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Old 07-25-2016, 02:35 PM   #781
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You do know a bunch of people have already invented this wheel...right?

Such as...

RV Holding Tank Sensors - Get accurate grey and black holding tank monitor readings
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Old 07-25-2016, 05:01 PM   #782
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Well yeah, but... where's the fun in that?! In all honesty though I dislike the through-the-wall type sensor because of its potential to get dirty and fail (though Horst Miracle Probes claim to have overcome that) but especially because their resolution is so low. I get to know only that that tank is or isn't full; there isn't any indication between 1/2 or 2/3 full and overflowing. To be fair, there are some off-the-shelf capacitive types available too. All that I've seen are a combination of unreasonably expensive with little to no provision for integration with a larger monitoring and control system.

Quote:
Originally Posted by aaronsb View Post
The other way that I might go about this would require a lot of little wires, but might be fine as well. I was thinking of a 4067 16 channel analog multiplexer, and "listen" to the capactive levels of 16 individual patches on the tank.
I thought about an array of discrete level sensors as well, though my spin on it was to push the analog sensing down into each of the patches. With a chip along the lines of FDC1004 (or the cheapest little MCU with cap sense capability) an arbitrary chain of patches could be built to work like a shift register and be easily read out periodically. BOM cost is higher, but in a way it's simpler because there are fewer wires coming off the tank and the analog sense leads would be kept very short. If you build the PCB at oshpark I might order a few of 'em too.

If you want to get really extreme you could put sensors at both ends of the tank to improve sensing while not on level ground. Maybe even use it as your "level bubble" when parking, if the sensor accuracy is good enough.
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Old 07-25-2016, 05:42 PM   #783
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Nice drawing of the tank holders. All the weight is supported by the lower lip of the frame. It looks like with your design you are able to weld it all up and then angle it in between the frame rails. That is a great feature.
I would like the outer support brackets brackets to be a little steeper. For that an additional pipe could go above the frame rails. So in that case the potholes that will increase the forces by a factor of 2??.. just a guess... are not all concentrated on the lower lip of the frame.

You can pull your lower bearing member and my upper member together with all thread.

Nice built

Later J

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Old 07-25-2016, 05:44 PM   #784
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Yeah, but you have to drill holes in the tank.
Quote:
Originally Posted by Tango View Post
You do know a bunch of people have already invented this wheel...right?

Such as...

RV Holding Tank Sensors - Get accurate grey and black holding tank monitor readings
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Old 07-25-2016, 05:45 PM   #785
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I'm really glad someone else mentioned bubble level, because I thought about that and decided I'd look crazy if I mentioned it.

Quote:
Originally Posted by family wagon View Post
Well yeah, but... where's the fun in that?! In all honesty though I dislike the through-the-wall type sensor because of its potential to get dirty and fail (though Horst Miracle Probes claim to have overcome that) but especially because their resolution is so low. I get to know only that that tank is or isn't full; there isn't any indication between 1/2 or 2/3 full and overflowing. To be fair, there are some off-the-shelf capacitive types available too. All that I've seen are a combination of unreasonably expensive with little to no provision for integration with a larger monitoring and control system.


I thought about an array of discrete level sensors as well, though my spin on it was to push the analog sensing down into each of the patches. With a chip along the lines of FDC1004 (or the cheapest little MCU with cap sense capability) an arbitrary chain of patches could be built to work like a shift register and be easily read out periodically. BOM cost is higher, but in a way it's simpler because there are fewer wires coming off the tank and the analog sense leads would be kept very short. If you build the PCB at oshpark I might order a few of 'em too.

If you want to get really extreme you could put sensors at both ends of the tank to improve sensing while not on level ground. Maybe even use it as your "level bubble" when parking, if the sensor accuracy is good enough.
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Old 07-25-2016, 06:05 PM   #786
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Quote:
Originally Posted by aaronsb View Post
I got 4x of the 47 gallon plastic tanks on ebay. They're just sort of barely the wrong shape, but close enough that you can't beat the price. If they were about 3 inches shorter and wider to keep the same volume they would have been perfect. Instead, they don't fit under the frame rails without a fight.

I'm using the "no mans gap" between the tanks for the insulation and heater.
I really like the price, but in my case they don't fit well. I really want to use between rails space as much as possible, because it is not usable for something else.

I will most likely build my own tanks from plastic. I want to cascade them for "clean" grey water.

Also I am thinking about using small garberator after the toilet and have an option to pump out without collecting.
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Old 07-25-2016, 06:07 PM   #787
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Thanks for the feedback on the brackets.

