frame (under the seat) in aluminum housing - according to preliminary estimates in two rows I will be able to fit there no less than 200 of 18650 elements. I understand that the center of gravity is a little bit high – but on the other hand, there are successful projects with even higher center of gravity (Kuberg Freerider). The controller, for better cooling, will be placed under the seat.

To date, a frame 3D model is ready, and I’m choosing a contractor who will make individual frame components.

 

[recumpence]

I would mount the battery lower, possibly in front of the motor. The bike will handle far better with the weight lower.

Matt

 

[SlowCo]

Matt (recumpence) knows what he's talking about and should have added a link to his motoped build. And that is just one of his awesome build...

look here: https://endless-sphere.com/forums/viewtopic.php?f=28&t=62040&hilit=motoped

 

[ferret]

If that whas the syle of ride I was looking for, I would buy a LMX.
http://www.lmxbikes.com/en/
Why build something from scratch if it is available?
I would build only if what I wanted wasn't available off the shelf.

Avner.

 

[ArtemT]

I would mount the battery lower, possibly in front of the motor. The bike will handle far better with the weight lower.

Yes, I agree that lower battery placement will improve manageability, but I fear that the battery will be more vulnerable in this case - I plan to use the bike for an aggressive off-road driving

 

[ArtemT]

If that whas the syle of ride I was looking for, I would buy a LMX.
http://www.lmxbikes.com/en/
Why build something from scratch if it is available?
I would build only if what I wanted wasn't available off the shelf.

Avner.

I believe that this approach is fundamentally wrong - whatever goods we took, there are dozens and hundreds of manufacturers that offer it for sale - if we follow your logic, why would they all should exist and produce virtually the same product? Perhaps I can make cheaper than http://www.lmxbikes.com or lighter, or faster, or something else? I think it's called competition, and it makes our life better.

 

[recumpence]

I would mount the battery lower, possibly in front of the motor. The bike will handle far better with the weight lower.

Yes, I agree that lower battery placement will improve manageability, but I fear that the battery will be more vulnerable in this case - I plan to use the bike for an aggressive off-road driving

Just put a bash guard under it. Trust me, you really want that heavy battery down low.

 

[ferret]

I believe that this approach is fundamentally wrong - whatever goods we took, there are dozens and hundreds of manufacturers that offer it for sale - if we follow your logic, why would they all should exist and produce virtually the same product? Perhaps I can make cheaper than http://www.lmxbikes.com or lighter, or faster, or something else? I think it's called competition, and it makes our life better.

Sorry if I come off as negative. My experience with various projects taught me that in most cases buying something is faster, cheaper and easier to repair or replace than fabricating something similar, leaving more time, money and energy to fabricate things that can't be bought.

Disregard everything I wrote if your goal is just to make your own bike, but if the goal is to have, use and enjoy off road riding, take a look at all the options available before committing to such a big project.

I built my projects because no one made something with the features I was looking for, certainly not dozens or hundreds manufacturers. The same can be said for other builds here on ES. Unless I missed some advantage inherent in your concept, it's functionality and visually almost identical to the LMX.
Look at how much time money and effort has gone into the LMX, how many prototypes were made. I think you will have to invest just as much if not more to make something that is as good/better. Did you estimate how much time and money it will take to implement your design? I doubt it will be cheaper, unless you have free access to something like a machine shop with materials and knowledge to go with it.

Your target weight of 40 kg. is heavier than their claimed 38 kg. Speed is determined mainly by motor and batteries, not which frame you use.
In other words, does your (untested) design have an advantage over what is currently available in the market justifying making it from scratch?
If it's something specific, buying a frame and modifying it to your needs might be the most efficient rout.


Avner.

 

[ArtemT]

I would mount the battery lower, possibly in front of the motor. The bike will handle far better with the weight lower.

Just put a bash guard under it. Trust me, you really want that heavy battery down low.

