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 [DPRG] Walking robot Message index sorted by: [ date ] [ thread ] [ subject ] [ author ] Previous message: [DPRG] Contest Scores Next message: [DPRG] Walking robot Subject: [DPRG] Walking robot From: David P. Anderson dpa at io.isem.smu.edu Date: Wed Sep 24 13:34:01 CDT 2003 ```Howdy Chuck wrote: > > >People don't "fall up" stairs. > >I'm not sure that is true. Can you elucidate? > > A stair climbing gait depends on a balanced vertical ascent. It becomes > more of a crawl the farther forward you lean up until you get to the > classic "kid running up stairs" gait using the hands/arms for stablizing > the torso. I'm trying to square that with what I've learned about dynamic balance from the two-wheel balancing robot. The two-wheel balancing robot and the two-legged balancing human seem to me to be doing basically the same thing, as far as the physics is concerned. Both maintain balance by keeping the base underneath the center of gravity. Both move forward by allowing the center of gravity to fall forward, and using that falling force to counter-balance the torque required for acceleration and locomotion. That is, the forward falling weight of the upper part of the body is required to keep the torque required for forward movement from flipping the body/robot over backwards. In this way the human and the robot are both always falling forward when in forward motion. Here is a video of the robot balancing while standing still (well, I'm pushing it around) http://www.geology.smu.edu/~dpa-www/robo/nbot/nbot2/nbot2_push.mpg and here is one of it driving, and leaning forward to accelerate and maintain constant velocity: http://www.geology.smu.edu/~dpa-www/robo/nbot/nbot2/nbot2_circle_lowres2.mpg where you can see that it must lean forward slightly in order to overcome the friction of the carpet, even when it is not accelerating. Now if the robot were to drive from a smooth low friction surface like hardwood to a higher friction surface like heavy pile carpet, more torque will be required to maintain the same velocity, and the robot will have to lean further forward in order for the "falling" force to counteract the increased torque. In the same way, if the robot (or human) drives from a smooth level surface onto an inclined ramp, more torque is required to go up the ramp, and the robot must lean over further to counter-act (provide for) the increased torque. Here is a video of the robot going up and down a ramp: http://www.geology.smu.edu/~dpa-www/robo/nbot/nbot2/nbot3_ramp2.mpg Well, it got going too fast and fell down on the first try, but thereafter you can see that it has to lean further forward to handle the increased torque required to lift it's body weight when it goes up the ramp. Now, it seems that you can make that ramp as steep as you want, as long as the robot has sufficient batteries/motor/torque to climb the slope, it will just lean further and further forward, and it is still, and must be, falling forward, falling "up the slope," in order to go forward. At some point the amount of forward tilt required will run into the increasing steepness of the slope, the robot will assume the classic "kid running up the stairs" posture. Stairs are just an inclined slope that is customized for feet instead of wheels, so your foot has a nice flat place to support it, but the human like the robot must have a falling center of gravity in order to counteract the torque required to ascend. So the human walking gait (or two-legged robot walking gait), in my understanding, does and in fact must, fall up the stairs. Stairs are just a special case of an inclined plane, and an inclined plane is just a special case of a level plane, and the same walking and balancing principles would appear to apply to all three, both for dynamically balancing two-wheel robots and for dynamically balancing two-legged humans. Yes? As an aside to the wheels vs. legs discussion, I'd be interested to see how one of the two-legged industrial walking robots, dynamic or static or any combination, might handle something like this: http://www.geology.smu.edu/~dpa-www/robo/nbot/hill_loop_cpk.mpg dpa ``` Previous message: [DPRG] Contest Scores Next message: [DPRG] Walking robot Message index sorted by: [ date ] [ thread ] [ subject ] [ author ] More information about the DPRG mailing list