Not shown is the massive steel walls of the luggage bay that wrap around the frame rails, so throwing something around the top of the frame rail would be desirable but pretty impractical.

The cross braces huck bolted to the frame web are located within a few inches of the spans for the brackets, and since the farthest fiber of the bracket spans are touching the webbing, the load will get distributed pretty well on that bottom flange.

Approximate max static load of the webbing, per side:

aft (3 tank end) 300 lbs
mid (between) 280 lbs
front (front tank end) 260 lbs

total of 1680 lbs

Double that for some sort of safety factor, and it's still within the realm of probably not going to break.

What I'd like to do is duct tape my phone to the floor and drive over some speed bumps at different speeds - that should give me some measure of vertical acceleration over time, and give me an idea of what sort of dynamic acceleration I'd be expecting of the tank bracket system.

The floor of the cradle is constructed with 1.5"x3" thick wall channel, and the angled bracing is 2"x.5" flat bar. Only some of the floor components will be welded together, most of the components will be grade 8 bolts through members.

Your call out on the lower frame lip gives me an idea - it would be pretty trivial to lay a second cross-channel on the top of the frame, and hang the verticals from both sets of cross-channels. That would distribute the load significantly, and provide a safety factor that would make sense.


Remember too, the general plan is to drive anywhere with only half the tanks full. The worst case solution is all 4 tanks full for some reason. (two are waste, two are fresh)


Quote:
Originally Posted by joeblack5 View Post
Nice drawing of the tank holders. All the weight is supported by the lower lip of the frame. It looks like with your design you are able to weld it all up and then angle it in between the frame rails. That is a great feature.
I would like the outer support brackets brackets to be a little steeper. For that an additional pipe could go above the frame rails. So in that case the potholes that will increase the forces by a factor of 2??.. just a guess... are not all concentrated on the lower lip of the frame.

You can pull your lower bearing member and my upper member together with all thread.

Nice built

Later J

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Old 07-25-2016, 06:14 PM   #788
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I used this type of clamps when I made support for my storage bay floor.
Cooper Crouse-Hinds 531SST Beam Clamp; 1-5/16 Inch, Stainless Steel

This is reticulasly expensive because of stainless, but you can get them galvanized just for a few dollars each.

I think I saw them at HD , but profecianal stores carry many types. Just Google steel beam clamps and get the idea. Also look at Unistrut. They are not expensive but very versatile and you know all the ratings exactly....
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Here is my conversion thread:
http://www.skoolie.net/forums/f11/98-bluebird-tc2000-conversion-2-feet-roof-raise-3-slideouts-9728.html
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Old 07-25-2016, 06:22 PM   #789
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This sounds a little "out there" but I think the space between the tanks would work fantastic for some lithium battery packs. Do you have access to weld your tanks from aluminum?

Do you mean garberator = garbage disposal? I saw someone had literally plumbed a garbage disposal to their waste tank to pump out the water and I thought it was brilliant.

Are you going with black tanks for toilets or the hippie dehydrating toilet? I want some sort of dehydrating toilet, but there's room in there for a black tank I suppose.


Quote:
Originally Posted by Vlad View Post
I really like the price, but in my case they don't fit well. I really want to use between rails space as much as possible, because it is not usable for something else.

I will most likely build my own tanks from plastic. I want to cascade them for "clean" grey water.

Also I am thinking about using small garberator after the toilet and have an option to pump out without collecting.
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Old 07-25-2016, 08:46 PM   #790
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Quote:
Originally Posted by aaronsb View Post
This sounds a little "out there" but I think the space between the tanks would work fantastic for some lithium battery packs. Do you have access to weld your tanks from aluminum?

Do you mean garberator = garbage disposal? I saw someone had literally plumbed a garbage disposal to their waste tank to pump out the water and I thought it was brilliant.

Are you going with black tanks for toilets or the hippie dehydrating toilet? I want some sort of dehydrating toilet, but there's room in there for a black tank I suppose.
I tried to find info about using aluminum tanks and stainless ones. Most people don't even recommend to use 316 stainless. I think aluminum is out of question.

It is not hard at all to build your own plastic tanks. I talked to someone who is making plastic water tanks for living. He told me the best material is not hdpe, like most tanks, but pp polypropylene. You can bend it using heated wire and you can weld it using plastic welder like one sold at HF.

Garberarator, you are right garbage disposal. I saw a very cool video how somebody hooked it up and it actually will pump uphill.

There is no way I will build hippie style toilet. I just mentioned it to my wife, her face expression was priceless.....
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