andythenorth

Can you fit any more flotation devices under it? Air tanks? More tyres? Cheat with plastic bottles?

Neat. I've been wondering about similar use for this part http://www.bricklink.com/catalogItem.asp?P=x136 It's used for the rear wheels on Spider Trike and has good flex in one axis. http://www.bricklink.com/catalogItemPic.asp?S=76014-1

Post some pictures when you have some progress

Up on the en-GB shop (scroll down). http://shop.lego.com...TECHNIC-ByTheme

4 XL is overkill You will either: 1. lose traction, with the wheels spinning (can be fixed with more weight above the drive axles, e.g. batteries or such) 2. if you can maintain traction, but you have a large enough load to stall the truck, the torque of the XLs will just destroy the drive train, most likely the 12t bevel gears in the diff. If the trailing load isn't very heavy (and I would guess 10-20KGs as 'heavy' in this context), then there is less chance of stalling out and destroying the drive train. But it's still overkill If you try and balance two XLs on either side of a diff (in theory this sounds good and gives variable speed), then the motors destroy the bevel gears in a matter of minutes.

Move the motors down and inline with the wheels. One will go in front of the lead axle, the other goes either between the rear and lead axle, or behind the rear axle (which might be too long). You can move motors further away, but this needs more transmission parts, which are a weak point. You could also try the L motors. L motors are not nearly as powerful as XL but they are still pretty good. They are longer, but not as wide, so might fit better to your chassis.

This truck has 1 XL motor per rear axle, and 1 XL for the front 2 axles (so 3 XL in total). The wheels are a little larger than the ones you're using. It uses 2x AA battery boxes, positioned over the rear axles for weight. Rear axles have diff locks. It will: - pull a 15KG child on a scooter + a load of toys on a rough slate floor - push a kitchen chair around a smooth wood floor - climb a 5cm vertical obstacle (with the diff locks in) Hope that's useful guidance

As the others said, two XL. I asked about the tyres because it's a good guide to the size of the vehicle. For the size you're using 2 XLs on double-drive tandems should work well. On smooth level ground you won't gain much by going to a tri-drive. Doesn't really matter if you use one motor per axle independently, or both motors are connected together. The more gears you have, the lower the efficiency of the drive train though.

Do you want to haul on level ground, or on rough terrain / places where wheels might slip? What tyres are you using? You might want to consider 2 XL motors. There is such a thing as too much torque though :) I'd power both rear axles, if nothing else it distributes the torque across more parts, means less chance of twisting axles, breaking gears etc.

I will get slated for this, but I really like 8070. It's really playable and fun. My two year old loves it too. My cousin had 8880, I hate the look of it, and the functions seemed fragile and fiddly. Each to their own etc.

What kind of terrain are you using this on? What you've built is a torque-limiter, not a torque-multiplier In lower-friction situations, applying the full torque to a wheel can cause it to break away and spin. In this case a lower torque will maintain traction. It's the same theory as driving a car in higher gears on snow.

Compressing the spring is parasitic - it requires force from the input axle. For a single axle, with a direct motor drive, the diversion of force into compressing the spring would reduce the force transmitted to the spur gear. For a set-up with a differential, I am not good enough at physics to figure out the overall split of torque between the two axles

I see no conflict of interest. I have a well-used Bricklink account.

Thanks. The newer small turntable also seems to be insanely strong. I've tried to pull one apart by hand, can't split it. Going to try using that instead

Try parts with the larger hubs, e.g. portal axles, or the hubs from the F1 car, or older steering hub parts. Works well.

Hmm. I'm using a large turntable as the roll joint in the center of the chassis. http://www.bricklink....asp?P=48452cx1 Problem: the truck pulls the turntable apart easily. Ideas for reinforcing it, or alternative solutions for roll joint? Maybe sandwich the large turntable and a small one, with a liftarm through the centre to retain the two sides? [

I am pretty certain Technic is going away. Kids these days don't want to build stuff. They just play video games, unlike the 1980s or 1990s. I think it will be gone within 9 months. I would buy a lot now.

I have random bags and boxes of unsorted parts. My kids (2 and 4) just dive in and build stuff with it.

Is the B-Model a trencher? http://commons.wikim...el_Trencher.jpg Russian trencher crossing river... https://www.youtube.com/watch?v=7k7YTvgsk3M

I am going to build a small truck next. It's a break from this monstrosity http://www.eurobricks.com/forum/index.php?showtopic=95488entry1899079 It won't be as small as yours

What's the steering like without diffs? Does it want to keep going in a straight line? Do you get a lot of windup in the axles?

http://www.bricklink...Item.asp?P=x346 Not a good picture, but you can just about see one used for the diff-lock here.

Nice. Small trucks are the way forward

Got steering in. Needs 2 LAs, both on same side. Tried one on each side, they bind. The XL is overkill and drives through the clutches constantly, also slow. A single M is too gutless for this, and as for L...I've run out (8 in the chassis). Although the turning circle is eventually tight, the steering performance is dreadful because the Power Puller wheels are so resistant to side-scrubbing. So it's slow, and twists up the chassis unless the wheels are also rotating (i.e. driving forwards or backwards). Kind of expected, the Commander has same issue with fewer wheels.. Still, if you want to turn you'd better block out some time in your diary. Also the chassis has a swivel (roll) joint with the large turntable. Currently 3KG. With ~2000mAh NiMH, 12 batteries are lasting about an hour. I'll probably add 2 more battery boxes, 1 per receiver. Currently on 3x v2 receivers and a v1 receiver. It stalls out right about where you'd want it to, any more and it would tear something up.