Material properties of a bicycle

[Undapori]

Summary:: Please help me to determine the thickness of the material of the bicycle given, i need a step by step procedure. I know the formula required but can figure out the forces acting and reactions on the bicycle. The weight of the person riding the cycle is estimated to be 70-80kg

Help me

 

[phinds]

Just FYI, "I need help" is about as useless a subject line as you could possibly find. I suggest changing it so that it has something to do with what you need help WITH.

[Mentor Note -- Thread title updated to make it descriptive]

 

[Baluncore]

Welcome to PF.

There are many things still unspecified.
1. Is it a folding frame, or why is the cross bar not triangulated to front ?
2. Is the structure built from round tube, elliptical tube or else ?
3. Is the material steel, aluminium or carbon fibre ?
4. The weak point is the tube with steering bearings, more detail is needed.
5. The quality of the track will multiply the rider's mass many times.
6. What are the unusual features of construction and use ?
7. Why are you reinventing the bicycle ?

 

[Baluncore]

More thoughts...
The front half of the frame is too floppy. As it is, it will become unstable at some speed, oscillate, and the frame will be destroyed.

The hinge needs to be implemented by two separated hinges with hinge pins in-line. When riding, the rider's applies force to the handle bars, to oppose the forces on the pedals, or the rider will fall. That requires a much stronger link between the handle bars and the pedals.

The wheels are too small, so the pedals, (if it has them?), are too close to the ground. They will strike the road while leaning on corners. The pedal crank length is proportional to the length of the rider's legs. Only bikes for small children have short cranks and so can have small diameter wheels.

For rough surfaces you need larger diameter wheels to smooth the surface contact. Wide soft tyres are good on soft soil, but not good on rocky tracks.

The problems with bicycle frames is the joints between the tubes, not so much the thickness of the tube wall.

 

[Undapori]

Welcome to PF.

There are many things still unspecified.
1. Is it a folding frame, or why is the cross bar not triangulated to front ?
2. Is the structure built from round tube, elliptical tube or else ?
3. Is the material steel, aluminium or carbon fibre ?
4. The weak point is the tube with steering bearings, more detail is needed.
5. The quality of the track will multiply the rider's mass many times.
6. What are the unusual features of construction and use ?
7. Why are you reinventing the bicycle ?

1. Yes it is
2.That is yet to be decided, most possibly square bar
3.That is yet to be decided. (steel is 1st choice)
4.We just came up with this idea for our project. Please provide some insight if u can
5. Didn't quite get that
6.we are designing it to suit large office spaces, college campuses etc
7.It is needed because we are asked to bring novelty in our project ideas

 

[Undapori]

More thoughts...
The front half of the frame is too floppy. As it is, it will become unstable at some speed, oscillate, and the frame will be destroyed.

The hinge needs to be implemented by two separated hinges with hinge pins in-line. When riding, the rider's applies force to the handle bars, to oppose the forces on the pedals, or the rider will fall. That requires a much stronger link between the handle bars and the pedals.

The wheels are too small, so the pedals, (if it has them?), are too close to the ground. They will strike the road while leaning on corners. The pedal crank length is proportional to the length of the rider's legs. Only bikes for small children have short cranks and so can have small diameter wheels.

For rough surfaces you need larger diameter wheels to smooth the surface contact. Wide soft tyres are good on soft soil, but not good on rocky tracks.

The problems with bicycle frames is the joints between the tubes, not so much the thickness of the tube wall.

Thanks for the reply
Even though I'm embarrassed to admit that I'm final year student in b-tech and doesn't know half of the practical applications, you pointed out pretty good weak points. This design is just a rough model and we are still in the beginning phase. So you are saying that the folding mechanism should be changed and the ride height should be adjusted. Right? If you could direct me to some website where the approximations of the frame are done, it would be helpful

 

[anorlunda]

Even though I'm embarrassed to admit that I'm final year student in b-tech

f you could direct me to some website where the approximations of the frame are done, it would be helpful

No need to be embarrassed. We all had to start somewhere. But one thing to learn is to define what you are trying to accomplish before getting involved with design details.

If part of the purpose is to learn, then finding a website with approximations is probably not what the teacher wants you to learn. The same applies to finding formulas. Engineers would not use a formula unless they first understand the physics and assumptions behind the formula, because it could be the wrong formula.

I also guess that finding the minimum strength tubes is not an objective of the lesson. If you had the forces and reactions, what would you do with them?

So please step back and take a breath. What is the purpose of this project?
What things are you supposed to learn?

 

[Lnewqban]

Welcome, Undapori!
To be a student is no reason to be embarrassed.

Being a dynamic vehicle, a bicycle has some requirements of balance and control.
Please, read through these articles to learn about those:

https://en.m.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry

https://en.m.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics

It seems that your rough design has an electrical motor connected to the front wheel and that the frame is foldable in half for storage.
Are you required to design each part of this bicycle or only to create a rough drawing?

 

[Undapori]

No need to be embarrassed. We all had to start somewhere. But one thing to learn is to define what you are trying to accomplish before getting involved with design details.

If part of the purpose is to learn, then finding a website with approximations is probably not what the teacher wants you to learn. The same applies to finding formulas. Engineers would not use a formula unless they first understand the physics and assumptions behind the formula, because it could be the wrong formula.

I also guess that finding the minimum strength tubes is not an objective of the lesson. If you had the forces and reactions, what would you do with them?

So please step back and take a breath. What is the purpose of this project?
What things are you supposed to learn?

I would proceed to find the stress associated with flexural formula and search for the material which falls within the parameters
My main problem is the free body diagram of the said bicycle and the resultant stress

 

[Undapori]

Welcome, Undapori!
To be a student is no reason to be embarrassed.

Being a dynamic vehicle, a bicycle has some requirements of balance and control.
Please, read through these articles to learn about those:

https://en.m.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry

https://en.m.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics

Are you required to design each part of this bicycle or only to create a rough drawing?

Yes we have to design each part
Our proffesors are ridiculing us and others for bringing googled projects and stuff so we really want to work on this and make it something that we can be proud of

 

[Lnewqban]

Yes we have to design each part
Our proffesors are ridiculing us and others for bringing googled projects and stuff so we really want to work on this and make it something that we can be proud of

I would recommend starting by studying the details of some successful commercially available designs.
Please, see:
https://www.bicycling.com/bikes-gear/a20048132/best-folding-bikes/

The most common solution is a 20-inch wheels bike.
Note the main horizontal tube, which must be robust enough to stand the bending and twisting forces of the road.