Wednesday, January 2, 2019

Gas can mount on top of spare tire

Transporting the gas can for the generator is a real pain.  It's only a gallon of gas, but it smells bad and it gets in the way.  We have been carrying it in a small crate in the cargo area of the truck, for lack of a better alternative.  There is no room on the tongue of the trailer, and there was no other place to put it.

So I figured that the spare tire is on the back of the trailer, quite securely -- maybe there is a way to piggyback off the spare somehow?

My first job was to check the bolts mounting the spare, which is on the back wall of the trailer.  I discovered the bolts were loose (!), and the mount was supported by little tee nuts inside the trailer, which were all stripped.  I think that the original design of this trailer was for light duty, which is not the way we treat this trailer -- we take it off-road (slowly) and on long trips at highway speeds on California's roughest freeways.  (I'm lookin' right at you, I-5.)

So I upgraded the bolts mounting the spare -- instead of quarter inch ordinary steel bolts into tee nuts with no washers, they are now three-eighths stainless steel with wide fender washers inside and out, into massive lock nuts, all anchored with quarter inch steel plates on the inside of the trailer, in order to spread the load over as many square inches as possible.  Now, instead of having the spare fall off, the whole back wall will give way at once.  (Joke.) 

This is what the upgraded beefy steel plates look like, on the inside of the back wall:




OK.  The spare is secure.  Next, how to mount the gas can on top of the spare?  The goals are safety, lack of vibration, and ease of use, in that order.  Even with the reinforced bolts, the spare still vibrates in response to an impact:




Over time, vibration can lead to materials fatigue and failure.  So the gas can mount, ideally, should dampen that vibration.

Here is what I came up with, in summary (with details to follow below): using the bolts from the spare tire mount as an anchor, I extended two half inch threaded rods up to the level of the rim of the tire.  I then mounted a horizontal platform on those two vertical rods.  A heavy milk crate is bolted to that platform.  The gas can goes in the milk crate.

Here is what the finished product looks like:




And now, the component steps.  This is the cross-bar anchored to the bolts supporting the spare tire mount -- I drilled holes in the angle bracket with my drill press to fit the bolts, and you can see the holes in the ends that will accept the vertical rods:



Here are the vertical rods rising from the cross-bar:



The platform will slide over those rods.  Note that there are pairs of nuts, tightly jammed together with lock washers, that will support one side of the platform.

Here is the spare tire on its mounting bracket, with the rods extending upward:



Here is the platform, mounted on the rods and resting on the top of the spare tire -- notice that on top of the platform there are nuts and washers holding the platform rigidly in place:



Here is a closer shot of the platform:



In that shot, at the very back of the platform, you can see the edge of an angle bracket extending across the back side.  The angle bracket is bolted to the platform -- the heads of the bolts are recessed:



This is a shot from underneath the platform, showing the angle bracket:



(By the way, if the components look distinctly un-glamorous, that's because this was all made from spare parts and pieces stashed in the corners of my workshop.)

Once I had the platform assembled, I put a piece of thin plywood inside the crate to sandwich the bottom of the crate, using countersunk wood screws -- the screws go through the crate and into the platform:



This milk crate is very sturdy -- no chance of materials failure.  Inside the crate, I built a foam "nest" to hold the gas can securely on all sides, using (of course) scraps of foam, including old purple "pool noodles:"



I knew from past painful experience that if a plastic gas can is subject to chafing for a long time, it will wear through.  So no hard surfaces are in contact with the gas can.  This is a shot of the gas can in its little nest:


Note, by the way, that the nozzle of the gas can is pointed inward.  Obviously, in order to add fuel, I loosen the collar and rotate the nozzle 180 degrees.

This is a side view of the crate and the gas can on top of the tire:



Notice the straps coming down from the crate and around the tire -- that is a ratchet strap.  By strapping the crate to the tire and anchoring the crate (on the platform) to the upright rods, the whole assembly vibrates much less than it did with just the tire on the mount.  Although it is hard to see in this shot, the straps are twisted to cut down on vibration due to the wind at freeway speeds.

This is a closer shot of the gas can in the crate:



You can see a piece of thick vinyl tubing extending across the crate and through the handle of the gas can, preventing it from bumping up and down while on the road.  Also, notice the bungee cord around the perimeter -- it is also designed to reduce the vibration of the ratchet straps.


