Let's Design 3 : DIY electric bicycle

I'm a semi-retired mechanical designer, and thought about building my own hybrid bike.  I would like to see a three wheel system to allow you to carry a bigger battery pack (longer range and better speed).  I would also like to see the rear wheel suspension tiltable  to allow safer turns and controlled from an input off the front wheel that tilts a specific degree of movement determined by speed and turn radius.  (electronic actuators and front fork angular position and accelerator speed detection with an arduino controller for hands off, no-human input for speed of reaction and accuracy of repeated adjustments.)  This would allow the battery pack to be on the main frame, (that doesn't tilt), but allow the motor(s) to be mounted with the tilt wheel(s) to allow simple belt/pulley drive train.

Hi John you mentioned tiltable wheels on a 3 wheeler for safer turning here is an idea I am just throwing out there , have you ever seen a wheel chair

that both wheels are tilted outwards at the bottom , this might give the stability you need, I agree any 3 wheelers are dangerous , like an HD with a side hack can make a left hand turn better than a right, a trike however is a flipping nightmare. as for the rear wheels tilting independantly I think that would much more complicated.

I have thought of doing a rechargeable moterized bike for some time the coolest one I've seen was run by a battery powered drill.

Hi John you mentioned tiltable wheels on a 3 wheeler for safer turning here is an idea I am just throwing out there , have you ever seen a wheel chair

that both wheels are tilted outwards at the bottom , this might give the stability you need, I agree any 3 wheelers are dangerous , like an HD with a side hack can make a left hand turn better than a right, a trike however is a flipping nightmare. as for the rear wheels tilting independantly I think that would much more complicated.

I have thought of doing a rechargeable moterized bike for some time the coolest one I've seen was run by a battery powered drill.

Tilting wheels are not all that difficult, mount each wheel on a hub in a bearing carrier set up, hinge the lower wheel carrier to the frame, and use an actuator to move the upper carrier in and out to tilt the wheel itself.  The tilt can be controlled with a simple 4-bit processor taking input off the front forks (amount of turn, and the wheels themselves, speed of movement)  This will generate a movement of the actuators to 'lean' the bike into the turn and increase stability immensely.  Tilting both rear wheels in at the top as on a wheel chair would add increased wear on the tire because the off load would be constant and wear out the tire faster.  The tilt frame would only induce that sort of wear in curves and the tire would be back up on the full tread for straight line movement.  I have a design for this, but the cost for me to make it without a current job is simply too great to make it happen.

Have you ever considered to have the rear wheels angled in to each other at the top (already mentioned by someone I believe, like on one of those "special" wheel chairs for racong paraplegics or similar), mounted in a frame that has two pivot points in the middle where it connects to the bike frame. That way the whole bike can be "laid over" for corners. Just supporting it with strong springs may be enough, combined with your body weight moving over" left and right" for corners, no electrics/electronics. The front wheel will be securely mounted to the frame and will tilt left and right with the frame of course.....

Keep the C of G low and I guess you will have a lot of fun.......

Firstly I freehand sketch, then I have an old drawing block that I use to get some ideas on paper, it helps to have it clear to look at I find.....I rarely use CAD, though I am always on the PC for other things. I like an eraser, a pencil and moveable set squares.....but that's just me...

You can drive the rear wheels with your electric motor, usually on a trike its best to only drive one wheel and let the other freewheel, even though both are on the same axle for strength. If both rear wheels are fixed on the same axle, you will get severe cornering problems. Look at any child's trike and you will see that I am right.....only one side is driven. Or use two motors, synchonised in some exotic manner or you need a proper back axle like in a car.

regards

Andy

Most 2-motor controllers actually handle the cornering situation by slowing the inner motor and speeding up the outer motor as the vehicle turns.  This was one of the first real improvements from the hybrid vehicle developments for car, and would work on a bike just as well.  As for the spring loading and the inward tilted wheels, remember that all the weight of the machine will be on the edge of the tilted tire and the wear will be one sided.  This can lead to dangerous situation as the tire is not constructed to handle much of that kind of loading.  Most of its wear strength is in  a plane perpendicular to the tread itself, (IE the tire sitting straight up and down like normal.)  This is a problem that will take some innovation, and a dose of electronics control to handle, just what this site promotes.  The tilted wheels like a wheelchair are an easy fix, but generate their own problems.  The processor controlled tilting of the wheels to match steering and turn requirements is going to give you better wear, safety, and handling.

What you say is actually quite wrong, you actually improve tyre wear dramatically, simply because when one side is worn, you swap it around so that you can wear the other side. Wearing in the middle only, as you suggested, allows only half the "distance"......or thereabouts.

Also, the road holding (I am assured!) is actually better, especially when the road is wet, believe it or not (I am told!!).

This is a trick that I learned from a handicapped sportsman who not only goes on marathons in a wheel chair, but plays basketball as well......all the chairs used have the tilted wheels for top cornering!! This picture shows how this is done.

Also the streses and strains of thse sports tell me clearly that this is a very stable and light method of being on 3 wheels without something breaking, though my contact did say that occasionally he has a "crash" which can result in welds breaking......they are not slow either, I have heard that some of these people can do a marathon FASTER than some runners!!! Not easy to believe for me.......

Some other parts of the design of these wheel chairs may also prove useful to the OP as well, low CG etc..

I hope this helps for better understanding of the forces involved....

Best Wishes

Andy

John and anyone else following this thread, I'm sure it can be done, No doubt you sound like a very intelligent person, but if you have a stable wheelbase like the chair pictured above that tires do wear evenly on, you would not need actuaters and springs that could fail and cause possibly a fatal accident.