When I was thinking about where to place the battery, I took as an example Kuberg Freerider (http://kuberg.com/freerider.html) - if we compare position of its battery, with my battery option, we can see that the freerider battery and center of gravity is even higher than in my version. I'll try to lower the rear shock and move the battery a little bit down.

 

[recumpence]

[/quote]
Just put a bash guard under it. Trust me, you really want that heavy battery down low.[/quote][/quote]
When I was thinking about where to place the battery, I took as an example Kuberg Freerider (http://kuberg.com/freerider.html) - if we compare position of its battery, with my battery option, we can see that the freerider battery and center of gravity is even higher than in my version. I'll try to lower the rear shock and move the battery a little bit down.[/quote]

Yes, I agree. They are using a poor center of gravity on their bike as well.

You can do what you want, however, low Center of gravity is always a good thing on any wheeled vehicle.

 

[E-geezer]

I'd worry about the torsional stability of a frame made out of a single round tube for high powered, offroad use.

 

[ArtemT]

I'd worry about the torsional stability of a frame made out of a single round tube for high powered, offroad use.

Well, I hope that this tube will withstand any load - it is 50 mm in diameter and thickness of the wall is 4 mm. In addition, I take the example of pitbike frames that constructed in a similar way

 

[ArtemT]

I believe that this approach is fundamentally wrong - whatever goods we took, there are dozens and hundreds of manufacturers that offer it for sale - if we follow your logic, why would they all should exist and produce virtually the same product? Perhaps I can make cheaper than http://www.lmxbikes.com or lighter, or faster, or something else? I think it's called competition, and it makes our life better.

Sorry if I come off as negative. My experience with various projects taught me that in most cases buying something is faster, cheaper and easier to repair or replace than fabricating something similar, leaving more time, money and energy to fabricate things that can't be bought.

Disregard everything I wrote if your goal is just to make your own bike, but if the goal is to have, use and enjoy off road riding, take a look at all the options available before committing to such a big project.

I built my projects because no one made something with the features I was looking for, certainly not dozens or hundreds manufacturers. The same can be said for other builds here on ES. Unless I missed some advantage inherent in your concept, it's functionality and visually almost identical to the LMX.
Look at how much time money and effort has gone into the LMX, how many prototypes were made. I think you will have to invest just as much if not more to make something that is as good/better. Did you estimate how much time and money it will take to implement your design? I doubt it will be cheaper, unless you have free access to something like a machine shop with materials and knowledge to go with it.

Your target weight of 40 kg. is heavier than their claimed 38 kg. Speed is determined mainly by motor and batteries, not which frame you use.
In other words, does your (untested) design have an advantage over what is currently available in the market justifying making it from scratch?
If it's something specific, buying a frame and modifying it to your needs might be the most efficient rout.


Avner.

Well, actually I have long wanted to do something like that, and looking at the success of other projects, I thought - why not? I do not plan to outdo anyone, and I understand that it takes time and money to implement such a project. On the other hand, I can not say that I'm starting this project from scratch - I rely on the experience and knowledge of other people who have already passed this way and made a lot of mistakes, which I"ll try to avoid.

 

[MitchJi]

Well, actually I have long wanted to do something like that, and looking at the success of other projects, I thought - why not? I do not plan to outdo anyone, and I understand that it takes time and money to implement such a project. On the other hand, I can not say that I'm starting this project from scratch - I rely on the experience and knowledge of other people who have already passed this way and made a lot of mistakes, which I"ll try to avoid.

Your seem a be determined to avoid following Matt's advice about battery placement. Not an auspicious start!

 

[Chalo]

I would mount the battery lower, possibly in front of the motor. The bike will handle far better with the weight lower.

Track racing motorcycle designers try to place the bike's center of mass close to the rider's center of mass, and vice versa. That means putting the bike's CoM much higher than they could do otherwise, but it's proven to work. The idea is to minimize the system's inertial moment by concentrating bike and rider mass around the dynamic roll center.

So for relatively slow, standing-up-on-the-bike riding, you're right; but for higher speed paved surface riding, there is a different approach that can yield better results.