The whole thing is very easy to install and remove.  To install, the platform drops down onto the rods, and I tighten the nuts.  Then the ratchet strap goes around the tire and the crate.  To remove, just loosen the ratchet strap, loosen the nuts on top of the platform, spin them up and off the rods, and then lift the platform off of the rods.

If we feel the need to lock the gas can in place, that will be easy to do with a combination bike cable lock.

That's it -- a lot of detail for a fairly small project.  But the design issues were more interesting than the fabrication process, which was pretty straightforward.


Wednesday, June 20, 2018

Aluminum replacement for broken T handle on holding tank valve rod

On a recent trip, part of the plastic T handle on my black tank valve rod snapped off while we were dumping the tank.  After a little research, I discovered that the T handle was internally threaded and screws right onto the end of the valve rod -- very convenient!

So I took a piece of half-inch thick aluminum scrap and used a hacksaw to cut a replacement handle.  I then shaped it with a flat file and then cleaned up all of the rough edges with a belt sander.

(I know what you are thinking -- why not just buy a new plastic handle?  I could, but I no longer trust those handles not to break at a crucial moment.  I wanted a heavy duty handle.)

Next, I drilled a 15/64 inch hole in the center of the piece, starting with an eighth inch bit, then a 3/15, and finally a 15/64 bit.  (Don't use a quarter inch bit -- the cutting threads on the tap will have nothing to cut if the hole is too big.)  I then used a quarter-inch 20 pitch tap in order to create internal threads in that hole, to match the threads on the end of the rod.

I screwed the replacement handle onto the rod, holding back on the rod with a vice grips so I could get it very tight.  The end of the threaded part of the rod projected out from the backside of the replacement handle by about 3/8 of an inch.  I put a lock nut onto that little stub and tightened it, so that the new handle will not unscrew from the rod.

Here are two views of the finished product.  This is a three-quarter end view:


And this is a side view:



Thursday, January 4, 2018

Insulating pad on window in the door: monofilament holds it in place


We often camp in pretty cold conditions – subfreezing but not sub-zero.  On a recent winter trip, we realized that the frosted window inset into the trailer door was losing a lot of heat.  So when I got home, I rigged up a way to hold a foam insulating pad on the inside of that window.  I think that other folks who camp in cold weather might find this useful.

As I do on our other windows, I used foam flooring material (from Costco), which comes in interlocking panels (about 2 feet square), cut down to fit the window opening.  The foam is about a half inch thick and is fairly stiff.  The window in our trailer's door was about 21 inches by 15 inches.  (Actually, I measured it in millimeters to give myself the illusion of precision.)  I cut the pad to size with a box cutter:


The next issue is how to hold the pad in place?  I thought about Velcro or magnets (my best friends) but decided to string four strands of monofilament fishing line (10 lb. test, I think) across the window to contain the pad.  Here is a shot of the pad on the door:




And this is a close-up of one of the monofilament cross-strings:



In order to create the cross-strings, I first took out a screw (one at a time!) and stuck one end of the string into the hole:



(By the way, please excuse the greasy fingers -- that's what my hands look like on a "garage day.")

I then screwed the screw back into the hole, trapping the end of the monofilament:



After tightening that screw, I removed the screw on the opposite side of the frame.  I cut the monofilament to be about 3/4 of an inch too long and then stuck that end of the line into the screw hole.  As I tightened the screw, it tightened the monofilament, taking up the slack.

In order to install the insulating pad, just slip one end under the lowest string and slide it up into place.  Remove it by sliding it down.  We store it under one of the dinette cushions -- a little extra padding never hurt anything.

Sunday, December 31, 2017

Wooden/Magnetic "Door Halfway-Open" Holder

This is a device to hold the door open halfway in breezy conditions. (It will not work in a high wind, but it works most of the time.)  We need to hold the door open when we are cooking, in order to ventilate the trailer.  We often do not want to open the door all the way -- too cold!  So this does the job without letting in too much cold air.

It is just a curved piece of oak lath (steam bent), with strong magnets at each end.  (I made an earlier version of this out of metal -- it was clunky and hard to deploy.)  It's curved in order to approximate the arc of the door jamb as it swings open -- a straight piece of wood would not do the job. (I tried it already.)

The magnets are on opposite sides of the lath.  One magnet sticks to the strike plate on the door frame, and the other sticks to the metal plate on the door that surrounds the bolt.  The magnets are taken from old computer hard drives.  The mounting plates already had screw holes, but I enlarged them slightly.