But good luck with your design, but honestly I think you are just asking for problems that will increase the cost of the machine defeating the entire purpose of a cheaper means of travel.

Example: The Segway = what a fantastic machine I would love one, but where are they and why ?

I see a mall cop on one once in a while, but not many. Why because the cost was too high for that price it should fly.

I think the problem people want to solve is not to have to depend on oil, right?

Bikes are a great, but not up hill, the rechargeble electric motor solves that problem.

Here is what my daughter and I would love to see, an affordable bike with a motor that assists peddaling so we are still getting our needed exercise.

The motor and electrics should be configured as a self charging unit as the wheels turn and possibly a small solar cell to run blinking red rear LED lights and LED head light for safety.

If some one would design this in open source or if someone already has please link me to the plans.

I would build one first, test it and then build one for my daughter. I have a Huyndai and it costs over $30.00 to fill the tank with gas, I can't afford a hybrid car .

I am new to this site and I absolutely love it so far. Hope to make many friends . I will be adding more to my profile so you all can get to know me and find out what my hobbies are maybe we have something in common , I'm sorry I got a little off topic like I said I'm new here and learning . thanks for reading this.

Counting solar cells (check battery demand curves to see that you would need a very sizable solar cell bank just to provide motive power let alone charging.)  This is one of the very factors that make a solar driven vehicle so difficult to engineer!  The recharging from pedal power requires that part of your pedal input be converted to power (electrical) and so subtracts from the physical power to move you.  This is corrected by MORE physical power from you to maintain speed.  Right now that is why the vehicles with the longest ranges and highest speed and easiest mechanical life are those with power plants.

The Segways cost is reflective of the impressive electronic syste used to simply balance the two wheel unit.  A bike with three wheels is stable and needs only simple power control systems to render it responsive to the drive requirments.  I am looking at a design to move the bike into the realm of serious commuter usage on roads at road speeds with a low eco profile and a maximum of safety.  By leaning the bike into a turn you increase road safety and control, and allow you to use physics to give that to you.  This is not really complicated, and innovation will take the bike into new concepts that give us abilities we are onlyy beginning to see possible.

As a mechanical designer with a decade and a half of hands on experience, I can tell you that simple looking design is not!  The forces on the tilted wheel axle and frame is amazing, and if the frame is too light, broken welds are very easy! (consider the potential for injury when that happens, as you'd have no warning, and the whole thing would be over in seconds.  Do that in traffic and you have serious problems!)

You said: "What you say is actually quite wrong, you actually improve tyre wear  dramatically, simply because when one side is worn, you swap it around  so that you can wear the other side. Wearing in the middle only, as you  suggested, allows only half the "distance"......or thereabouts."

Wrong!  The tilted position brings the sidewalls of the tire into contact with the ground (something they are not designed for!) As the corner of the tread wears off due to the off line force, you are wearing through the thinner sidewalls!  The sidewalls are designed for flexing to dissipate heat, and provide a measure of suspension as the tread flexes to fit the ground contact point.  The thread is the thickest part of the tire and is designed to take all the wear of contact.  The sidewalls are not!   You are not extending tire life this way, you are shortening it, because once the thinner sidewalls are damaged, the tire will either burst or go flat and neither adds to the life of the tire.

The longest tire life is when the tread makes full vertical contact with the ground and the thinner sidewalls can do what they were designed for.  Wheel chair tires are often filled with a solid elastic material that prevents flats but adds a lot of weight.  I'm not trying to rain on your idea, but to explain that we have to deal with the forces involved, and the designs of the parts involved to get the max. out of them.

Completely wrong, you have to remember that tyres for two wheeled devices have a completely different profile to those for 4 wheeled devices (cars).....the tread actually is rounded for bikes (of ANY sort) and therefore you cannot start wearing the sidewalls. Car tyres are generally very flat treaded........

Go and look at any motorbike or pushbike tyre, as they are designed to go round corners (laying over) with full grip!!! Many have almost two "flats" at an angle with a small high center to allow more tread to touch the road when cornering than when riding in a straight line.

Many bike users would say that their tyres have more technology and knowhow put into them than any car or truck tyre.....

You sound like a car driver who has never had a bike of any sort, or you would not have posted in such a manner and so wrongly.......

To aid your understanding of the technology, I made a quick (bad quality sorry) photo of my (dirty) bike tyre for you, I think that it alone shows the princples of how bike tyres are made, just look how rounded it is:-

You can see just how much the tyre is curved around, to wear the sidewall, you would need to be almost lying flat on the road to even start doing the damage you are imagining....

I found a good source of infosand pictures for you here:- http://en.wikipedia.org/wiki/Bicycle_tire

Looking at motor bike tyres shows a similar design curve. How would you wear the sidewall on such a tyre as this for example (though motorbike tyres are seldom used on wheel chairs! But some specialist bike tyres are basically smaller, thinner versions of this:-

I hope this helps you to understand that your perceived problem is not a problem at all and will never be as few Wheel chair users have car tyres on their chair!!

Tyre wear when using the "sides" is less than when a bike is riding upright in many cases, being able to wear one side and then the other does in fact dramatically increase the wear usage of the tyres....

I am sorry that the picture quality is not great, but I am sure you get the idea, but if not, just ask, I and many others here will do our best to help you further.

Have a great day.

Regards

Andy

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You need to take into account something called camber thrust. When running with the tyre leant over the contact patch is in effect a section of a cone and wants to steer towards the frustrum. Rubber at the inside edge of the contact patch is running at a different speed to the outside edge creating drag (and wear). Two opposed wheels do of course want to run straight as they cancel each others camber thrust. It's all a comprimise between wheel and axle loads, drag and cornering grip.