So there is a misconception that needs to be addressed:
Simple physics shows that the higher up the center of gravity, the easier it is to balance. The batteries are up high so that the bot can balance at all, otherwise it would just fall over all the time (the distance actually changes how fast a response time is needed to keep the bot balancing) Try balancing a long broom and then a pencil. If you can balance the pencil you're a super hero...or something.
@ryan: Wow that was a concise explanation of why he was wrong. Oh wait. It wasn't. I'm not a physicist, but I tend to agree with his point. If you want to sway my opinion, you're going to have to work a little harder than that.
He is definitely right. It's called moment of inertia. An object with a higher moment of inertia will respond more slowly to a given moment than one with a smaller moment of inertia. So, if you had lighter batteries or moved them closer, the moment of inertia would be less and it would tip over faster, probably too fast to balance.
@ryan: Have you ever taken a physics course? If so, you must have failed cause arthur is 100% right, I actually came to comment the exact same thing he did.
Precisely. What the builder needs to do is to leave it with heavy batteries, but raise them a little higher.
@ ryan
An even better way to explain this (so you don't try and give us 'but a broom and a pencil are two different things' nonsense) is to take a broom and balance it on your hand with the head facing upwards. Easy, no? It's top heavy, just like this robot.
Now try turning the broom around so that the head is on your hand and the stick is facing upwards. Point proven.
Okay so here's the explanation, a higher moment of inertia decreases the necessary response time, but "Simple physics shows that the higher up the center of gravity, the easier it is to balance" is the exact opposite of the truth. Why do you think tight rope walkers carry those large sticks? It's because they lower their center of gravity. Or think about those little balancing birds (like this http://bobscrafts.com/bobstuff/balance.htm) where you can balance it on its beak without any effort whatsoever. This is because it has a low center of gravity (the wings lower it significantly). If it had a higher center of gravity, do you think it would be easier to balance?
The only problem with giving it a higher centre of gravity is that you then end up with a smaller angle at which it can be out before the motors cant move fast enough to get it upright. So bassically it stands upright more easily. But once it tilts, you have to get it back upright quicker. But yes its easier to do it this way.
um, the simplest way i can explain this is to use torque, a pretty simple concept if you have a definitive pivot point. Torque = (distance from pivot point) x (force applied) if there is more mass towards the top of the object, it will require more force to torque the object and make it fall over since everyone knows F=ma. if there is less mass towards the top, it will require less force to torque the object and therefore will make it easier for an object to fall over.
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So there is a misconception that needs to be addressed:
Simple physics shows that the higher up the center of gravity, the easier it is to balance. The batteries are up high so that the bot can balance at all, otherwise it would just fall over all the time (the distance actually changes how fast a response time is needed to keep the bot balancing) Try balancing a long broom and then a pencil. If you can balance the pencil you're a super hero...or something.
In short: Batteries high = Good.
-A
Do us all a favor:
http://en.wikipedia.org/wiki/Physics
I've always said that bobo dolls are products of black magic.
@ryan: Wow that was a concise explanation of why he was wrong. Oh wait. It wasn't. I'm not a physicist, but I tend to agree with his point. If you want to sway my opinion, you're going to have to work a little harder than that.
@ryan
He is definitely right. It's called moment of inertia. An object with a higher moment of inertia will respond more slowly to a given moment than one with a smaller moment of inertia. So, if you had lighter batteries or moved them closer, the moment of inertia would be less and it would tip over faster, probably too fast to balance.
@ryan: Have you ever taken a physics course? If so, you must have failed cause arthur is 100% right, I actually came to comment the exact same thing he did.
"Try balancing a long broom and then a pencil."
@ Arthur
Precisely. What the builder needs to do is to leave it with heavy batteries, but raise them a little higher.
@ ryan
An even better way to explain this (so you don't try and give us 'but a broom and a pencil are two different things' nonsense) is to take a broom and balance it on your hand with the head facing upwards. Easy, no? It's top heavy, just like this robot.
Now try turning the broom around so that the head is on your hand and the stick is facing upwards. Point proven.
I seriously grabbed a pencil and a broom. Physics experiment at a moment's notice!
Okay so here's the explanation, a higher moment of inertia decreases the necessary response time, but "Simple physics shows that the higher up the center of gravity, the easier it is to balance" is the exact opposite of the truth. Why do you think tight rope walkers carry those large sticks? It's because they lower their center of gravity. Or think about those little balancing birds (like this http://bobscrafts.com/bobstuff/balance.htm) where you can balance it on its beak without any effort whatsoever. This is because it has a low center of gravity (the wings lower it significantly). If it had a higher center of gravity, do you think it would be easier to balance?
The only problem with giving it a higher centre of gravity is that you then end up with a smaller angle at which it can be out before the motors cant move fast enough to get it upright. So bassically it stands upright more easily. But once it tilts, you have to get it back upright quicker. But yes its easier to do it this way.
um, the simplest way i can explain this is to use torque, a pretty simple concept if you have a definitive pivot point.
Torque = (distance from pivot point) x (force applied)
if there is more mass towards the top of the object, it will require more force to torque the object and make it fall over since everyone knows F=ma. if there is less mass towards the top, it will require less force to torque the object and therefore will make it easier for an object to fall over.