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Rescue Truck makeover
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A loving mechanical and visual makeover of a favorite set, the sleek and elegant 8x2x6 Rescue Truck (8454) -- now sleeker and redder than ever, but still prepared to hose down anything that needs or deserves it at a moment's notice.
About this creation
Please feel free to look over the images and skip the verbiage.

For years, I'd admired the exterior lines of the LEGO® Rescue Truck (set 8454, 2003) from the box cover photo alone, and my friend and frequent building buddy Shawn Kelley knew it.

One December day in 2013, Shawn showed up with a big grin on his face and a box and big bag in hand. When he pulled a fully assembled Rescue Truck out of the box, I figured he was about to show me a score (he's a big collector) that he knew I'd want to see, but the next thing out of his mouth was, "Merry Christmas."

After getting up off the floor and thanking him profusely, I told him I couldn't accept such a valuable gift, but he would have none of it. Then he opened the bag, and out came the original box and instructions. I was speechless.



Now able to read the box top, I learned that the "rescue truck" is really a low-profile airport fire and rescue vehicle. Its body shape was even cooler in hand than I'd imagined from the box cover photo, and it had a nice heft and solid feel.



The gas dampers and cam-over mounts on the rear hatch and gull-wing side doors gave them a very pleasing manual action. Better yet, 3 steered axles with convergent geometry gave it a remarkably small turning radius for its length. I also picked up some good building tricks from examining its simple but sturdy studless frame.

The rescue truck was begging to be motorized, and I wanted to show off its sleek, elegant lines by eliminating some of the more distracting visual elements. As usual, one thing led to another.

Before long, the following changes had been made:
  • Replaced fake engine in rear compartment with L motor for propulsion and revised drivetrain accordingly.
  • Motorized steering with PF stepper motor placed in middle compartment (between side doors).
  • Reworked water cannon linkages to make room for an IR receiver peeking through the roof above them.
  • Replaced cockpit seats with AAA battery box (nowhere else to put it).
  • Reinforced or reconfigured internal structure here and there.
  • Increased overall width by 2 LU for an even more pleasing frontal aspect ratio by pushing side panels outward.
  • Relocated and revised side door mounts to allow damper to operate as before.
  • Filled in roof wherever possible for a cleaner look.
  • Eliminated extraneous exterior colors and decals.
  • Removed black and white wheel covers (had a better use for them) and switched to dark gray wheels.
Below is the resulting rescue truck make-over. I'm still patting myself on the back for motorizing it, because the make-over is more fun to drive than any other model I own -- and that's saying something. I owe Shawn a big one.

On this page:
Photos
Specifications




Photos











My gussied-up rescue truck is long, low, sleek, and very, very red. I honored the original palette of red, black, and both old grays but replaced non-red exterior parts with red ones wherever possible. Most of the many the gaps in the roof were filled in with red parts as well.

The make-over lost some utility truck cache in the process, but it's still got a water cannon dangling over the cab, ready to hose down anything that needs or deserves it at a moment's notice. The black IR receiver port peeks up above the roofline between the cannon and the red knob that operates it manually.



The rescue truck is based on an 8x2x6 platform, meaning that of its 8 wheels, 2 are driven, and 6 are steered. As in a rear wheel drive car (4x2x2), none of its wheels are both driven and steered. (The latest Mars rover, Curiosity, has a 6x6x4 platform, with all 6 wheels driven, and all 4 corner wheels steered.)

The long rescue truck owes its ability to make smooth, tight turns to its 6-wheel steering with convergent geometry. The latter specifies steering arm lengths according to axle position along the wheelbase such that all axles on the same side converge on the same point when extended toward the inside of the turn.

Also noteworthy in the photo above are the added strings of straight axle connectors running below the curved body panels. These reinforce the fore-to-aft continuity of the bodywork lines and add definition to the wheel wells. It's tempting to add rear glass to the hatch, but I've found nothing suitable so far.