I've noticed analogous benefits to loading cargo on a pedal bike in front and rear baskets rather than low slung panniers. Low mounting is best when you're not moving very fast, but once you start leaning through turns it's better to carry the weight high.

 

[recumpence]

I would mount the battery lower, possibly in front of the motor. The bike will handle far better with the weight lower.

Track racing motorcycle designers try to place the bike's center of mass close to the rider's center of mass, and vice versa. That means putting the bike's CoM much higher than they could do otherwise, but it's proven to work. The idea is to minimize the system's inertial moment by concentrating bike and rider mass around the dynamic roll center.

So for relatively slow, standing-up-on-the-bike riding, you're right; but for higher speed paved surface riding, there is a different approach that can yield better results.

I've noticed analogous benefits to loading cargo on a pedal bike in front and rear baskets rather than low slung panniers. Low mounting is best when you're not moving very fast, but once you start leaning through turns it's better to carry the weight high.

Your assumption is incorrect. With a higher Center of mass it's not rotational energy, but moment of inertia that is an issue. When you're dealing with rotational Mass centralizing it is best. However, we're dealing with moment inertia such as with a lever, moving the man nearest the point of pivot is best. The tire's contact patch with the ground is that pivot.

 

[litespeed]

I would agree that the closer the weight is to the pivot point whether moving fast or slow the easier it is to control. Put a 1 lb weight on the end of a 1 foot stick and wave it around. Then put the same weight on a 3 foot stick and wave it around. It will be harder to start the movement and then slower to stop it with a much farther distance to move.

With Matts correct scenario the pivot point is tire against street/dirt and the farther you get away from the pivot point....see above.

Now if we were doing stunts such as flipping the bike, wheelies, stoppies having the weight closer to the rider makes the mass easier to control because now the pivot point is you!

Great discussion but to the original poster if you want to do it your way go for it. We all learn in our own way.

Tom

 

[Chalo]

You gotta remember that when you maneuver a two wheeler, you're swinging the wheels out from underneath you and not the other way around.

 

[DingusMcGee]

Recumpense is correct. For ease of control placement of weight low and between the wheels is best -- but above the skid plate for other reasons.

As the wheels are turning on the dirt there is a point on them that touches the ground and unless the the wheel is slipping this is the instantaneous center of motion and the instantaneous velocity at this one point of contact is zero with respect to the earth. A similar instantaneous point of contact is also the instantaneous center of motion for lateral rotations. There are 2 different rotational measurements that occur about the instantaneous center of motion that apply to rotational balancing and rotational acceleration and are used in predicting how things rotate. They are respectively known as the first moment of inertia and second moments of inertia. If the wheel is slipping the effective instantaneous center of motion for calculations is moved towards the axle but only for those physical forces calculated in that direction of slippage. So with total [100%] wheel slippage the instantaneous center is at the axle and the wheel would have no velocity of translation.

The first moment of inertia varies with the distance of the center of mass from the center of rotation and is concerned about how static balancing happens about that point. The second moment of inertia varies with the (distance x distance = distance squared) of the center of mass from the center of rotation and is concerned with the torques needed as to how fast the lean angle can changed about the center of instantaneous motion. Since both of these physical variables are measured from the ground it should be apparent that they get bigger for the farther you and the center of mass of the cycle is moved from the instantaneous center of rotation. Having to put more force for correcting out of path motion takes more energy and time when the C of M is high than when it is lower.

 

[recumpence]

Recumpense is correct. For ease of control placement of weight low and between the wheels is best -- but above the skid plate for other reasons.

As the wheels are turning on the dirt there is a point on them that touches the ground and unless the the wheel is slipping this is the instantaneous center of motion and the instantaneous velocity at this one point of contact is zero with respect to the earth. A similar instantaneous point of contact is also the instantaneous center of motion for lateral rotations. There are 2 different rotational measurements that occur about the instantaneous center of motion that apply to rotational balancing and rotational acceleration and are used in predicting how things rotate. They are respectively known as the first moment of inertia and second moments of inertia. If the wheel is slipping the effective instantaneous center of motion for calculations is moved towards the axle but only for those physical forces calculated in that direction of slippage. So with total [100%] wheel slippage the instantaneous center is at the axle and the wheel would have no velocity of translation.

