Lego Technic AWD "Go Anywhere" Vehicle

[DLuders]

"InItForTheGame" posted a

of a Lego Technic All-Wheel-Drive vehicle. It uses two differentials and is articulated to conform to the terrain. I could not find any pictures of the creation, but the video shows closeups of its construction.

For the experienced Trial Truck MOCcers (like Zblj, Atr, and Sariel), could you explain again why the use of differentials is a "bad thing" for trial trucks? It seems to work well for this MOC. As I recall, Zblj's 7-part Trial Truck Tips didn't discuss this aspect of a successful Trial Truck. Did I miss something?

[Silcantar]

Differentials are disadvantageous when one or more wheels are likely to lose contact with the ground, such as when offroading. For a 4wd vehicle driven by one motor with 3 differentials, only one wheel has to lose contact with the ground for that wheel to receive all power from the motor. This vehicle is helped in part by the fact that the front and rear wheels are driven by separate motors, so if one wheel loses contact, two wheels will continue to receive power.

Around 1:45 in the video, you'll see that one of the wheels loses contact with the ground, and the vehicle has to go back downhill until it is touching the ground again. In a truck trial, this would represent vital seconds lost in completing the course.

Trial trucks generally operate on ground loose and uneven enough that a differential is largely superfluous, even when turning, as the outside wheel can easily slip to catch up with the inside wheel.

I'm not a truck-trial-er, so the lack of differentials actually really bugs me, even if they are a disadvantage. It sort of decreases the realism and the theoretical functionality of the vehicle. If I ever build a trial truck, I will likely try to create some kind of automatic locking differential, which would combine the advantages of having a differential and not having one.

[Zerobricks]

Yeah differentials are badd offroad, because they allow wheels with less traction to get all the power, which leaves the wheel with traction no power to climb. Also his differentials witll break gears by such big wheels and because they carry maximum torque.

[Sariel]

It seems to work well for this MOC.

Articulated vehicles need differentials in all axles to turn properly. Without differentials, they couldn't turn in place and they would struggle to turn while driving.

[Conchas]

In this case it works pretty well because the generous ground clearance, the articulated steering and kind of pendular suspension, help to keep all the wheels on ground almost always (as wee can see from the video).

Also the battery box on top of the front axis help to keep contact on both front wheels.

As Silcantar mentioned, when all this failed and one wheel gets off ground we immediately see where the problem is.

[CP5670]

Yeah differentials are badd offroad, because they allow wheels with less traction to get all the power, which leaves the wheel with traction no power to climb. Also his differentials witll break gears by such big wheels and because they carry maximum torque.

Have you tried using a torsen differential like this? I don't know if they work well in an actual model, but they are used to mitigate this issue in real life.

[m4rc1n]

Have you tried using a torsen differential like this? I don't know if they work well in an actual model, but they are used to mitigate this issue in real life.

As you can see, this Torsen diff, is quite big, it's 11 studs wide, and for the polish truck trial competition, it'll be too big. The rules says, that the truck has to be in approximately 1:13 scale, so the truck is about 25 stud wide, depending of the choose you made. More than that, it is good if the truck has got reduction just before the wheel, so there is just no place for that kind of differential. As you can see, the rules of polish truck trial is quite restrictive, thus, the competition are very interesting. We've got very realistic looking trucks, and very creative constructors, like Emilus, or Atr. Personally, I don't use diff in my trial truck, and the Silcantar gives you the answer in his post :)

More than that, we ride on a quite loose terrain, so the difference of the specific wheel is not big deal

Edited September 30, 2010 by m4rc1n