Top view for scale. The light-colored floor tiles were 305 mm (12 in) squares before the corner cuts.





Opening one of the long gull-wing side doors a little allows the pressure stored in the trans-blue gas damper to open it the rest of the way. (The limited length of the damper allows only one side door to be open at a time.) Revising and relocating the cam-over side door mounts eliminated the need for the sliding side door lock included in the original instructions.



Another gas damper with a cam-over mounting holds the rear hatch open or closed as desired. Below it is the business end of the L motor used for propulsion.



The police-like trans-blue "emergency light" originally operating the rear hatch has become a fixture. A smaller red ball hidden behind it now works the hatch. The light bar was a gratuitous add-on.





Pushing the side panels outward by one LU on each side by various means widened the make-over by 2 LU relative to the original.

With overall height and length unchanged, the result was a reduced frontal aspect ratio (height over width) that I found more appealing and also more in keeping with the airport utility truck profiles I'm used to seeing. By eliminating some of the original offsets in the body design, this change also produced more flowing lines from front to rear.

The inward lean of the wheels evident in these photos is a tolerable side-effect my serendipitous wiggly axle traction control system. The rescue truck had no suspension originally, and with 6 steered wheels, I wasn't eager to add any.

Nor did I want to mess with its convergent steering geometry, and that meant harnessing the new propulsion motor to the same wheels previously connected to the fake engine -- namely, the 3rd pair from the front. Retaining the original drivetrain's differential was also a goal.



Given the location of the drive wheels along the wheelbase, this combination turned out to be a recipe for traction loss, as one or both drive wheels would frequently be lifted off the ground when any more forward wheel was raised -- e.g., by rolling up onto the edge of an area rug. A motorized make-over so easily disabled was not what I had in mind.



Wiggly axle traction control is ridiculously simple: You just allow the steered, non-driven axles to wiggle a bit in their steering arms. (With the rescue truck's simple 1 LU-wide steering arms, that's exactly what they were inclined to do anyway.)

On encountering a bump, the leading wheels then deflect upward a bit before lifting the chassis. That brief delay is often all the drive wheels need to retain traction through the bump. It's not a complete cure, but the rescue truck got stuck a lot less often after wiggly axle traction control went (back) into effect.

Ah, the wages of habitual thinking! As an axle support fanatic, I could only have come by this trick accidentally. Before even installing the motor, I replaced the original steered axles with 5.5L stopped axles and jacketed them with half bushes, as shown on the left.

This treatment reduces wiggle and bending in poorly supported cantilevered wheel axles. In the rescue truck's case, however, it worked too well. Now I get the necessary axle wiggle by using pin joiners to shim the wheels out to their proper positions, as shown on the right.



While we're looking at the undercarriage, here's the rear end. Part of the propulsion L motor shows above the frame rails. Below is the drivetrain, little changed from the original.



The undercarriage in full. Note the convergent-steering arm length changes along the wheelbase.



Undercarriage view with the steered axles at full lock.

To see how well the rescue truck's steered axles converge, first note the following facts:
  • All steered axles use the same rack and 8-tooth pinion in both the original set and the MOC.
  • Rack pitch is 3.25 mm/tooth.
  • The steering system accommodates the stepper motor's full range of rotation (-90° to +-90°).
  • Turning an 8-tooth pinion 90° moves each rack by 2 teeth, giving each rack the same throw of X = 2 * 3.25 = 6.5 mm at full lock.
  • Numbering the axles 1 through 4 from front to rear, the steered axles are located Y1 = 188, Y2 = 124, and Y4 = -68 mm away from the non-steered axle at Y3 = 0.
  • The steering arms measure A1 = 16 mm, A2 = 24 mm and A4 = 32 mm center to center.
  • A protractor confirms the steering angles θ1 = 24°, θ2 = 16°, and θ4 = 11.7° calculated from the constant rack throw of X = 6.5 mm and the simple trig relation θi = arcsin(X / Ai).
It's not hard to show that the other steered axles will converge with the front axle (i = 1) if

θi = arctan[tan(θ1) Yi / Y1]

for i = 2 and i = 4 -- i.e., if θ2 = 16.3° and θ4 = -9.1°.

