A model of the Russian military truck- Ural 4320.
This model is a quite complicated model, I will talk about it a bit more further on.
The first prototype for this truck had only one gearbox, linked to all 3 axles by universal joints. That was the day the first U-joint broke :(. So I decided I must not use any universal joints to transfer power to the rear axles. And then the hard thinking began. I knew I had to place one of the two XL motors in the area of the rear axles, but the question was how. I thought about some options, such as connecting the motor on the in-facing side of the 2nd axle (like my rock crawler), attaching the motor from the upside of the axles, or attach a gearbox with a motor and a shifting mechanism somewhere over there. The last option seemed a little mad to me, but because I”m mad too I used it :) .
Now that was a complicated job. I had to stick that mechanism between the rear axles and yet not interfere their travel, I made it. Now because the rear axles have their own gearbox the front one needed one too, so I gave it one, identical to the rear one, that produce overall ratios of 1:3 and 1:9.
This truck has two kinds of suspensions a pendular for the front axles, and the rear axles are solid axles with a balance cart. The truck is not exceptionally pretty, but comparing to my other trucks its appearance is very detailed- The cabin even has interior!
By the time I finished the actual building I faced the problem of control. I set up a Power Functions regular IR connection and it worked just fine. But “just fine” is not enough. I usually drive my creations outdoors, and as you may know the sun messes a lot with IR. Because where I live we have plenty of sun, I decided to give up IR, and go with bluetooth. That means NXT. The new solution meant new problems to me. The ideal solution for me is to give each driving motor its own port (so it will have the maximum amount of power), give the steering motor one port and the 2 motors that controlled the shifting mechanisms one port as well. The thing was that the NXT brick has 3 motor ports and I needed 4. Now listen carefully, my solution was like this: I hooked one NXT motor to a PF switch that controls the 2 XL propulsion motors which are powered by a PF battery box. The other 2 functions have been controlled straight from the NXT.
To sum up, we got:
- Front steering
- Two 2 speeds gearboxes
- Full suspension
- Opening bonnet with a manual fake motor
- Bluetooth remote control via NXT