Videos of the UH-13PT

In anticipation, checkout these videos of the UH-13PT.

Trailer Brake Controller

As I was looking at trailers that were large enough for this project I realized that I was going to need a brake controller for my car.

Unfortunately Subaru was not accomidating enough to provide integrated brake controllers in my Outback.  The new Forester seems to have access for integrated brake controllers.  But on the recommendation of my dad I looked into the Max Brake controller.  See http://www.maxbrake.com/ for the product website.

The Max Brake controller mounted under my steering wheel.

Most other brake controllers are based on accelerometers, the more expensive ones are 3 axis mems gyors which learn their orientation, and the cheaper ones have historically been simple pendulums.  As the vehicle slows down, the brakes are applied on the trailer.  This concept has some significant downsides.  It has a bit of phase lag as the trailer brakes won't respond until the car has started slowing down.  And as I am going to be towing the trailer with my car and not a truck, the mass ratio between the car and trailer is even worse, making the emergency case worse.
The other similar solution is surge brakes.  These work by having a spring built into the tongue of the trailer and when the hitch pushes forward against the car the brakes are applied.  This happens when braking, or when backing up.  So there's a way to disable it for backing up hill.  And the surge brakes also have the same issue of a delayed response requiring the car to start slowing down before reacting.  And only reacting in relationship to how much the car is slowing down.

The acceleration based systems fail if the braking is improperly tuned.  In the case they are too powerful they will lead to oscillations as the trailer overbrakes at first, then slows down, stops braking, speeds up, overbrakes, stops braking, speeds up, ....  The same effect can happen with the accelerometer based brakes, though often not as pronounced.  And likewise if the gain is improperly set too low.  The trailer will just never brake as hard as you want.

In contract, the design of the Max Brake is to tap into the hydraulic brake line of the car, thus directly sensing the drivers braking command.  After calibrating the sensor to know what the pressure in the brake line is for full and zero braking, there is one knob to determine the ratio of trailer braking to car braking, such that for any amount of brake pressure you will have a repeatable trailer brake pressure.

The easiest way to see the value of this system is to understand how it overcomes the oscillating trailer issue.  If you brake gently at a constant force on the brake pedal,  the trailer will brake gently and constantly too.  Tuning the knob on the controller will adjust the ratio of vehicle braking to trailer braking, but they will both hold constant if the brake is constant.  Importantly this will work for both regular braking and emergency braking.  When the acceleration based systems are tuned well for normal driving it is hard to make sure that they respond proportionally to your desired braking in an emergency.  And it brakes down in the case that the vehicle starts losing traction, say if the trailer is to conservative in it's braking.

PS I did have an idiot cut me off when I was coming home from the dealership on I-5 and was very glad that the trailer brakes were super responsive.


Here are some pictures of my setup.  I bought the Max Brake controller and then had Kurt and Dorn's of Palo Alto install it because I didn't want to work on my brake lines without training/practice.  They were able install it in a few hours.

The Max Brake controller in context. 

The tee joint with pressure sensor attached to my brake line at the output of the master brake cylinder.   

The output of the Max Brake wired next to the trailer lights connector. 

Universal Hovercraft Kit Ordered!

So I ordered the Universal Hovercraft 13PT Twin Trainer kit today.  I chose it because it's the simplest full size kit.  It has all the parts I will need except for basic lumber, which I'll pick up at Home Depot.

I also upgraded to the finished propeller and fan so that I won't have to worry about balancing them myself.

Ordering today, they hope to finish the kit by the end of the week, and then it will got out by ground shipping.  So I hope to have it by the end of next week if all goes well.  Otherwise it'll be early the week afterwords.

Trailer Hitch

So to be able to pull a trailer you need a hitch.

I luckily saw the potential future need of a hitch when I got my car and it has a factory 1.25" receiver installed.

But on top of that you need to get the ball mount and ball.  I got a 2" ball and the highest lift I could find for the 1.25" receiver, which was only 4".

The trailer is level at 23" but with the 4" lift and my receiver height I'm only at 18".  It should work for towing but is not optimal.  I'll look around a little bit more for a larger drop ball mounts.  However they do appear hard to come by.

Trailer details and pictures

So the trailer I decided to buy was the Triton XT-168, (Manufacturer info page)

Of the statistics on the trailer, the most important ones were for me that it was:

• > 13.5' long for the hovercraft
• > 6.5' wide for the hovercraft
• < 2200 lbs so I can tow the 500 lb hovercraft behind my Subaru Outback with a 2700 lb trailer rating.  

Here are some pictures of the trailer now that it's light outside.

A front view of the trailer.

Here's a front quarter view.  You can see there's both a side door and a ramp in the front diagonal.

Opening the front ramp.

A view all the way through the rear ramp out the front.

Here's a side view with both ramps open.  You can see the two vents in the roof that I hope will keep me cool in the summer.

There's a nice recessed spare tire storage box under the floor.

Here's the tongue of the trailer.  It's well enough balanced that I can lift the front of the trailer by hand.

Here's a rear view of the trailer. It's amazingly wide. My whole Outback could fit inside easily, short of the v-nose.  And it's close to within the weight limit of the trailer.

Here's a peek underneath.  It's a simple but robust construction.

Here's the hitch all locked up.

The trailer has arrived!

So today I was able to go pick up the trailer inside which I'm planning to build and store the hovercraft.  Here's the picture I took when picking it up.  I'll take some more tomorrow in the daylight.

Hovercraft Cruising

Of course not everyone races hovercrafts.  There's also a sizable "cruising" community which use the hovercraft to explore lakes and waterways.

Now if you don't have a hovercraft in this estuary, you can end up like this:

For a sense of what hovercraft racing can be, check out this highlight reel from Poland.

The Hovercraft Museum

In my research I quickly came across the Hovercraft Museum in Hampshire.  It's a great resource for links, including clubs, kits, and current manufacturers.

They have a small photo album of their current displays, usually with a quick paragraph about the vessels, but not too much more.  And they're promising a new website in 2012, I hope that it will have more content about the historical vessels.  There's lots of stuff if you browse photos tagged at the museum, like these.

They have a lot of large vessels which are large enough to be seen from satellite imagery such as google maps.

Welcome

What sort of vehicle can drive on land and water just as well?  A hovercraft.  What sort of vehicle could do that and possibly be holonomic?  A hovercraft!

I've been intrigued by hovercrafts for a long time.  Now I'm finally going to do something about it.  My long term goal is to know enough to put together my own holonomic hovercraft design.  But to get to that point is going to be a long learning process.  

I plan to document the process here so that others interested in hovercrafts too can learn with me.  I have started this process by doing a lot of online research, and I hope that my postings will be helpful for the next person who gets a similar spark.