The first moment of inertia varies with the distance of the center of mass from the center of rotation and is concerned about how static balancing happens about that point. The second moment of inertia varies with the (distance x distance = distance squared) of the center of mass from the center of rotation and is concerned with the torques needed as to how fast the lean angle can changed about the center of instantaneous motion. Since both of these physical variables are measured from the ground it should be apparent that they get bigger for the farther you and the center of mass of the cycle is moved from the instantaneous center of rotation. Having to put more force for correcting out of path motion takes more energy and time when the C of M is high than when it is lower.

Ya, what he said.

 

[gogo]

The placement of weight issue was hashed out long ago in the E-S forums. Despite recumpence's experience and skills, he's dead wrong and Chalo nailed it.

 

[DingusMcGee]

gogo,

Chalo has put the origin of his coordinate system on the center of his body/head. This is permissible in mechanics but you then have to use rotation matrices and translation matrices to get your measurements into a useful fixed frame to make calculations easy -- what I presented. You have to know the instantaneous centers of rotation to make these inertial rotation calculations. Chalo is perceiving relative motion and thinks he at the origin or center of rotation so therefore the wheels appear to be moving out from under him, but that is not the case. He is perceiving apparent motion.

 

[recumpence]

The placement of weight issue was hashed out long ago in the E-S forums. Despite recumpence's experience and skills, he's dead wrong and Chalo nailed it.

I am more than happy to let people make bad decisions and suffer the poor handling consequences. That's totally up to them.

I am not a physicist. However, I know what works based on use of the items I build.go ahead and build two bikes, one with a low center of gravity and one with a high center of gravity and let me know which one handles better.

 

[DingusMcGee]

If we look at an Enduro motor cycle we see it likely has a CofG higher than the CofG on Harley-Hog. Here is what is going on: In rough terrain a cycles greater suspension travel is deemed more important than a low CofG. Suppose you want 14" of travel on the front and rear. It sounds really great to have that much cushioning but that means your skid plate must be >14" above the ground otherwise you would can out on the skid plate when getting big air and you never could utilize that much suspension. Hence the high CofG. For Harley designs you would never design for that much Big Air -- so the CofG on a hog is quite low and they have good pavement handling and have only a few clearance problems while on pavement. It is a tradeoff to have big travel over ease of handling on Enduro cycles -- they are harder to manage but they takes the bumps great.

 

[WoodlandHills]

The placement of weight issue was hashed out long ago in the E-S forums. Despite recumpence's experience and skills, he's dead wrong and Chalo nailed it.

I am more than happy to let people make bad decisions and suffer the poor handling consequences. That's totally up to them.

I am not a physicist. However, I know what works based on use of the items I build.go ahead and build two bikes, one with a low center of gravity and one with a high center of gravity and let me know which one handles better.

Honda did that for you back in the '80s. They built a GP bike with the fuel tank under the motor to get the cg as low as possible. It was not successful. Probably because the handling of two wheeled mono-tracked vehicles is a hybrid of the two theories under discussion. The tires are simultaneously the pivot point as well as arcing laterally beneath the center of mass. Why is this so hard to understand? A few minutes spent watching the super slow motion video on MotoGP broadcasts will show this clearly: the two wheels move into and out of near perfect alignment as turns are initiated. Once the arc is established the wheels return to nearly perfect mono tracked equilibrium save for small steering corrections. Ditto on the straights. The closer to alignment the more the movement of the bike is biased towards the "pivot at the contact patch" side of things and the more the tires are out of line the more the machine is rolling about its center of moment.

It would be nice if the real world would conform to a single simple model, but life just ain't like that......