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Eco19R:
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 .

Hal9000:
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.

Hal9000:
Also, this has some neat little nuggets of information about locomotion or whatever. Skidding included.

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

Admin:

--- 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?
--- End quote ---

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?
--- End quote ---

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?
--- End quote ---

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 . . .

sdk32285:
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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