Comparing these values to the actual steering angles given above shows near-perfect convergence for the 2nd axle. However, θ4 is 2.6° too large.

It would take a good bit of rebuilding to change either Y4 or A4, especially in this MOC, but if A4 could be changed without changing Y4, it would have to be lengthened to 41.0 mm to bring the 4th (rearmost) axle into perfect convergence.

After doing the math, I can look back at the photo above and convince myself that the 4th axle looks oversteered, but I certainly never noticed it beforehand. Nor do the rear wheels struggle visibly in tight turns.



A closer look at the L motor and the upper part of the propulsion gear train, which yields a net reduction of 2:1. This combination gives the make-over a better than average top speed for a PF vehicle.

To my mind, the L motor's the most versatile motor LEGO® has ever produced. In fact, it's become my motor of choice for all but the hardest-working of PF models -- especially land vehicles and speedboats. Its high torque for size and broad power band are evident in its torque vs. speed curve, and the mounting opportunities it provides far exceed those of any other LEGO® motor. Compared to the M motor, it's a bit of a power hog, but you get what you pay for.



A glimpse of the PF stepper motor used for steering in the middle compartment between the side doors.



IMO, the red flexible axles defining the cab roof and windshield do a much better job of that than the original silver pearl axles and further strengthen the fore-to-aft lines. Creating a place to hide the AAA battery box now replacing the front seats would have required a major redesign.




Specifications

Overall dimensions:366 x 160 x 105 mm (LxWxH) excluding IR receiver port and water cannon
Frontal aspect ratio:0.66 (height/width)
Lateral aspect ratio:0.29 (height/length)
Overall weight:1.14 kg (2.5 lb)
Construction:Paneled and studless exterior with largely studless chassis and panel supports
Basis:LEGO® Rescue Truck set (8454-1, released in 2003)
Scale:Undetermined
Gas dampers:2
Platform:8x6x2
Propulsion:L motor driving 3rd axle from front (not steered) with 2:1 reduction
Suspension:None
Motors:2 in all -- 1 L for propulsion, 1 PF stepper for steering
Lights:3 LED pairs -- 1 each for headlights, tail lights, and front floodlights
IR receiver connections:2 -- 1 for each motor
Electrical power:7.2V AAA battery box with rechargeable NiMH cells
Modified LEGO® parts:None
Non-LEGO® parts:None
Credits:Entirely original make-over of a classic Technic set
Thanks:To Shawn for this most generous and memorable gift





