Hello, I plan to build a car that would weight about 1Kg. I want the rear wheels to be motorized (likely with an XL motor that I'm going to order) and have shock absorbers. I wish there was a real soft axle hose with crosses at the tips but it seems the only solution is to use universal joints and I'm afraid that they quickly break. Any feedback on this ?

I don't really build Technic so I can't be sure. But if you are talking about the cross axels on a 1KG car I am sure they will break. Perhaps if the weight was lower and less load was needed they would break so easily. Of course you will want to talk to a Technic builder too.

Hello, I plan to build a car that would weight about 1Kg. I want the rear wheels to be motorized (likely with an XL motor that I'm going to order) and have shock absorbers. I wish there was a real soft axle hose with crosses at the tips but it seems the only solution is to use universal joints and I'm afraid that they quickly break. Any feedback on this ?

For a heavy car I recommend that you attach one motor to each wheel and suspend the lot on each side, leaving out transmission altogether.

I had conceived such a scheme for an 8x8 truck using the largest wheels from 8466 off-roader and one XL motor per wheel, though I might make it one medium PF motor per wheel for more speed if the power requirement is lower. The electrics would sort out any differential speed between wheels when cornering.

Standard LEGO axles and uni-joints just weren't made for power transmission. That's one reason why the first RC car with suspension used the 52192 motors rather than having a differential gear.

Remember that an XL motor can twist a 3M axle, so the shorter the axle the better, though it has to be at least 3M in order to go through a frame so you could attach each motor and wheel assembly to the suspension.

Mark

I wish there was a real soft axle hose with crosses at the tips

There is the old Znap flexible axle, but it's hard to come by these days and I don't know if it would be stronger than the universal joints anyway.

Hello, I plan to build a car that would weight about 1Kg. I want the rear wheels to be motorized (likely with an XL motor that I'm going to order) and have shock absorbers. I wish there was a real soft axle hose with crosses at the tips but it seems the only solution is to use universal joints and I'm afraid that they quickly break. Any feedback on this ?

You can always make your own u-joint. There are a number of examples on Brickshelf.

Otherwise you can devise something more like a CV joint by using the double bevel gears as joints. Since they can act as both spur and bevel gears, you can vary the angle between them. There's also the ball gear from the helicopter cyclic which was used on the 8880 wheels.

Really though, an open cruciform section has about the worst torsional strength imaginable. Add to that the fact that the axles are made of plastic and you have something which was really not designed to transmit high torque (hence the existence of the clutch gear). Even if the axle or u-joint doesn't break, you'll snap teeth off of gears.

Still, some people have made large scale powered cars. Check out this for example.

I built a very strong u-joint that I seen on one of crowkillers model. I think it was on his red mustang. It works great and is near impossible to break and is very small. That might help you

I built a very strong u-joint that I seen on one of crowkillers model. I think it was on his red mustang. It works great and is near impossible to break and is very small. That might help you

Do you have pictures ?

I believe this is the vehicle he's referring to.

http://www.brickshelf.com/cgi-bin/gallery.cgi?f=305058

Laurie

I believe this is the vehicle he's referring to.

I can't see a custom u-joint in this maze of beams, only the standard lego part.

As you can read from the replies, an xL-motor can snap the joint, but gear it up using a 2:1 gearing or higher and you are safe. The Motor doesn't loose much torque and should be strong enough to pull a 1kg model acceptably fast.

The vehicle Ed Diment and myself built for the Neo Classic Space website (L.U.R.C.H.) weighs about two kg. It uses universal joints in the drive, because it was driven through the front wheels and those were also used for steering.

You can see part of one in this picture:

All kinds of things failed on early versions, but never the universal joints. We put them through a fair bit of abuse without any problems. I have no experience with the newer three-long ones, though.

The vehicle is powered by an XL motor and it is geared down. We tried driving an early version of the vehicle without any gearing and as a result it was going so fast on its fat wheels that it was almost impossible to control. The motor certainly doesn't lack oomph (to use a scientific term ).

Cheers,

Ralph

It is in this picture here. He posted close up pics of it, but he must have deleted them. I ask him why he changed it, he said in his new model he made use of 3length joint that did not exist when he built the first car. He say that the original one looked funny, but I built it and it works super.

You could try a geared hub, that way the UJ transmits more speed and less torque:

Image from zblj's Brickshelf

The older 4L U-joints in some cases might break indeed, though on the other I have build a trialtruck in the past which had a lot of them in and weight around 3,5KG. It managed to cope with any obstacle putting a lot of force on the U-joints, but except for 1 none broke. The 12 tooth half bevel gears on the other hand did explode.

All in all for most situation the old 4L U-joints can take a lot before breaking and to be sure, you can always use the new 3L U-joints which is stronger. The only "failure" I've seen so far with the 3L U-joint, is the centerparts falling out, which is easily put together again.

Have a look at the 8880 Super car's suspension. Think it had 4 wheel drive with 4 wheel suspension. It didn't use the univarsal joints but I can't realy describe what it used. Like ball and socket type arrangement.

On UK ebay there's actually a full set of that sets suspension and steering system for sale - item 270409117184

The problem with those joints is that the wheel hub seems to rub against the white piece and creates some friction. This is the main reason the Super Car is hard to motorize. I think the joints only work with that particular wheel too.

The modern 8466/Ferrari CV joints don't have this issue but look no stronger than the usual U-joints.

The problem with those joints is that the wheel hub seems to rub against the white piece and creates some friction. This is the main reason the Super Car is hard to motorize. I think the joints only work with that particular wheel too.

The modern 8466/Ferrari CV joints don't have this issue but look no stronger than the usual U-joints.

The 8880 isn't too hard to motorize if you do it properly. The 8880 suspension/wheel hub parts work excellent even in driven vehicles and are quite popular amongst Lego Truck Trial competitors. The only disadvantage as you mentioned indeed, is that they can only be used in combination with the wheels of the 8880. Though there are to attach different wheels:

How well this actually works I'm not sure of as I have never tried it myself.

The images come from a site I came across a few years ago: http://onyx.malagraphixia.com/Sehr_Schnell...chnell_Main.htm

I remember seeing that site and picture before, now that you bring it up. In fact, I just tried building that setup and the axle stays in place surprisingly well with one gear. This would avoid the whole friction issue as well. The only problem is that the wheel would jut out significantly and make the whole vehicle wider.

The newer RC and PF XL motors can probably handle the Super Car. It's been a while since I looked into it. There were several Lugnet threads on that issue back in the day and I don't think anyone found a good solution, but we only had the basic gray motors back then.

I just tried it as well and indeed it's quite sturdy. It does combine pretty well with the larger wheels, like the power-puller wheels as well as the regular racing tires that are used for the F1 1:8 technic car for instance. Using smaller wheels does give some offset resulting in needing a wide area for turning the wheels. On the other hand, I don't think that it differs much from the newer wheel hubs to be honest.