Reinforcing an axle for a tri-star wheel?

[clinton10]

I built a tri-star wheel arrangement (Technic Example, Wikipedia Entry) that I'm really pleased with.

Here is the mechanism in progress:

The wheel assembly, in progress

Tri-Star Wheel Reverse.jpg (42.37 KiB) Viewed 7292 times

And here is a complete wheel.

The completed tri-star wheel assembly

Tri-Star Wheel Front.jpg (51.11 KiB) Viewed 7292 times

As you can see, it is, in effect, a very large wheel. I built two of them for use in an NXT to go through an obstacle course. Unfortunately, the wheels require a lot of torque. In other obstacle-course-overcoming robots, I've bent the teeth on gears; this time, I snapped an axle extender.

Is there any way for me to build a thicker, stronger axle or reinforce an axle, or build something that is similar to an axle (perhaps out of beams) so as to not break pieces? (Yes, I understand that increases stress in other parts of the system.) I can see many ways in which this would be difficult (wouldn't fit into standard gears or wheels, wouldn't go through holes in the studs) and yet, I'd rather not abandon the idea.

[doc222]

By just what can be seen of the design; The center 40T gear must be the power too the tristar if so its an overdrive since it touches/drives gesr that are smaller. This is some of the trouble. Other issues will be friction . that is alot of non compounding gears. Back in the Nxtsasy post we had a talk about the Tristar.

Yes you can make an axle stronger but it may add to much to it to be functional. If the connection of axles is breaking one way to make the joint stronger is to use something other than the axle joiner. many ways to do tis using other parts but ALL make it widder as well.

I think a design that uses less parts will be better than using the one example shown. Back a year or so ago, i was working on this design my self( My favorit movie vehicle, Landmaster(tristar)). I tested a design that works very well, wont break parts, wont over load motors and is geared 1:1 to the wheels and the bot would go over steps, dirt and the only thing that would break it was my dog, seems them three wheels on each axle is more than he can stand:), but i have much smaller tires, one thing about tristar is the fact you need 12 tires all the same size. I like the ones you are using though they maybe a bit large for this. But well worth trying it if you have enough of them.

A few pics of my test back then.

[clinton10]

Interesting. That's a great design.

I knew that the speed increase due to the 40t gear going into a 24t gear was a problem, and the 8t gears are the weakest links, but didn't think that was my largest problem. It looks like I'll need to get some additional 40t gears.

I really like how you used the bent liftarms to make you tri-star arrangement. I figured that as they weren't 120 degrees, they'd not be suitable.

I was also planning on just having tri-star wheels at the front (I have 7 of those large tires) and something for the robot to drag along behind itself. I don't know that I've got 12 of any sort of medium-sized wheels, but I ought to be able to use different wheels on the front and back to good effect.

What happens if one does not power the rear wheels?

[dimastero]

What happens if one does not power the rear wheels?

I'm aware this post is over a month old, but I just stumbled upon it now. I've made a few robots without rear power, and the biggest problem seems to be weight distribution. When the robot tries to climb stuff (in my case, at least), it get keeps on getting its back part stuck (especially the part that actually supports the robot, like a wheel or something), as the tilt made most of the weight go back, making the front wheels either slip or lift off the ground, making the robot look pathetically like a turtle (again, that's in my case :-p). I think the best way to avoid that happening is to make the rear a bit higher than the hight of the robot's front + the maximum amount it climbs at once (if the robot' is balanced), lowering the wheels compared to the robot's main part. That usually works for me. The only problem is that it makes the bots look kinda silly...

Hope that helps,
DiMastero