How should I connect axle, wheels and frame? how should be dimension of them( speciellt for axle and hole)?

Hello, Everybody!
Im a second year student, working on a design project. I am designing a water hose cart with 40 m hose(15 bar). I have finished my drawing, but i have problem with one part of this. It is about connection of axle,wheel and frame.
How big should be axle, and hole on the frame and wheels ( I craete two wheels, 200 dimension, i want to use plastic and rubber)?
Should i use scotter pin eller nut? which size should be If i use one of them?Or do you have better allternative for connect axel, fram and wheels them togather?
I know that i should use play and grip for this part , but i should decide how big should be my hole on frame, and wheels. So i have to know about how big should be my axle.
Can anyone help me with this part? Or can gauid me how i can find guidness for this part?
All help and advice would be really appreciated.

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5 Answers

A few factors would go into the design, but a general basis would be to calculate the loads in which you are going to be carrying, add in your safety factor, and then you will have some quantitative data to support whichever axle size or wheel you end up going with.

For example, if the cart is going to be used to transport 10lbs of material you may be able to use a much smaller diameter than a cart carrying 100lbs.

This is a general statement and wont work in every scenario, but should help you get close to the desired sizes.

https://www.mcmaster.com/#98355a010/=1bp4vf5
Here is a website where you can see the details for cotter pins and also the strengths of different axle materials. It gives you the hole sizes needed for the cotter pins as well.

A more detailed answer could be given if you are able to list more specifications for your project.

 
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Thanks for your answer, Mashi. More info:
It should be able to dirve the ”40 meters ½ water hose” on the uneven surface. The focus must be on a structure that is ecologically sustainable (low resource output/ low environmental.

*Perofesnal use( garden).
*Pressure:15 bar.
*Wieght of hose+ water= 11 kg.
* shouldnot cost more than 55 Euro(all component together).
I attach how it is almast looks like.

 
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I did some calculation, but i am not sure that is correct. It is my first construction project in the universitet. So it is not too easy. I did calculation for bending, safety factor 2 and stainless material for frame.
How should calculate for wheels?
Should i calculate 12 kg force on axle in the two wheels?

 
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I typically choose worst case scenarios when it comes to design loads. For example suppose the cart is positioned horizontally now supporting the load as a simple beam with reactions at the handle and tires. If a man were to kneel on it should it fail? This would primarily size the frame but the axle bearing loads on the stainless steel frame may yield the thru holes or bend the axle. Using your cost/weight allocations choose the optimum arrangement. Look at a furniture cart or other similar transport mechanism to get an idea of how they design those areas. For moving the cart on wet turf you may want a wider tire and for lower tractive effort in pushing the cart you may choose a taller tire. With these relatively small loads choose a tire and rim design that works in terms of diameter, bushing vs. bearing, rolling resistance on turf, pneumatic vs. solid core...etc.. I am not trying to complicate this design but rather to bring up some variables that are present beyond the free body diagram and should form a part of your thought process on this and future projects.

 
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If a client engaged me to design a hose cart along the lines of the one in your image and to a fixed cost, this is where I would start with sorting out wheels and axles. As I know the approx weight of finished hose reel with a hose attached I would look on the net to see the range of wheels available from local suppliers. This link is a local supplier of these parts. http://www.swc.co.nz/replacement-wheels.htm . From this I can select a suitable wheel for this purpose at a price and duty that fits the design brief. I would look towards a wheel with a larger, rather than a smaller wheel as this travels over rough ground easier and going for a wheel able to take the most load and fit within budget as this type of equipment gets knocked around in use. The wheel chosen will provide the details required for axle and choose the wheel fixing to be the most straight forward and therefore cost effective.

 
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