pic: Wheel 4 V1.2

[Rion Atkinson]

Originally Posted by CraigHickman

Completely correct. My machinist was also able to use a single tool for the majority of the job, which greatly sped the process up.

Rion, when can we see the next version? I'm looking forward to seeing your progress!

I would love to give you another version. But I have gained no advice on which to change from this thread. I have made a slight change as adviced by RC to allow easier G Code via CAM. But other than that there have been no suggestions.

If you would like to see it you can find it here. Feel free to email me any suggestions you have.

Originally Posted by AdamHeard

Cough. Ermm. excuse me, other rude phrases...

Alan was correct, in that the small radius there doesn't really solve the problem Raul stated. If your spoke is too thing to handle the side load, a small radius really isn't going to fix the problem; and if that little bit makes the difference, your factor of safety is too low.

Please, try to learn to have a discussion on here without being rude and insulting people.

First. I would like to say that this could all be assumed as a huge lack of communication. While both sides are correct it seems that both have taken the defensive. I have not read either as rude; a little conceded maybe, but not rude. But I also do not see this going anywhere.

Second. His radii may help, but you are correct; they do not address the problem that Raul presented. It's because of the side forces that the wheel would have on it that I will not be making the wheel depth any smaller.


-Rion

EDIT: On the note of the additional radii on the side, should I put those on there our would it make the production process to slow? If I should put them, what degree?

[Jon Jack]

This comes from personal experience...

In 2008 we got 'too greedy' with our wheel design and made the spokes way too thin. I think each spoke was something like .167" thick.

While practicing between LA and Atlanta, our driver turned a corner and something shinny rolled off our robot. After finishing the lap I went to go an examine what came off our robot, only to find that the wheel hub was still on the robot, but the rest of the wheel was gone.

After looking at the rest of the wheels, I found that others were starting to fatigue as can be seen in this photo.

The problem was caused by side loading and how thin our cross sectional area was. When we were doing our pre-fabrication analysis using Cosmos, we only checked the compression strength and 'normal' direction loading on the spokes. In both cases, the wheel had a factor of safety of >2. After we began breaking wheels I did another analysis on the effects of side loading and found that our FoS was <1.

If you look at the picture I linked, all the wheels broke at almost exactly the same spot, which also happened to be the smallest cross section of the spoke.

For Atlanta, we made a new set of wheels that had a thicker spoke and took the weight hit since we had 8+ lbs to work with.

Yes, weight is an important factor, but you don't want to under-build your wheels and have them break in the middle of competition. There are other places you can save weight with out sacrificing the structural integrity of your wheels.

Alan is right, where the radii are at now only help in the 'normal' direction. When it comes to side loading, they don't do anything.

[AdamHeard]

Rion,

In a discussion such as this, most likely everyone has a point that is correct; this does not validate rude comments or the "I told you so!" attitude, especially when directed to some of the most respected (for good reason) mentors in FIRST.

My post was certainly immature, but I have a hard time letting things like that slide.



Yes, radii such as those are good, we do them on our wheels; they can be machined easily with a ball end mill. They certainly help make the part stronger and reduce failure at that joint. However, you can see in the picture's Jon linked that they had a radius, and thin spokes can still fail.

Raul was making a valid point, analyze what kinds of forces are on your wheels before you lighten the heck out of them. No one can say "1/4" thick spokes are strong enough" without knowing the floor surface, wheel tread, drive type, etc.

[Rion Atkinson]

Originally Posted by AdamHeard

Rion,

In a discussion such as this, most likely everyone has a point that is correct; this does not validate rude comments or the "I told you so!" attitude, especially when directed to some of the most respected (for good reason) mentors in FIRST.

My post was certainly immature, but I have a hard time letting things like that slide.



Yes, radii such as those are good, we do them on our wheels; they can be machined easily with a ball end mill. They certainly help make the part stronger and reduce failure at that joint. However, you can see in the picture's Jon linked that they had a radius, and thin spokes can still fail.

Raul was making a valid point, analyze what kinds of forces are on your wheels before you lighten the heck out of them. No one can say "1/4" thick spokes are strong enough" without knowing the floor surface, wheel tread, drive type, etc.

While you have a point (the "I told you so" attitude being wrong) I have dealt with stuff like this sense I have joined my robotics team. I guess everyone learns in different areas in different times. I do apologize for calling you out on this.

OK. Back on topic.

I honestly have no idea how to use the stress analysis on SolidWorks. Would anyone mind either looking over it for me or giving me a detailed walk through? Also. If I were to add the radii, what degree of a fillet should I put on them?

-Rion

[artdutra04]

Originally Posted by Formerly Famous

I honestly have no idea how to use the stress analysis on SolidWorks. Would anyone mind either looking over it for me or giving me a detailed walk through? Also. If I were to add the radii, what degree of a fillet should I put on them?

-Rion

Go to the tutorials under the Help menu; you can learn how to do simple normal and shear stress tests in under ten minutes.