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profegross

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Reply with quote  #1 
Brand new team here, at a school that has never had a robot, nor a robotics club, nor do my poor kids have a sponsor that knows anything either.  Can anyone point me to anything that will give us a few ideas on how to attach wheels we've created to the motors?
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jgraber

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Reply with quote  #2 
The usual method I suggest to our rookie teams, and provide them with tools to build is this:
  1. use 1/2" plywood circles of 6 to 12" diameter as wheels,
  2. use Large motors for wheels
  3. use a 2x2x1/2" block of aluminum (30k psi) as a wheel hub to hold the axle, estimated force 17k psi.
  4. use the #10-32 x 1" alloy (70k psi) socket headed cap screw as a set screw
  5. You can drill and tap a set screw hole from the edge of the block to the axle hole
  6. Or, drill a 3/8" to 1/2" hole midway between the axle hole and the flat edge, and insert #10-32 nut crossways, "crossnut", which saves you from having to use a tap.
  7. drill some other holes in the corners of the block to use to bolt the wheel onto the block;  You can use 3/8" countersink and press fit #8 nuts on the back side, and use #8x1" (team purchased screws shorter than ckit same type are allowed this year) #8-32 machine screws to bolt the wheel to the plywood.
  8. Its easier to drill several on the long Aluminum bar at one time, and cut them up afterward, as long as you remember to leave room for the saw kerf.
  9. I start by using a 1/4" drill for all the holes, then use the right hand drill bit in this picture to increase the size, and chamfer all the edges.   http://www.harborfreight.com/3-piece-titanium-nitride-coated-high-speed-steel-step-drills-91616.html
  10. Here is a picture of semi-finished wheel hub.
  11. WheelHub.jpg 

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profegross

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Reply with quote  #3 
I had to read this about 10 times, but I get it, and this will work very well I think for our purposes.  Our Ag teacher is willing to help teach the kids how to do what's necessary, so I think we can make it work!  Thank you so much!
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jgraber

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Reply with quote  #4 
I would be pleased if you would post a description that you would fine easier to understand, or takes less number of times to read.
  Harbor Freight currently has a sale on the 3-bit step drill package for $9 instead of $13.
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profegross

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Reply with quote  #5 
Lol, I think I didn't make myself clear. Your explanation was absolutely brilliant and perfect. I only meant that because I am so out of my depth it took me a while to figure it out, but I was excited to be able to do so to finally help my kids a little bit! I can't thank you enough. I wasn't in any way trying to imply you weren't clear or helpful. You absolutely were amazing!

Quote:
Originally Posted by jgraber
I would be pleased if you would post a description that you would fine easier to understand, or takes less number of times to read.
  Harbor Freight currently has a sale on the 3-bit step drill package for $9 instead of $13.
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shcbest

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Reply with quote  #6 
What do you use to cut the aluminum bars?
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profegross

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Reply with quote  #7 
My student says he used the cold saw from our Ag barn, but any saw with a blade designed to cut metal would do.
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ralsobrook

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Reply with quote  #8 
When using power tools, generally speaking, I was always taught in the machining world that any blade designed to cut wood would also work well for cutting 6061 aluminum at the same (or a little slower) cutting speed. I would be hesitant to use a jigsaw ( due to the tendency of the blade to bind in the material ), but a reciprocating saw, skill saw, table saw, band saw, miter saw, or a good old fashioned hack saw should do the trick. If you plan to use any saw with a circular blade, you might want to lightly coat either the blade or the material in wax to prevent pieces of the aluminum from getting stuck in the gullets ( spaces between the saw teeth ).
I hope I have been helpful, but don't just take my word for these methods. As always, if you are trying to do something that you think is potentially unsafe, or you are uncomfortable with, just find another way. 
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jgraber

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Reply with quote  #9 
I've had bad luck with a general purpose carbide tipped chop-saw blade in a chop saw.
I've had reliable results with a Alumicut chop-saw blade:  triple-chip ground, zero rake angle;  but the chop saw generates a cloud of glitter.
This year, the build shop had a horizontal metal cutting band saw.  Compared the the chop saw, it was narrowerer kerf, quieter, cleaner, equally fast, but somewhat less precise.  It leaves a puddle of oily aluminum sludge, rather than a air-borne cloud of glitter.
Last year, we had a hack saw competition. two different teams were able to cut through the block in < 6 minutes with a 12-18t hacksaw.
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jgraber

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Reply with quote  #10 
Dallas BEST just had demo day on 10/29/2016, and I saw some different types of hubs.
- some like mine above
- some with threaded holes, some with phillips head plain steel screws
- some in the two piece style clamped together by a 1/4" threaded rod+2 nuts, on each side of the hole.
- One rookie team used a slice off the end of a 2x4 with a wood screw as a set-screw;  through some miscommunication, they missed kickoff afternoon build session.  
- One rookie team used  block of plywood with a cross nut and machine screw.   It is the best looking wooden hub I've seen.  It if works well on game day, it would be a good addition to my list of ideas for "Least Expensive robot".
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