Opinions on engineering class project

$nowMeansBroke · Nov 27, 2007

I am a Mech. Engineering student at SDSMT in South Dakota. One of my classes is a Product Development class, where teams of students form a fictional business and come up with a product to take through all of the steps of development.

Since 4 out of the 6 people in our group ride sleds, we decided to design a gas rack since the old ratchet straps and bungees aren't really cutting it anymore.

The design we came up with is to use a rail system, with blocks sliding onto the rail and pins to hold the blocks in place. We wanted to make a universal system that could potentially be used on snowmobiles, atv's, trailers, pretty much anywhere you want.

In reality, only one pin per item you want to attach would be needed. Instead of one per block, I just put that in the drawing for kicks.

The blocks would use 3M VHB adhesive tape on the top side, to allow a gas can, toolbox, cooler, etc... to be stuck to them. The reason we chose this approach is the ability to use any gas can you want, instead of having to buy an expensive custom made can.

Link to the VHB tape:
http://solutions.3m.com/wps/portal/3M/en_US/VHB/Tapes/Product-Information/Features-Benefits/

We are (hypothetically) planning on having them made from extruded HDPE, and offering them in a few standard lengths and also custom lengths for other applications.

So, please let us know what you think. Would you buy something like this? Is it a decent idea? What would you pay for say a set of 2 rails and 8 blocks?

Thanks for the help

LEE · Nov 28, 2007

Looks good, that should be a fun project. Make sure the design allows for some snow/ice buildup and can still be removed down the rails. Look at your minimum edge margin on the mounting holes in the plan view. Those will crack out with the vibration mounted on a sled tunnel.

CADman · Nov 28, 2007

Have you done an FEA on your components yet? What is the material and thickness of your rails? Will they be strong enough with large gas cans bouncing around while sledding? You should be able to determine a lot of factors in your DFMEA and though you FEA analysis. Good luck! Looks like a fun project.

Barnes · Nov 28, 2007

Looks like a good idea. Is Klanovic still teaching that class? If he is you don't need to worry too much about a FEA just a few simple calculations to make him happy. (shear stress in the pins, rough vibration analysis) I would try to find pins that are easily available and design the rails and block off of that. That way the only thing you have to manufacture two pieces.

vmaxfrank · Nov 28, 2007

If I'm understanding the use of the tape, you may not need to limit yourself to gas cans. You could use coolers, tool kits, etc on that as well, right?

$nowMeansBroke · Nov 28, 2007

Barnes said:
Looks like a good idea. Is Klanovic still teaching that class? If he is you don't need to worry too much about a FEA just a few simple calculations to make him happy. (shear stress in the pins, rough vibration analysis) I would try to find pins that are easily available and design the rails and block off of that. That way the only thing you have to manufacture two pieces.

Dr. Dolan is doing it this year, but it's still not bad at all. As far as FEA I ran it through the COSMOS package in SolidWorks once, just guessing at the loading. We made some design changes though so I'll be doing it again here shortly. The main focus of the project is the business aspect of it though, so the analysis is really just for our own benefit if we were to ever decide to actually make the product.

The pins will probably be changed to just a simple ball detent pin with a ring type handle or something like that, the ones I put in the drawing are a little bit spendy for what we want to do.

If I'm understanding the use of the tape, you may not need to limit yourself to gas cans. You could use coolers, tool kits, etc on that as well, right?

Yep, that was our plan, use any gas can you want, along with anything else you would want to carry with you.

What is the material and thickness of your rails? Will they be strong enough with large gas cans bouncing around while sledding?

At the moment we're thinking 1/8" or 3/16" extruded High Density Polyethylene for material for both the rails and blocks. When I ran the first analysis I just guessed at the loadings and came up a safety factor of 9 with the current design. I'm going to run it again shortly though so I'll post the results.

Look at your minimum edge margin on the mounting holes in the plan view. Those will crack out with the vibration mounted on a sled tunnel.

That's a really good point, definetely needs to be changed.

Thanks for all the help so far guys, keep the comments coming.

PistonBroke · Nov 28, 2007

tape

Are you sure even the sexiest two sided tape in the world will hold onto a 50lb gas can while a rider goes balls-out over 3' moguls?

nice concept though - kinda like the craiggerbilt system but more universal.

good work so far

modsledr · Nov 28, 2007

Existing System

I know you want to design a universal system, but a rail type system has already been done by Mountain Addiction.

http://www.klymazzation.com/snowmob...ain-addiction-bungeeless-gas-rack-track-rack/

modsledr

$nowMeansBroke · Nov 28, 2007

Are you sure even the sexiest two sided tape in the world will hold onto a 50lb gas can while a rider goes balls-out over 3' moguls?

