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RC models by Robert Holsting

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  Custom build flatbed, automatic microprocessor controlled steering! Scale 1:14.

The flatbed was constructed from the ground up, and only the axles were purchased as finished components.
Research on the web gave a few ideas and some inspiration, the rest came along the way.

Top features are the automatic microporcessor controlled steering, and the automated landing legs. This was the first time that software went into one of my models, but certainly not the last! Mastering the Atmega processors or similar, opens a world of options. More about this later..

Ramps, winch, and a complete set of lights are controlled via remote.             Note: Videos available here!

  The real size model that I leaned most towards, is this one.

Measurements of my model:
Length: 114cm
Width: 20cm
Height: 23,5cm.
Weight: 5,5kg.

  Initial planning.
This is when I realized that it would turn out quite large, which was good! I have a tank that needs moving, and the occasional 20kg excavators in the club.

  I wanted to read the angle between the trailer, and the tractor, so I needed to build something that would lock in to the saddle on the tractor, and decode the angle for the steering.
I also needed to read if the locking pin was open or locked, and feed that signal into the landing legs.

On with the thinking cap....

  This is what I came up with:
The king pin in the middle of the disk lock into the saddel as normal, the triangle matches the shape of the saddel so the disk cannot turn, and the optical detector within the triangle detects the locking pin.

  When mounted on the neck of the trailer, and test- fitted on the tractor, I can now detect the angle!

The king pin, the disk with the triangle, and a ball bearing is bolted together, and locked down!

  .. as you can see, the red indicator (here for illustration) does not turn, even though the trailer does.

We will return to the electronics in a little while...

  Next was the landing gear. A regular set of landing gear was rebuild, so the motor have a longer shaft.

  The landing gear goes on either side of the neck...

  ... and small micro switches controls the end points.

We will return to the electronics in a little while...

  Now it was time to build the neck, so I knew how much space I had for electronics and stuff.
Regular 1 & 2mm plastic plate was used for this. Pretty straight forward.
I wanted a look that gave the impression that parts could be removed, so 1 mm strips was glued on top of the 2mm base pieces in the corners etc.
Paint gave the final optical illution.

  This is where the battery will go, and there's also a little glimpse of the electronics bay in the middle.

  Little yellow side markings (2mm LED's) will go into the lower edge of the neck, and down both sides of the deck, all the way to the ramps in the back.

  Now on with the bed itself, first mounting the rails for the axles, and strength.
The little arms that stick out are the arms from the central steering boom, controlled by one servo at the back end.
This method ensures that all axles steer correctly with no further fuss.

Another option is to chain the axles, but then a faliure in any one place could (would?) disable all.

  The neck will click into place, and be bolted on.

  Same area from above.
I just love the shine of brass and aluminum...

  This is the cabinet that will hold the on / off, manual winch control (also controllable via remote), and the charge plug, all seen from below.
It's built in plastic, with a stong base of a 2mm alu angle. Built to last..

  Servos for ramps, and steering. The two ramp servos must turn in opposite direction, so a "servo reverser" goes on one of them.

It's funny.. plenty of space all over the place, and then all three servos MUST sit within the same, little area.. :-D
Just like children.

  With the basics done, it's time for some paint.
Some places will not be able to be painted later, so the time is now.

  The tail lights are a good example. Painting them prior to fitting let me get into all the little corners.
At this time all LED's are fitted as well.

  Close to final assembly!
Waiting 2-3 days for the automotive paint to cure fully, so I won't scratch it.

  Getting ready to lay the wooden floor.
The paint used for the wooden floor was actually some left-over paint from the fence towards the neighbor. (Pine-color, sprayed on.)
Thin, double sided tape (yellow squares) was used to secure the deck. I was considering epoxy, but I was afraid that because wood and metal would work differently in the heat / cold, the wood would break loose again.
Tape can stretch.. epoxy cannot.

  A while later, the floor was in place.
If you look closely, you can see the steering servo extrude up through the floor in the middle, at the back. It was later covered by a piece of deck plating.
I had to use a 15kg servo, so the height of the servo ended up to be slightly bigger than I had hoped.

  Notice the overlapping. Not two boards line up by the ends.
The two brass strips give a nice visual effect, breaking the wooden floor into segments.
The strips are actually used to bolt things from below into, so they are a critical part of the construction.

  The winch is bolted into a couple layers of aluminum, and will certainly not fall off!

The pulling power is about 2kg's @ 7,2 V.

  With all that done, it was time to return to the electronics.
First, the circuit controlling the landing gear needed a bit of adjusting. Initially it gave false reactions when in strong light, so an adjustment was in place!

With that done, steering was next.

  This is the 10K potentiometer that will go on top of the king pin, adn the bolt that will go from below, through the king pin and into the mechanism.

The two little black things are hexagon bolts, securing the king pin bolt.

  Here it's all mounted! You can see the disk and the triangle + optical detector in the mirror, laying on the table, and the 10K potentiometer mounted in a bracket over the (rotating) king pin.

  I know that real development boards can be bought for microprocessors, but all I need is somehow to solder wires in a "birds nest" for tests, development and a few LED's to indicate stuff. This home made device will do the trick, and it even holds an on-board power supply.
The board accepts both Atmega 8 and Atmega 32, depending on the project requirements. (I built a huge clock with Atmega32 on it too.)

The black box is a TinyUSB controller / programmer, available online, including drivers and all. (USA)

 

This is the circuit needed for the Atmega 8 to control a servo (steering). Adjusting endpoints, center-point, defining dead-band in the middle section ( + and - 6* in my case) so the flatbed does not react to lane corrections, are all done in software. It does not get any easier than that!

As a little treat I hereby offer my software, either for use or inspiration. Also: Check the next picture! Important info about the "Steering enable" swz.
Software: Click here (Remember to rename the file to main.c for your compiler.)
(No support, no liability blablabla..)


  End stop micro switches, and "Steering disable":
The schematics above show a switch called "Steering enabled" It's a micro switch that the landing gear pushes at the top position with a pin mounted in the landing gears moving parts. Why?
If steering was enabled when trying to catch the trailer, then the moving steering would cause the trailer to move, if the angle is different from when it was released, thus making it hard to catch the king pin.

  This is the circuit for the automated landing legs, including the diodes and endpoint switches.

Sencitivity can be adjusted by changing the 220K resistor, or by redefining the trigger-point at pin 2's two resistors.
Check out the datasheet for LM393 for the details.

(No support, no liability blablabla..)

  -and that's it!!

The license plate is actually my year of birth.. 1971 :-)

  The winch sits between the two work lights, which turns on by remote.

  The neck turned out ok, but I has to include a house for the potentiometer...
It's not a dog house.. really NOT...

  ... as you can see here.
This compartment holds all of the electronics, except the controller for the winch.

  A little peak under the neck, and the spiral cord for the revolving disk / king pin / triangle / optical detector.

  From the left: Charge plug, on / off switch, and the blue button for local, manual winch operation. (As an option to using the remote.)

  A little glance at some details, the spare wheel for the tractor.

(The flatbed has 24 wheels, surely it can make it home without one or two... thus no spare tire for the flatbed.)

  Steering is tracing great and it corners better than a small Fiat!

  Time for some real work! The Leopard 2A6 on the flatbed. Plenty of space, no need to fold things up, and what not...

I have since then pulled 26kg without any problems.. I am not sure where the limit is, but eaxh axle is rated to about 5-6 kg's, putting the max load limit to 30-36 kg's.

  Delivery accepted, project closed. :-)