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Old 03-28-2010, 12:50 PM   #57
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If we consider what happens when a vehicle w/ a shock hits a bump, it is true that the force is somewhat higher on the initial reaction ... but the shock helps prevent the entire trailer from bouncing up and down several times after in reaction. Here's a graph on what various amounts of shock damping do to a step function input (which is like a bump in the road):



The interesting thing about shocks (ignoring gas shocks) is that the force they exert is proportional to the speed of their compression or extension.

Rubber torsion axles provide damping as well, intrinsically, because rubber has hysteresis: unlike steel springs, compression and expanding rubber absorbs significant amounts of energy (which is why tires get warm when driving):



Regular leaf springs do provide a little damping; the leaves rub together and create friction. This is actually counterproductive in terms of ride quality, and back when cars had leaf springs, placing greased cheesecloth between the leaves of the springs helped the car react more supplely to the road....

Whether or not a trailer w/ a rubber torsion axle needs shocks is an interesting question; I would imagine that depends a great deal on the characteristics of the rubber, number of axles, etc. If someone were to travel a section of rough road w/ an accelerometer-equipped trailer w/ and w/o shocks installed, much might be learned about the necessity of shock absorbers on Airstreams. Accelerometers used to hard to find outside a lab, but modern solid state versions are in IPhones, etc... there may be IPhone applications suitable for this already.
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Old 03-28-2010, 01:42 PM   #58
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They learn't you well where you're from

Quote:
Originally Posted by barts View Post
.. Here's a graph on what ... because rubber has hysteresis: unlike steel ... travel a section of rough road w/ an accelerometer-equipped trailer ...

Accelerometers used to hard to find outside a lab, but modern solid state versions are in IPhones, etc... there may be IPhone applications suitable for this already.
The last sentence is doubtful.

Who do you think your audience is? The people around here that already understood a damping function have already drawn their conclusion on the viability of shock absorbers on an Airstream.

Since you posted no conclusion, you may want to direct readers to the wiki(s) from which your statements were derived so all inclined to can understand everything involved.

Tom
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Old 03-28-2010, 05:24 PM   #59
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A further flogging of the proverbial deceased equine

The ground finally dried out enough around the camper so that I could crawl underneath and get a couple of pictures. Looks like you were correct, we (or more precisely, Ron) welded those arms much closer in to the frame than the factory did with yours. There's still a bit of cant, but not too bad. I should think that you can cut those arms off and move them inward without too much trouble (Of course, I'm assuming that you have, or know somebody that has, the right equipment to do so). This is the curbside rear wheel.

I have not read Atlas Shrugged but am very familiar with the basic thesis of the book. Given current events, the concept of Producers, Looters and Moochers seems to have a lot applicability to reality, doesn't it?

Jim
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Old 03-29-2010, 01:14 AM   #60
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Quote:
Originally Posted by TomW View Post
The last sentence is doubtful.
A minute or two w/ google returns:

Robota Softwarehouse - iPhone AcceleroLog - View accelerometer graphs and log data with your iPhone


Quote:
Who do you think your audience is? The people around here that already understood a damping function have already drawn their conclusion on the viability of shock absorbers on an Airstream.

Since you posted no conclusion, you may want to direct readers to the wiki(s) from which your statements were derived so all inclined to can understand everything involved.
I was hoping to make things a little clearer as to why shocks might be a good idea... but since I haven't taken any data (we're still refurbishing our Airstream) I wasn't going to come out and say "Yes, use shocks" or "No, they don't help much". I don't know how much force the shocks generate, how they're valved, etc. The fact that the same shock appears to be used on all Airstreams regardless of weight seems to indicate that they're not critical in this application.

For those interested in some technical links only tangentially related to the topic but having some handy pictures:
Second Order Dynamics - WolfWikis
ValveTypesSelection - ControlsWiki

- Bart
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Old 03-29-2010, 06:35 AM   #61
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Bart, What I believe Tom was saying without being blunt enough is that no matter how much you say, people have their minds made up about these axles. Never have I seen a more derisive topic discussed. When ever the WBCCI debate gets too heavy, switch over to an axle thread and you will be brought right back down a bit.
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Old 03-29-2010, 07:48 AM   #62
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auto-morph...

..some threads have an auto-morph-into-pissin-match mode...any one with the word "axle" in the title..

..quite entertaining, though, much more so than watching paint dry....
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Old 03-29-2010, 08:12 AM   #63
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Quote:
Originally Posted by barts View Post

For those interested in some technical links only tangentially related to the topic but having some handy pictures:
Second Order Dynamics - WolfWikis
ValveTypesSelection - ControlsWiki

- Bart
Those links brought back memories; neigh, flashbacks of my early engineering training. I really never liked dynamics much in the beginning. It turned out that I took them too early. I'd not had the required math classes prior. Once I had those the advance vibrations classes were a snap. Boy how I struggled early on though.
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Old 03-29-2010, 05:31 PM   #64
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Decent accelerometers cost serious bucks

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... Accelerometers used to hard to find outside a lab, but modern solid state versions are in IPhones, etc... there may be IPhone applications suitable for this already. .
To which I said "doubtful". "Suitable" is the keyword here.

Quote:
Originally Posted by barts
A minute or two w/ google returns: [something that at face value appears to fit the bill]
I invite you to strap an iPhone to the floor with the given app enabled. My first thought is that it will not have the sensitivity required for any reasonable analysis.

My second thought is that it will not have the sensitivity required for any reasonable analysis.

Since I don't have an iPhone, and subsequently do not know its capability, I will PayPal you $20 if you can provide a graph of data in 10 millisecond increments. Any decent lab can provide the same data real-time.

Tom
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Old 03-29-2010, 05:46 PM   #65
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With what I've read from Barts in the short time he's been here, I think you best get your $20 out and get some postage on it.


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My first thought is that it will not have the sensitivity required for any reasonable analysis.

My second thought is that it will not have the sensitivity required for any reasonable analysis.Tom
It sounds like BOTH your glasses are half empty.

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Old 03-30-2010, 01:18 PM   #66
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but both them glasses are shaken not stirred....
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