Frame Material

[sstein]

I am designing a rickshaw/pedicab for a friend of mine to have constructed. I am a little stuck on frame material. I am obviously limited to 1020 or 4130 but I am not sure which would be better suited. Also most rickshaws use square rather than round tubes which I am a little cautious about. Finally I dont know what tube diameter or wall thickness to use.

The max load will be about 400kg. If anyone Knows anything that may help please let me know. thanks

[Shaun H]

Well depending on whether or not you can get comprehensive property data then you should be considering what you need from the material. Strength? (Yield stress) Stiffness? Endurance limit? (Fatigue strength) Corrosion resistance? Cost?

It's down to you the designer to decide on which properties are most important in the application. I'm not familiar with either alloys so I can't give you my thoughts, even so it should be your own decision as it's yourself (and maybe your friend?) that need to decide on the specification.

Square tubes are probably used in most rickshaws since it is easier to work with than round tubes and therefore cheaper in labor (could also use cheaper mitre equipment).

EDIT: Although I should add, square and round tubes have different mechanical properties which will also impact on the design.

Edited November 6, 2010 by Shaun H

[sstein]

Well depending on whether or not you can get comprehensive property data then you should be considering what you need from the material.  Strength? (Yield stress) Stiffness? Endurance limit? (Fatigue strength) Corrosion resistance? Cost?

It's down to you the designer to decide on which properties are most important in the application.  I'm not familiar with either alloys so I can't give you my thoughts, even so it should be your own decision as it's yourself (and maybe your friend?) that need to decide on the specification.

Square tubes are probably used in most rickshaws since it is easier to work with than round tubes and therefore cheaper in labor (could also use cheaper mitre equipment).

EDIT: Although I should add, square and round tubes have different mechanical properties which will also impact on the design.

Thank you, you have just rephrased my question in the form on an answer and given no information to help. I know that it is up to me what properties the frame requires, but i thought it would be quite obvious that like a bike frame a rickshaw needs both strength and stiffness, what I was asking was if anyone could give me a starting point for what tube wall thickness and diameter i should be looking at

[Shaun H]

Thank you, you have just rephrased my question in the form on an answer and given no information to help. I know that it is up to me what properties the frame requires, but i thought it would be quite obvious that like a bike frame a rickshaw needs both strength and stiffness, what I was asking was if anyone could give me a starting point for what tube wall thickness and diameter i should be looking at

I was trying to give you the thought process to decide for yourself. It's pretty unlikely that someone here will have designed a rickshaw before and even less likely that they're going to be able to give you tubing specifications.

To rephrase what I was originally trying to get through; If you believe you are limited to just those 2 alloys, then you need to compare all their properties. You are correct, it is obvious a rickshaw needs strength and stiffness, but which is more important for your application? Does the rickshaw need to last a long time, if so you need to consider corrosion and fatigue limits. Is one considerably more expensive than the other? Is one more difficult to work with?

If you aren't familiar with these kind of design processes and you can't find some one with experience, then I'd advise you play it safe and use tubing around twice the thickness of standard cycle tubing.

[eskimo]

In bmx 1020 is very shit to put it mildly and 4130 is the bomb. 1020 is much cheaper, heavier and weaker. However what you want it for is entirely different to bmx so follow Shaun's advice and research what you actually want from a metal. I'm just going by bikes and parts in the bmx world so they could differ some what on the quality of material and tubes you're actually intending to buy.

[sstein]

I am basing my assumptions on the bike world as well, 1020 is weaker as you said but that just means thicker tube walls are required, I am not looking for someone to say 'this is the tube to use' I am justing looking fr some advice about where to start with tube wall thicknesses

[Rob Leech]

I am justing looking fr some advice about where to start with tube wall thicknesses

Around 1.6 mm should be more than enough in 4130, could probably go down to 1.2

Josh.

And personally, i'd stick with round

If you havent found them already-

4130-

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=m4130r

1020-

http://www.matweb.com/search/DataSheet.aspx?MatGUID=2740581369f3421dac0d8c91294b5935&ckck=1

Speaks for itself really.

Edited November 7, 2010 by Rob Leech