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Tatra Dakar Truck

September 28th, 2016 Leave a comment Go to comments

Tatra Dakar TruckModel of a Dakar Truck based on Tatra T815 4×4. Features drive, steering, full suspension and custom stickers.

Datasheet:

Completion date: 27/09/2016
Power: electric (Power Functions)
Dimensions: length 37 studs / width 16 studs / height 24 studs
Weight: 1.273 kg
Suspension: front – double wishbone independent /rear – live axle
Propulsion: 2 x LEGO RC motor geared 1:1 from the faster output
Motors: 2 x LEGO RC motor, 1 x PF Servo

I’m a big fan of the Lego lime green color, so when I came across photos of a Tatra T815 4×4 Dakar truck in a beautiful lime/black livery, I just had to build it. It was also a good opportunity to test the performance of Lego RC motors when powered through SBricks.

The model was built at small scale, as low weight was my priority. It was propelled by two hard-coupled Lego RC motors whose faster outputs were used as the rear axle. The two motors were mounted on a ball joint, effectively creating a live axle rear suspension. In the middle of the chassis were two 8878 Lego batteries with a pair of Lego LEDs connected to each – this way the truck’s headlights acted as indicators of which batteries were turned on or off. On top of the LEDs’ plugs – to avoid adding more wires – were the SBricks, one per each battery. Between the batteries was a PF Servo motor controlling the front axle which used standard double wishbone independent suspension.

The body was built with just a few plates/tiles panels and it looked too tall because of the increased suspension travel. As the video demonstrates, the truck looked realistic when the suspension was pushed down – this is because the body was correctly scaled, but was sitting higher above the wheels than in the original truck. This was the inevitable result of using soft suspension with long travel. Another result were problems with stability – even though all heavy elements were placed very low in the chassis and the upper body was very light, the truck had a tendency to roll over when cornering at full speed. I was able to reduce this tendency by using harder shock absorbers in the front suspension and by decreasing the steering lock (not physically – I have simply limited it in the SBrick software), but it was still there. The truck cornered perfectly well if the speed was decreased – and this is understandable, seeing as the top speed of 12 km/h in a 19.5:1 scale model is equivalent to 234 km/h in a full-size truck.

I was pretty happy with the model because it performed very well and it was fun to drive. But at the same time it was pretty challenging to control and it made me appreciate the advantages of lower and wider vehicles that remain stable at high speeds.

Work in progress photos:

IMG_5792.JPG IMG_5796.JPG IMG_5809.JPG IMG_5968.JPG

Photos:

01.JPG 02.JPG 03.JPG 04.jpg 05.JPG 06.JPG 07.JPG 08.JPG 09.JPG 10.JPG IMG_5987.JPG IMG_5988.JPG IMG_5999.JPG IMG_6006.JPG IMG_6010.JPG IMG_6012.JPG IMG_6017.JPG IMG_6021.JPG IMG_6038.JPG IMG_6067.JPG IMG_6076.JPG original1.jpg original2.jpg original3.jpg original-t815.jpg

Video:

Media coverage:

Hobby Media (Italian), The Awesomer, The Lego Car Blog

Categories: Trucks Tags: , , ,
  1. Sariel
    October 12th, 2016 at 01:29 | #1

    @Technic Dragon
    Of course I’ve used that steering system. Multiple times.

  2. Technic Dragon
    October 12th, 2016 at 00:36 | #2

    I am PF XL motor by the way.

    I see you’ve never made any models using the 42021/42043 steering system, or the hard-to-use colors from the 42048 and 42050 sets. Maybe…

  3. Sariel
    October 7th, 2016 at 22:40 | #3

    @Tobias Stanisfugl
    But the two motors aren’t really independent. They’re hard-coupled.

  4. Tobias Stanisfugl
    October 7th, 2016 at 21:20 | #4

    Dear Sariel
    Nice design in this very colour I like too. This one shows once more, that it makes sense to install the biggest motors possible, or to strive for relatively small vehicles, all to better power/size.
    Regarding tipping over:
    – Studded bodies always are relatively heavy
    – You could easily lower the batteries at least one step downwards, without deceasing ground clearance, and mount them sideways eventually, to furtherly lower the c.o.g..
    – Why not designing a side stabilizator for the axle(s)?

    Always keep in mind that there is a tiny effect on the vehicle’s dynamics when cornering due to the small friction modulation there happens while the load changes, when using independent
    motors for each wheel. With electrical motors, it even matters if the motors are supplied independently or if they are electrically connected in parallel, since then the load change alters the current distribution to the two motors because of their impedance change. This is of course not the case in your model, since you use independent supplies to each motor.

    Long supension travel is meant to be used cross-country, but you show no such performance playing around on tarmac. How is it there?

    Best Regards Tobias Stanisfugl

  5. Sariel
    October 5th, 2016 at 17:41 | #5

    @Lorenzo
    I print them at Copy General.

  6. Lorenzo
    October 5th, 2016 at 15:28 | #6

    Hi Sariel, I wonder how you manage to make the stickers for your creations since they look amazing. Do you print them yourself using some special equipment? Greetings from Italy.

  7. Sariel
    October 2nd, 2016 at 21:48 | #7

    @sohibil
    Well, truth is I’ve built the chassis long before deciding on Tatra body.

  8. sohibil
    October 2nd, 2016 at 21:39 | #8

    You just made my day. Too bad you didn’t make the suspension with independent half-axles like real Tatra. This guy pulled off some succesful although slightly crude attempts http://www.kostky.org/forum/index.php?topic=49933.0

  9. Sariel
    October 1st, 2016 at 13:25 | #9

    @PF XL motor
    Maybe someday.

  10. PF XL motor
    September 30th, 2016 at 02:47 | #10

    Why not make another record breaker with 2 rc units?

  11. Jhoro
    September 28th, 2016 at 22:07 | #11

    Wonderful job again! I guess that you will need to publish a new book on building techniques which allow such a clean and nice finishing. I love the level of detail!

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