Let's Make Robots!

mounting wheels

Hi guys. Im really puzzled on how to mount the wheels for my micromouse. 


a guy did so, and many do the same http://www.micromouseonline.com/sites/default/files/wp-content/uploads/2009/10/IMG_4278-full.jpg but I don't know how to. Any Ideas? 




Just to make it more clear. Im confused on how to wheel is attached to the aluminium piece. Is there a special name for this so that i can research on it. I have no idea how to. I know how the aluminium piece is attached. Also .. what is the diameter for an m3 screw? hehe. 

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I'm going to go out on a limb and say that a M3 screw is probably 3mm (Three millimeters -or- 3/1000 of a meter).

As I said, the wheel is screwed on. There is a screw going through the center of the wheel and a lock nut is threaded on to the (non-head) end of the screw. In the case of the picture you provided, most likely the aluminum has been tapped as to give more rigidity to the screw and to avoid post-loading (bending of the screw upward when the weight of the robot is set on the wheels). The nut you see is a nylon lock nut and acts like a jam-nut when tightened against the aluminum. Again, the aluminum is probably tapped so it is as if you have 2 nuts, backed into each other, to create a "lock nut". --This "locking" is over-and-above the locking provided by the nylon insert in the nut itself. This is probably a bit of overkill however, if you think of the bolt (really now, an axle) as a lever, the nylon lock nut, being longer than a standard nut, will provide more support over the length of the bolt, thus moving the "moment" or "fulcrum" and strengthing the overall assembly. To avoid "lash" or lateral movement of the wheel itself on the bolt, I would assume there is probably a spacer of some kind between the wheel and the aluminum angle-iron. This spacer (in the States) is called a spacer, standoff, sleeve, bushing or bearing. Now, the tention of the bolt can be quite important. Too little and you will increase lash, the extreme case allowing the wheel to move so much that the gears themselves fall out of plane and no longer mesh. Too much and the rotation of the wheel will be restricted. I am not sure if the builder of this robot used the mic/install/remove/remic method to determine this tention or if he used a torque wrench. If a torque wrench was used, I would assume he used one with a 1/4" drive (the smaller one) and a "pointer" style one. I am not sure of a model of "clicker" type torque wrenches that is accurate down to the very small amount of torque that would have been needed for this installation. Also, he may have tested the restance to rotation of the wheel itself as he tightened the nut and bolt to determine the proper specs.

Now as I said before, it seems that the aluminum is tapped. If so, one should be careful with any of the above methods of measuring torque on this bolt as the secondary lock nut may affect the total torque on the wheel when it is applied. My suggestion is to check before and after this lock nut is installed to be sure nothing was thrown out of spec.

I think that's it. If you follow the above intructions/ suggestions, you should have no problems.

Thanks Chris for that nice informative reply. I think i understand it now. I am very poor for these kinds of things. Thanks alot again .

Upon closer inspection, the rivets are not rivits. The are simply screws as well. It seems the aluminum has been tapped and the mounting screws are threading into it.

As a matter of fact, I can even see some bluing on the aluminum as well as some scribe marks  --the guy who made this micro mouse is a machinist or a sheet-metal guy.

Paul is very correct. The aluminum angle iron is attached to the PCB with pop-rivits. The wheels are held with a regular stovebolts and nylon lock nuts. I am sorry, but looking at the picture the mounting seems very clear to me --could you restate your question and tell us specifically what you are confused by?

He's using rivets, but why can't you use 2 small bolts and nuts on each side to attach mount plate to circuit board? It looks like the wheel spins freely over the axle which is another bolt with a nylon lock nut. That's what it looks like the picture shows.