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RC models by Robert Holsting

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  Custom build flatbed, automatic / manual steering and ramps! Scale 1:14.

I need something to move crane components with, and something that my MAN can use for other purposes.
Since the MAN is a heavy hall truck, then something like a flatbed would be perfect.

Steering and ramps are servo operated with the option to enable some automation.


Color: Deep blue metallic: Tamiya TS19. (My favorite!)    Light grey: RAL 7012

  These are the guys that I need to transport - well, four of them anyway.
The biggest will sit on the crane it self with the two large lift cylinders and what-not, but the remaining four elements need to be transported separately, to keep total weight of the crane down when driving on non-flat surfaces.

The total weight of element 2, 3, 4 and 5 including all mechanics etc is more than 12kg!
My TLT axles on the crane has a limit, and that limit is breached if I was to drive the crane with everything fitted, and then experience a situation where not all axles support the weight.

That does happen on our model roads, because scaling things down are not always true to real life situations.

  At first I found this in my Liebherr brochure.
It would look great as a model, but a flatbed might be more versatile.

  - so when I found this, I knew what I wanted to transport my crane boom elements 2, 3, 4 and 5.

  First a plan on my trusted friend: The whiteboard!

  - followed up with a purchase: The Carson 3 axle Goldhofer, all steel, flatbed.

  - and three steered axles.

  This is the flatbed right out of the box. Not long enough, so I went and got my metal saw..

  MUCH better!
It is a funny feeling, cutting a brand new trailer, straight out of the box..

  Since I add an axle, I have to do another wheel well, and other details, in the white plastic used all over the place.

  Close-up of the wheel well, matching the other ones.

  One end closed.
Closing the ends look better, than just nothing - and it adds the stability that is lost when cutting it in half.

Note that the center beam is NOT bolted to the rear half, but slides inside the larger size around it.

  Note that the center beam is bolted on to the front half, and that the larger size around it only serves to align it with the rear half.

  I wanted to make it visible that the flatbed can be extended, so I added two narrow strips on the top on either side of the extension line.

  The extension is manual, and can be locked in 4 steps. I might automate the extension later, but not for now.

The center beam is a 15x15mm, running inside a 20x20mm that is fixed on the rear half - like a telescope setup.

  Three steered axles, and one of the original non-steered axles.

  First road test. The wire is the signal to the steering servo.

  - and now with the intended load: One of the crane book elements.

  Steering has several modes:
Mode: Full manual.
Note that the tractor is turning, while the flatbed is not.

  Mode: Full manual.
Note that the flatbed is turning, while the tractor is not.

In manual mode: The sterring has it's own controller knob, fully independant from tractor steering.

  Mode: Automatic.
Note that the flatbed trails the tractor.
(Channels mixed / copied via radio mix.)

  Mode: Automatic.
Note that the flatbed counter-steers the tractor.
(Channels mixed, and one reversed, via radio mix.)

  The US Dump truck got a little restless, so I gave it a tour around the house. :-)

  The flatbed accommodates a 40' container as well - cool!

And now back to the workshop - details and ramp automation is still pending.

  I had to make some brass for the ramps because they are simply too loose with the factory setup.
These brass plates also servo as a servo horn on each ramp.

  Close-up of the servo horn, right side.

  Note the holes that I have made in the back of the flatbed, so the servo horns can be connected to servoes under the floor.

  These are the servo rods, length are 60,5mm each.

  This is the supplied steering servo fastners, and it works fine.

  This is my ramp servo fastners that will go in either side.

All three servoes are Graupner DES 707 BB MG
(Digital, ball-bearings, metal gears. Torque at 6.0V, approx.: 150 N/cm)

  Plenty of space for these three power houses!

  Note the mounting through the "mud flap" and the rear of the trailer, holding the servo firmly in place.

  The two grey plastic guides have to be shortened a bit, but that causes no problems.

  It's painting time!

  After painting, the final assembly and adjustments.

  The upper side is covered with wood, painted in "teak" color.

  The finished result. The bed was painted grey, because it is a working area, and will get scratched.
The blue metallic would look too shiny here..

  UAT 1 ..
(User Acceptance Test)

  Close-up of the mechanics.

  Close-up of the mechanics.

Rear lamps are fitted with LED's, as are the license plate holder.

  - and that is pretty much it.

  Note that I had to reinvent the ramp unfolding system. The system from the factory works fine when operated by hand, but not when you add automation. Two steel wires solved the problems - not pretty, but it is acceptable given the alternatives.

  Ramps adjusted, and works!

  Chains added - got to have those!

  Compact state.

  Extended state.

  Note that the rear wall of the little bed on the nech has been removed..

  .. so the long elements fit!
Later I'll make some holders for the elements on my CNC, and mount those on the flatbed.

  Total length, fully extended:
Ramps up: 120cm
Ramps down: 152cm

Total length, not extended, ramps up: 91cm - weight 7,2kg

  Extension:
Max 29cm, in four steps.

  A few details and items.

  - and that is it.. project completed.