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Offline Eco19RTopic starter

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3 questions -
« on: May 26, 2007, 12:42:04 PM »
Hello, I have been wondering about these questions for a while and I think one of you may be able to help me - I will try to articulate my questions the best I can but I am not sure if I am describing them accurately.

1. - Is it possible to make a functional robot base with only 2 wheels - instead of the standard 2 + caster? It obviously could not climb up any slopes but for flat areas would it be possible?

2. - Whats the best way to mount wheels to bearings then bearing to the base? I have been running into this issue and I am not sure how to solve it. I am also looking to make a tracked bot but I don't want to have to machine all the "track roller things" my self, Does anyone have a good idea on mounting these plastic "track roller things" ( http://www.hobbyengineering.com/H2028.html) to bearings then bearings to the base?

3. Are there any guide lines for designing a 4WD robot that uses skid steering? I am worried about the friction on certain surfaces being so great that it wouldn't be able to turn - do these worries have any merit?   

Thanks for any input you can provide .
« Last Edit: May 26, 2007, 12:42:46 PM by Eco19R »

Offline Hal9000

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Re: 3 questions -
« Reply #1 on: May 26, 2007, 02:32:49 PM »
For 2 wheeled robots, you could use a barrel design, wheras the pure 'belly' weight of the canister would stop the body rotating around instead of the wheel. I'm sure the word torque comes in there somewhere. I'm sure I have done this before with some lego.

Then there is also the segway robot. I remember seeing someone built a particularly nice lego mindstorms one once. Lots of PID control I would imagine.
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Offline Hal9000

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Re: 3 questions -
« Reply #2 on: May 26, 2007, 02:35:50 PM »
Also, this has some neat little nuggets of information about locomotion or whatever. Skidding included.

http://micromouse.cannock.ac.uk/dynamics/corners.htm
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Offline Admin

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Re: 3 questions -
« Reply #3 on: May 26, 2007, 06:45:53 PM »
Quote
1. - Is it possible to make a functional robot base with only 2 wheels - instead of the standard 2 + caster? It obviously could not climb up any slopes but for flat areas would it be possible?

A segway balancing robot? Using a castor is much easier, tho . . .
Search this forum for 'balancing' to get more info on it.

Quote
2. - Whats the best way to mount wheels to bearings then bearing to the base? I have been running into this issue and I am not sure how to solve it. I am also looking to make a tracked bot but I don't want to have to machine all the "track roller things" my self, Does anyone have a good idea on mounting these plastic "track roller things" ( http://www.hobbyengineering.com/H2028.html) to bearings then bearings to the base?

Treads arent as good as people think. Avoid them if possible.
http://www.societyofrobots.com/robotforum/index.php?topic=760.0
http://www.societyofrobots.com/robotforum/index.php?topic=850.0

Quote
3. Are there any guide lines for designing a 4WD robot that uses skid steering? I am worried about the friction on certain surfaces being so great that it wouldn't be able to turn - do these worries have any merit?

Estimating the friction force, and knowing the torque from the motors, you can actually calculate this. This tutorial should give you enough information to calculate it:
http://www.societyofrobots.com/mechanics_statics.shtml
You will need to use the friction equations, torque equation, and moment arm equation.
(it may take a bit of thinking before it makes sense to you)

hope that helps . . .

Offline sdk32285

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Re: 3 questions -
« Reply #4 on: May 26, 2007, 08:04:49 PM »
Also for skid steering you need to take into account the forces on the side of the tire/track and on the bearing/arm that supports the wheel while turning.
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Offline ed1380

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Re: 3 questions -
« Reply #5 on: May 26, 2007, 09:11:43 PM »
2. - Whats the best way to mount wheels to bearings then bearing to the base? I have been running into this issue and I am not sure how to solve it. I am also looking to make a tracked bot but I don't want to have to machine all the "track roller things" my self, Does anyone have a good idea on mounting these plastic "track roller things" ( http://www.hobbyengineering.com/H2028.html) to bearings then bearings to the base?

my guess would be pillow block bearings, but that depends on size
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Offline Eco19RTopic starter

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Re: 3 questions -
« Reply #6 on: May 26, 2007, 09:24:27 PM »
2. - Whats the best way to mount wheels to bearings then bearing to the base? I have been running into this issue and I am not sure how to solve it. I am also looking to make a tracked bot but I don't want to have to machine all the "track roller things" my self, Does anyone have a good idea on mounting these plastic "track roller things" ( http://www.hobbyengineering.com/H2028.html) to bearings then bearings to the base?

my guess would be pillow block bearings, but that depends on size


I actually thought about that but the cost of the pillow block set would be greater then the robot itself.