Comments

 I made it 
  May 3, 2017
Quoting Craig Howarth At last someone nuttier than me. I love your work, it's fantastic. I'm going to need some time to go through your creations and pinch your ideas :) Do you make jet engine noises whilst secretly playing Mars research drone attack? Just checking that I'm not the only one.
Very kind, Craig! Yes, I make all kinds of noises whilst playing with my MOCs. Just not when the wife's around. And no, you're not the only one -- especially not on MOCpages. Feel free to pinch away!
 I like it 
  April 26, 2017
At last someone nuttier than me. I love your work, it's fantastic. I'm going to need some time to go through your creations and pinch your ideas :) Do you make jet engine noises whilst secretly playing Mars research drone attack? Just checking that I'm not the only one.
 I made it 
  April 3, 2016
Quoting Barış BAYER Very very nice and smooth work. I like it too much. Can you, please, share the plans?
Thank you! Unfortunately, there are no plans, and it would take too much of my time and effort to create them. However, you can probably download the instructions for the original set from lego.com and use the photos from there.
  March 31, 2016
Very very nice and smooth work. I like it too much. Can you, please, share the plans?
 I made it 
  January 23, 2015
Quoting Nick Barrett You've made a thorough job of this beauty and it'll now be tons of fun! Also, I appreciate your verbiage - it's interesting and I learned a thing or two.
Thanks, Nick. I'm glad you found at least some of the verbiage useful.
 I like it 
  January 23, 2015
You've made a thorough job of this beauty and it'll now be tons of fun! Also, I appreciate your verbiage - it's interesting and I learned a thing or two.
 I made it 
  January 7, 2015
Quoting miki miki wow :o
Thanks, miki miki.
 I made it 
  January 7, 2015
Quoting Romy British very nice ! Excellent idea, nice shape, absolutely awesome !
Thanks, Romy. TLG deserves most of the credit for the shape. I just spiffed it up here and there.
 I like it 
  January 7, 2015
wow :o
 I like it 
  January 4, 2015
very nice ! Excellent idea, nice shape, absolutely awesome !
 I like it 
  August 24, 2014
Hi, wonderful concept is here of the Rescue Truck makeover. I would suggest we partner in our efforts to create a breakthrough green aerodynamic self-sufficient green powered rescue vehicle, please see my patent app and let me know how much we are complimenting each other’s design. Thank you, Rus: https://sites.google.com/site/texasinventip/
 I like it 
  March 4, 2014
Excellent job!! Love the technics!! 5/5 8-)
  March 2, 2014
Hey Jeremy, in answer to your question of who Syd Mead is, in short, he is the reason that YOUR designs look like they do. He was the designer for Blade Runner, Tron, Elysium, Aliens and countless other movies with a futuristic vehicle in it. He has been the primary influence of pretty much anything of a realistically futuristic design. I would guarantee that this original set was a direct descendant of his illustrations. Google his images, you will be impressed. (Sorry, my work computer won't allow me to paste a link.) Enjoy! I'm actually excited for your new introduction into his vision, it is life altering even though I'm certain that you'll recognize some of his work. BTW check out Michael Hritz in Mocpages. Similarly wonderful stuff!
  March 2, 2014
Fantastic tuck! You copied the shape of the real trucks very well!
 I made it 
  February 28, 2014
Quoting matt rowntRee Just way too cool! I always wanted that set, the design was very Syd Mead and futuristically utilitarian, like your snow cat. I could picture something like this patrolling across a lunar terrain in my brain. Now that it's motorized, I want one even more. Cool reimagining and an even cooler friend to drop that off for you. Outstanding!
Matt, Thanks once again for the kind words. Two things: (i) Who's Syd Mead? Sounds like I might like him or his work. (ii) The original set came in at under 700 parts, none of them particularly expensive or rare. If you're not dead-set on a box and printed instructions, and if the instructions are available for download from the LEGO® Customer Service site, recreating the model itself from BrickLink parts could conceivably be a lot cheaper than buying a set.
Jeremy McCreary
 I like it 
Matt Bace
  February 27, 2014
I always liked the original set (finally managed to pick one up on E-barf a few years ago). Your modifications to it are spectacular. I'd run out and buy one of these immediately if it were an official LEGO set. Great job!
 I like it 
  February 27, 2014
great story, it looks straight out of a thunderbirds episode! super design!
 I like it 
  February 27, 2014
Very rough 'n' tumble....Good for a nice day trundling OVER the forest.
 I like it 
  February 27, 2014
Just excellent! Very clever. Good work!
  February 27, 2014
Great MOC. Terrific functions, very well done.
  February 27, 2014
Forgot to mention, being a kid from the 70's, the set and now this, reminded me of a Saturday morning show called Ark 2. It was painful (not sure I'd recommend looking it up), but the RV was sweet.
 I like it 
  February 27, 2014
Just way too cool! I always wanted that set, the design was very Syd Mead and futuristically utilitarian, like your snow cat. I could picture something like this patrolling across a lunar terrain in my brain. Now that it's motorized, I want one even more. Cool reimagining and an even cooler friend to drop that off for you. Outstanding!
 
By Jeremy McCreary
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