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Old 08-10-2021, 04:34 PM   #21
Bus Crazy
 
HamSkoolie's Avatar
 
Join Date: Jul 2021
Location: Southern Oregon
Posts: 1,607
Year: 1996
Coachwork: AmTran (Now Navistar)
Engine: DT444E (7.3L) International
Rated Cap: 31,800 pounds
Quote:
Originally Posted by LargeMargeInBaja View Post
Code might say '10-gauge for x feet to carry x amperage'.
I automatically go a size larger... in this example, I would spring for the bulk and weight of 8-gauge.
Why?
Our rig is constantly evolving, I have no way to predict future draws.
A good point and the larger wire will carry whatever load more efficiently (less resistance) resulting in fewer watts consumed for the work done by the circuit and less heat.


Quote:
Originally Posted by LargeMargeInBaja View Post
I tend to think vibrations of a vehicle warrant braided cable instead of solid such as Romex 12/2.

A minor ability to absorb flexing could be the difference between a cool outlet and an outlet warmed by resistance.
Romex only in AC circuits and THHN stranded would be better but not necessary provided proper design and installation.
Do you mean stranded or braided, there is a difference and while braided cable is usually superior to stranded it's increased cost isn't warranted for use in a mobile build.


Quote:
Originally Posted by LargeMargeInBaja View Post
I mentioned investing in heavier cable than Code requires.
That weight quickly accumulates... particularly outside the center-of-mass such as the photovoltaic system on a roof.
The center of mass, often referred to as the Center of Gravity of CG is a single point for a given mass. While in our buses it is going to be within the bus, it isn't necessarily so.


Quote:
Originally Posted by LargeMargeInBaja View Post
Concluding that thought, I have no way to prove this, but I think a diesel pusher concentrates an enormous mass outside the center-of-mass, and has the potential to radically affect handling of a vehicle in motion.
This is true but ALL mass except that at the EXACT point of the center of mass is "outside the center-of-mass". In the case of my bus, over 20,000 pounds of mass (when empty) was outside the center of mass before I started working on it.
When it comes to the Newton's law's:

"An object at rest remains at rest, and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force."
This applies equally to front, rear, and mid engine (yes there are mid engine buses, you do not want one) buses, the inertia is simply in a different location. Notice on rear engine buses that the rear axle is almost always very very close to the rear of the bus. This is to minimize weight behind the axle and assist in weight distribution by keeping the fulcrum as far to the rear as possible. You'll also notice that the front wheels are generally further back than a front engine flat nose bus. This utilizes the fulcrum of the front axle to put more weight on the front axle than were the wheels fully forward.

In front flat nose buses you'll notice the wheels are generally as far forward as engine and door location will allow. This is to place the fulcrum as far forward as possible.
Mid engines are strange critters to be avoided.
The whole purpose of locating the fulcrum of the axles is to BALANCE the weight distribution on the wheels for handling and other performance reasons but that rear diesel has no more affect than a front flat nose or a dog nose. It's just in a different place and the design must take the inertia of that mass into consideration in order to maintain proper weight and balance distribution an acceptable handling characteristics such as over or under steer, resistance to rollover, traction, etc.



Quote:
Originally Posted by LargeMargeInBaja View Post
And 'yes', weight as small as a few pounds of copper has an impact on vehicle handling, fuel mileage, and stopping ability.
True. However, a couple of pounds in a 20-30,000 pound system is going to be theoretical and un measurable.
Putting 200 gallons of fresh water (1666#), 1000# of solar panels, 1000# of decking, and 500# of support rails is SIGNIFICANT.
Keep liquids LOW and take fluid flow into consideration (baffled tanks are best and yet difficult to find).
Keep heavy items like batteries, generators, wood stoves, etc. as low as practical.
Consider left to right balance in your build plan with (In the US) the left side equal or slightly heavier than the right side (due to road crown).
As for the center of mass, you can calculate it from individual weights of each wheel position. The lower it is the better you will be.

If would be nice to know the weight distribution the bus was designed for but I have no idea how we'd find that other than in a specs manual or by weighing an actual bus. However, we can get an idea by looking at the weight distribution of our axle gross weights.

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We've done so much, for so long, with so little, we now do the impossible, overnight, with nothing. US Marines -- 6531, 3521. . . .Ret ASE brakes & elect. Ret (auto and aviation mech). Extra Class HAM, NAUI/PADI OpenWater diver
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