The info from 3M looks pretty good, but without knowing the real life loadings and doing a lot of testing we really have no idea. The 2 sided tape was just the first thing that came to mind.

I know you want to design a universal system, but a rail type system has already been done by Mountain Addiction.

True, but you still have to buy their $40 jugs to go with it, and there isn't really any accomodation for attaching say a toolbox or cooler or whatever.

SylvanLaker · Nov 28, 2007

uhmw is a much better plastic for this application HDPE is not very good...

Ice Cap · Nov 28, 2007

I have a couple observations for you.
The extrusion/track may cause some problems for you. The lightening holes may ice up and restrict movement of the blocks. The extrusion also may be more complicated/expensive to manufacture than you need.
Why not use a simple T section? If you are going to use pins to attach the blocks I am sure the pins shear capability is more than enough to hold anything you could think of attaching to a sled or ATV.

I would also think twice about using ANY kind of tape. The loads you will see from a full gas can bouncing across moguls is probably way higher than you think!

Good luck with your project

KWB · Nov 28, 2007

BTDT - Design class was one of my favorite. I like the concept the details need some work to be a good product and a profitable company.

Lock the customer into your product line you have a lot more opportunity to make money selling cans, coolers, toolboxes, first aid kits, .... than just the rail and mounting kits, you can offer a base to let the customer modify as well to stick the odd stuff on.

I have used VHB in many cases for production volume parts-- wouldn't use it the way that you are proposing. Surface prep is very key as is the substrate (and you can't control what your customers would be sticking to). Low surface energy materials are going to be a royal PITA. Use geometry to nest your parts on the bottom and at least two sides.

First your "pad" that the can/cooler/whatever sits on is fairly small letting the mass above get into a peel mode with the dynamic effects. You basically have a pedistal that the mass is now swinging around on above your tunnel more severly stressing the attachments there... to borrow from pontiac "wider is better"

Eliminate the cross drilling in your base extrusion-- extrusion is cheap, secondary operations eat money fast. Make the lock a part of the slide that grabs the rail with a cam action. Since you dont know how the customer will install let him drill the holes to attach to tunnel since he has to clear things like heat exchangers, hoses, tailight harnesses.....

For calculation sake I would use ~8-10 G's for load case of dynamic loading then add a FS of 2-3.

$nowMeansBroke · Nov 28, 2007

Thanks for all of the insight, I'm kind of confused by what you mean here though.

KWB said:
Use geometry to nest your parts on the bottom and at least two sides.

Are you saying to use maybe an L shaped bracket or something that will be able to have contact on the sides of the item too? This seems like a pretty interesting idea, I'm just trying to figure out what exactly you're talking about.

Thanks again.

SaberKitty · Nov 28, 2007

Can it be done profitably with a retail of $40?

snow_knight · Nov 28, 2007

design looks ok.. will definatly need some fine tune'n

All i have to say is your are very lucky you didnt have to take it with Karim Muchi... that guy blows.. dont know if he is still down there or not.... but Dolan is cool.. good luck with your project

KWB · Nov 29, 2007

$nowMeansBroke said:
Thanks for all of the insight, I'm kind of confused by what you mean here though.

Are you saying to use maybe an L shaped bracket or something that will be able to have contact on the sides of the item too? This seems like a pretty interesting idea, I'm just trying to figure out what exactly you're talking about.

Thanks again.

Basically yes-- think of a 9x13 cake pan with only two vertical walls. While it may not exactly center the load it would allow for all DOF to be reacted in shear/tension. Basically you would have three points of contact on the bottom, two on one side and one on the third. Minimum amounts to define threespace and also good for supporting to prevent overconstraint and highly flexible for whatever you want to set onto your pad.

Still you end up with a pedistal mount configuration, with proprietary accessorys you can envelop the rail and minimize moment from mounting surfaces.

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Opinions on engineering class project

$nowMeansBroke

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LEE

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CADman

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Barnes

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vmaxfrank

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$nowMeansBroke

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PistonBroke

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$nowMeansBroke

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Ice Cap

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