Here is the curved lath:


This shows how the magnets are attached to the lath.  The screws are very short -- about a quarter inch.  Note the green tape -- the ends are color-coded for convenience:


This is the inside end, which makes contact at the strike plate on the door frame -- note the red tape:


This is a view of the holder from the inside of the trailer:


And this is a view of the holder from the outside:


When not in use, the holder sticks to a small metal plate on the wall of the trailer, just inside the door.

Sunday, November 20, 2016

A Lighter Dinette Table (Baltic Birch Ply Instead of MDF and Formica)

The stock dinette table weighed a lot -- I think around 30 pounds.  Very awkward to lift when making the bed at night!  So I fabricated a lighter version, using half-inch Baltic Birch plywood.  I finished it with three coats of a wipe-on polyurethane.  We've been using it for over a year, and it has held up well.  It's about half as heavy.

Here is what it looks like when set up for dining:





This is an overview (underview?) of the underside:




And this is a close-up of the socket -- I glued a circular pad of plywood under the table and then screwed the socket into the pad, so that the screws would not come through the tabletop:




Tuesday, November 1, 2016

How to test the working capacity of the batteries

I have two group 31 12V marine deep cycle batteries, which supposedly have a total capacity of 110 amp hours.  In the real world, that means that they have a theoretical working capacity of only 55 amp hours, since I am told that it is not good to draw the battery down below a 50 percent state of charge.  When the measured voltage gets down to 12.1, that's a 50 percent state of charge.

So I wanted to see if I really have 55 amp hours available.  That information is useful for a couple of different reasons: first, if I do have that much available, that tells me that my usual battery maintenance routines are adequate.  If I don't, I have to do something different.  And this reading provides me with a baseline, so that I can tell when the batteries are starting to get old.  Finally, if there is a material difference between my two batteries, that would be interesting, since they were purchased at exactly the same time and have been used in exactly the same way.

(As you'll see below, the results were not what I was expecting.  Hint: this story turns out well.)

My overall plan was to hook up a lamp and then to see how long it took to draw the battery down to roughly 12.1.

I started with a fully charged battery  (which reads 12.9 V when it comes off the charger) and then let it rest for a day, so that the initial reading was 12.7 volts. 

I then hooked up a 60 watt incandescent bulb, plugged into a small inverter, which was plugged into a "cigarette lighter socket" adapter, which has alligator clips that go to the battery terminals.  (If you don't have one of those adapters, they are really handy when you want to hook a 12 V appliance directly to a battery.)  I then used my multimeter to find out how much current the bulb and the inverter were drawing, which was 6.1 amps.

(If you already know how to measure the amount of current that a device is using, skip this paragraph.)  Put the red (positive) multimeter plug into the "10 amp" socket on the front of the multimeter.  Turn the multimeter on to the 10 amp setting. It should read "zero."  With the lamp still plugged into the adapter, unhook the cigarette lighter adapter's black alligator clip from the negative terminal of the battery.  Touch the multimeter's black lead to the negative terminal.  Touch the multimeter's red lead to the unhooked black alligator clip on the cigarette lighter adapter.  The meter will display the amperage.

I left the light on for two hours, thus consuming 12.2 amp hours. I unplugged the light and let the battery rest before taking a reading.  I was told that it had to rest for two hours to settle down.  But I discovered that after a half hour of rest, the voltage had plateaued and did not change.  So for the rest of the experiment, I let the light run for two hours, followed by a half hour of rest, at which point I measured the voltage and then plugged the light in again.
Here are the results in a crude graphical format:


Volts



















12.7









12.6
     x








12.5

     x







12.4


     x






12.3



    x





12.2




    x




12.1





























Time            2hr      4hr          6hr          8hr       10hr      

So this means that after ten hours of actual run-time (consuming 61 amp hours), the battery got down to 12.2 volts, i.e., with 60 percent of capacity still remaining.  By extrapolating from this straight-line graph, it looks like I could have gone two more hours, for a total working capacity of 67 amp hours.

That is a lot better than the 55 amp hours of working capacity than I was expecting!

I did this experiment twice, once with each battery, and got exactly the same results.  This tells me that this wasn't a fluke.

I am not sure how it is possible that my batteries are outperforming their rated capacity, but I'm not complaining.  This won't change my consumption patterns when we are camping – we are very careful about electricity.  But this is encouraging news, and it gives me a baseline for subsequent comparisons.


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