trx-8

vypravcihubicka

New member
Being from the land of a big tradition of 8x8s I just had to do it

trx6 + trx4kit equals trx8 + huge amount of parts left for other builds

600px


first sketches
600px




I tried some kind of cantilever suspension in the back, using 2:1 ratio lasercut levers. Also shortened the wheelbase on the rear axles about 3cm.
More travel to the axles however caused I cannot use the original trx4 driveshafts they do not have enough angle and bite.

600px

600px

600px

on the front the frame from laser cut inox added
 
Last edited:

vypravcihubicka

New member
since I needed to revert the rotation on the first axles I added a small transmission from 20t and 18t traxxas pinion gears and Prusa 3d print for the tranny housing. This makes the first axle overdrive by 10% and it seems it helps with the turning radius quite a lot ( although the other three axles still have unlocked differentials)

600px

600px

600px

600px

600px


the steering on these pictures was the first system and was not good at all, not worth mentioning......
wheels are RC4WD Milspecs with 3d printed 2.2 beadlocks.
 

vypravcihubicka

New member
then I tried two servos with connected horns over linkage to get correct ratios for the steering angles. However it was having quite a lot play in itself and it repeated breaking in some spots
600px

600px

600px
 

vypravcihubicka

New member
then I tried one 15mm shaft turning horns of different lenghts for each axle. This has worked quite ok in terms of reliability, but I realized that the steering angles change quite a lot on the limits of travel, and steering gets quite "random". This probably happens more or less on every 3link axle but as there are two close to each other they "fight" and it is simply ugly to watch as well

600px

600px

600px
 

vypravcihubicka

New member
so I changed the steering again
to get exact/symmetrical geometry I made both front axles 4 link, with a kind of "independend" steering via mountainbike brake wires ( it is actually 5mm brake housing and 1,2mm shifting cable). Each axle has a wire loop over pulley of different diameter matching the different steering angle. All attached to 65kg.cm king size servo ( cheap and strong).
I have run only three batteries on this sofar but it seems reliable, super easy to adjust and working properly.
Btw. while googling for the smallest wire/housing possible (did not find anything smaller than mtb size) I stumbled upon Capo, which makes faux "hydraulic" steering set based on the same solution.
It is not most elegant solution designwise I know but there will be further updates. The servo sticks out but this will get hidden when the cabin and spare tire and all the technical stuff trucks have behind the cabin have.

600px

600px

600px
 

vypravcihubicka

New member
no, actually. I wanted to make both axles mechanically dependent, i.e. more or less defined relation of angles. I am not sure if it would also work with two servos - I guess the cheaper ones (which I tend to use) do not hold the setup correctly. The problem is generally that when you have one axle steering vehicle lots of inaccuracy is not visible nor important, because the car goes somehow to where you want in the end anyway. But with two axles close to each other this becomes a problem both visually and functionally
 
Top