I could machine my own but I don't have CNC set up on my mill and it would be a pain to do it by hand.

Off Topic: anyone know of a good 4 axis stepper motor driver for under 100$USD?

Offline Ro-Bot-X

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Re: 3 questions -
« Reply #7 on: May 26, 2007, 11:11:25 PM »
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Offline sdk32285

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Re: 3 questions -
« Reply #8 on: May 26, 2007, 11:56:39 PM »
Instead of using all the track rollers, just use one on each end and place a smooth piece of plastic along the surface that the track is running.
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Offline Eco19RTopic starter

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Re: 3 questions -
« Reply #9 on: May 27, 2007, 01:07:27 AM »
Instead of using all the track rollers, just use one on each end and place a smooth piece of plastic along the surface that the track is running.

Thats actually a great idea I could even machine the grooves for it so it wouldn't get out of place - it still leaves the problem of mounting the two end rollers to bearings though, I don't have any aluminum ATM - I only have a bunch of cutting boards, Anyone have an idea on how to machine and setup a pillow block configuration for each side on one end? I got a couple of rough ideas but nothing to point of actually being able to create it.

Thanks everyone for all the help and ideas -

Offline Ro-Bot-X

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Re: 3 questions -
« Reply #10 on: May 27, 2007, 03:53:26 AM »
Well, if you have a milling machine it is fairly easy to manufacture a pillow block. You just take a square block of aluminum a little bigger than the ball bearing you want to house. Drill a hole in the center on the face of the block, a little bigger than the shaft going through the ball bearing. Then, install a flying cutting tool on the milling machine and cut out the hole to the exact diameter of the bearing but don't go all the way out. Leave a small shoulder so the bearing doesn't get out. If the dimensions are small, you can drill it. Press fit the bearing inside. If the hole is large, then cut one of the sides with a hack saw. Then on the bottom of the block drill on each side a long hole, going all the way out to the top. Mount the block on the chassis using 2 long bolts with nuts on top. When you tighten the nut on the side that has the cut it will also tighten the bearing inside the block.
All done.
« Last Edit: May 27, 2007, 04:00:00 AM by Ro-Bot-X »
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Offline Ro-Bot-X

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Re: 3 questions -
« Reply #11 on: May 27, 2007, 04:17:37 AM »
Take a look at this site. They have motor mounts, but the mounts may be used for bearings also. At the bottom of the page you will see exactly the type I was describing above, only instead of a cut on one side, it is cut in half.

http://www.robotmarketplace.com/marketplace_mounts.html
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Offline Eco19RTopic starter

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Re: 3 questions -
« Reply #12 on: May 27, 2007, 11:30:02 AM »
I think I can do that - Ideally it seems you should have two sets of ball bearings for each side, anyone know a cheap place to buy fairly small bearings?  I went to a place where I live that sells motion products but there stuff was pretty expensive.

Another idea would be to machine the wheels themselves so the bearing fit inside them and have the axle attach to the base,

Anyway thanks again for all the help

Offline Ro-Bot-X

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Re: 3 questions -
« Reply #13 on: May 28, 2007, 01:58:05 AM »
Another idea would be to machine the wheels themselves so the bearing fit inside them and have the axle attach to the base,

You will need a lathe to machine the wheels. On a second thought, you can do a brazing to attach a toothed belt pulley to the wheel. You can also encapsulate the bearing inside, something like this:

         rubber O ring on the wheel
       /
 _ O _     brazing
|   V   | /         tooth belt pulley
|        |/____ /
|   ___||__    |
|  |i--------i|  |
|_|| _/ \_ ||_|
          o ----------------ball bearing
-- . -- . -- . -- . --

I draw only the upper half of the section through the wheel/bearing/pulley assembly. I hope it is clear enough. You can machine the wheel on the mill and also enlarge the hole of the toothed belt pulley.













