Tuesday 26 January 2010, by
See it online
This is my first 8x8 trial truck, but i think it’s worth to post :). It’s not yet finished, I plan to improve the rear suspension-axle-gearing, and also to make a better outlook (to suit "international" rules in that way).
I have built 3 TT-s during the last 2 years, and then i decided to make something bigger, with similar front axle i used in my hummer "TT".
My main aim was (just as before) to achieve maximum efficiency, decrease the amount of gearing, while making a drivetrain that is strong enough to stall the motors if the "hand of the God" (=me) block the wheels, without anything like this:
Great "spring distance" (not sure that’s the correct expr.) was also between my aims. As it is a TT the low center of gravity is also crucial, so i fixed the place for the RC unit in the middle, and as low as possible (This also makes easier the changing of the batteries)
The key to make the drivetrain strong, was to increase torque as close to the wheels as possible. I started building the truck from the front axle and suspension, which took a lot of time inspite of the fact, that i "stole it" from my Hummer; i had to improve it. On the following picture you can see 3 1:3 gearing in a compact house, and the first attempt for the suspension (which was a 4 link one).
As i finished the first prototype i realized, these links (and pins) are simply too weak to bear the forces from all directions during offroad, so I came up with a bit strange suspension system, which meets my requirements:
Three "Technic Suspension Steering Link 6L" are used. 2 connects with a pin to the axle, and "fixed" horizontally on the other end. The third one connects to another steering link, the other end of it can freely slide on the axle.
One motor drives one side, which helps the motors to work in balance. I mean eg. when the truck meets an obstacle the motors are loaded almost equally, which imo increases overall perfomace. While turning a little speed difference is also possible beetween the two sides, but i agree, it’s rather a truck with closed differential than with open:)...
OK these are just words and pictures, let’s see it working :)
Final ratio is: 1:45, and the outer output of the RC motors is used.
(The sticker on the top comes from the first Malug TT competition, I left it on that panel:))
I wondered, what happens if i double the amount of motors used for driving, so i simply added 1-1 motors for the sides and decreased the final ratio to 1:15, and i used the inner (faster) output of the motors. I also considered that I use 66 gears, 20 UJ-s, and if i play with it for long hours, i won’t have the gears and UJ-s to change them; so i put some greasing on it. The truck became heavyer : 3250 grams.
Fight against 3 chairs and a little snow action (note that 1 chair is on a smoother surface)
I’m not sure if i have used always the correct expressions, please feel free to correct, and of course to ask and leave comments:).
View online : Brickshelf: TT-4-Raba-H22