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Offline Eco19RTopic starter

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Re: 3 questions -
« Reply #14 on: May 29, 2007, 12:53:45 AM »
Thank you for the information -

I can more clearly see what I think I am going to do (lol)

but I still have another question about machining ( see ASCII art) -


What would I use as a "washer" to stop the rod for sliding back and forth
Also what would you suggest for a "endcap" to stop the whole rod from sliding off?

I thought about drilling into the center of a larger solid rod then drill another hole which you would tap and put a setscrew in - do you have any easier suggestions?
   
||
||    |||     ||    |||  < Pillow Block
||==|||==||==|||= < End of Rod
||    |||     ||    |||
||     ^      ^
^          Sprocket
       
     pillow Block

wheel

= < Space



I still need to find a legitimate place I can purchase ball bearings from - also sprocket and chain sets.

A question thats a bit off topic - What blade do I use on a miter saw to cut aluminum?

I used an abrasive blade made for metal but it didn't work well. 

Offline Ro-Bot-X

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Re: 3 questions -
« Reply #15 on: May 29, 2007, 01:57:34 AM »
To stop the axle to slide sideways you can have the ends threaded and use nuts to tighten the ball bearing on one end and the wheel on the other end. In between you can use spacers (several washers). By the way, don't forget to have a split unlocking washer at the ends. Or, you can have the whole axle threaded and use nuts as spacers.

To cut aluminum I have allways used a metal cutting blade on my grinder. I have to clean the cuts, but I don't like to cut small pieces with the miter. If they are realy small, I use the Dremel with a metal cutting blade.
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Offline Eco19RTopic starter

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Re: 3 questions -
« Reply #16 on: May 29, 2007, 11:59:51 PM »
Thanks, again for the help -

I tried cutting some aluminum with my miter saw with a different blade - it didn't go so well, I was using a carbide blade - well the aluminum broke off the clamp and flue out in two pieces and the bolt that held the blade came lose - I am lucky I did not get hurt, I guess I will have to stick to using my band saw - I never seem to be able to cut straight using it.

Is double sided sticky tape worth using to hold certain parts together?, I have been wondering this and its a bit embarrassing to use it but it seems to fashin mounts for certain things would take too much time.

This is a bit off topic but -

Should I cover my electronics test equipment when I am working with metals? Its on the other side of the room and obviously off but I was wondering if it would still be needed
« Last Edit: May 30, 2007, 01:52:00 AM by Eco19R »

Offline dunk

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Re: 3 questions -
« Reply #17 on: May 30, 2007, 05:32:21 AM »
i really don't get why people always want to use power tools.
for making small, straight, accurate cuts in aluminium an old fashioned hand hacksaw is the best tool for the job.

dunk.

Offline Admin

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Re: 3 questions -
« Reply #18 on: May 30, 2007, 06:58:28 AM »
Quote
Is double sided sticky tape worth using to hold certain parts together?, I have been wondering this and its a bit embarrassing to use it but it seems to fashin mounts for certain things would take too much time.
For really small robots, double sided sticky tape is a blessing. Use it profusely, such as for mounting servos. For medium size robots I'd avoid it except for special occasions. My only complaint about the tape is sometimes its really really hard to remove . . .

Quote
i really don't get why people always want to use power tools.
for making small, straight, accurate cuts in aluminium an old fashioned hand hacksaw is the best tool for the job.
gasp!!!!!!!!
thats like programming in binary!!!!!!!!! :P

Offline Eco19RTopic starter

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Re: 3 questions -
« Reply #19 on: May 30, 2007, 10:48:41 AM »
i really don't get why people always want to use power tools.
for making small, straight, accurate cuts in aluminium an old fashioned hand hacksaw is the best tool for the job.

dunk.

If you are making 20 cuts its not practical to do it by hand.

one other thing -

I know I have asked this question before and I am sorry to be pestering everyone with it -

Where can I purchase cheap ball bearings - small gears and chain and sprocket sets (live in USA)?

I got my design but I have ran into a problem of not being able to acquire the needed materials.


« Last Edit: May 30, 2007, 10:54:36 AM by Eco19R »

Offline Ro-Bot-X

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Re: 3 questions -
« Reply #20 on: May 30, 2007, 01:05:40 PM »
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Re: 3 questions -
« Reply #21 on: May 30, 2007, 01:12:01 PM »
dont forget mcmaster.com!

 


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