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So it would be easier to balance a machine with the rider standing over the wheel axles than under the axles? Hmmm... A pendulum platform stabilizes at least some of the weight it is supporting, of course the overall CG is very much above the axles. It does this naturally and should require less power from the motors to keep a rider upright. In an inverted pendulum base all weight is in an inverted pendulum status and all of it requires stabilization. The following example shows two yard sticks one supported at its end the other also supported at its end (superglued) but it is nested in a balsa pendulum. Any difference between the two? |
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My brother explained to me like this:
With the platform above the wheels, the motors are always playing catchup when trying to balance. With the platform below the wheels it allows the motors do what they need and have the platform follow instead of the other way around. I hope that helps, it definitely cleared it up for me. |
hmmm...
well, it wouldn't be hard to adjust the deck height to change CG on the design we are going to build, so we'll probably try both. But the Segway looks as if the deck is above the wheels, so that is our goal :-) |
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With the platform below the wheels....when you start moving, the front of your'e platform will dip down upon acceleration...correct? If you correct this initial lean by compensating in the opposite direction wouldn't, a pendlious action occur...rocking back and forth as the rider tries to maintain ther own balance? This act of acceleration would cause you to lean even further foward before you had a chance to compensate...and if you had true segway like function...go even faster?
If you had your'e platform on top of the wheels, I think it would be harder on the gyro, but easier to maintain balance upon acceleration. |
The deck dips down in front in advance of going forward not because of it. A gyro or manual Segway has to tilt accordingly to the amount of acceleration required. This would happen by the way even if your Segway has it's platform over the axles.
Yes, the Segway has its platform well under the axle line and although it is harder to make them like this it is for good reason. The heaviest things on it are at the lowest possible position...that is the batteries, then the motors and the aluminum casing etc. If they were trying for a high CG they would have put the batteries in the steering stalk like the batteries in a flashlight. I finally made a dv .mpg clip of the KnightKrawler at it's VCU debut. (I apologise for the poor quality animated gifs) I wish it were lighter but you can adjust that I hope. I'll make a link to it soon. The pendulous action yuo describe certainly can happen on our machine as a result of over correcting and in the case of the Segway as a result of a new rider not trusting the stablility of the machine. I will say that in both cases it is experience and anticipation that will fix that problem for the most part. Looking at the Video from March 2003 of me on that knightKrawler I can say I am smoother than that now! And a Segway with the base over the axles will probably be fine provided there is power to make it work for a more novice rider. |
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yep, i was wrong.. for some reason i thought the deck was higher...
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Here is the only DV Mpeg of our KnightKrawler debut at the 2003 VCU event, the video software doesn't have a working provision for lightening the picture....it came with the capture card.
If anyone has a video of our KnightKrawler it might be worth a Team 122 Omniwheel Pendant! If you have the video of Dean Kamen riding our KnightKrawler at VCU, it is worth THREE pendants!!! Check out the video....KnightKrawler Debut at VCU http:/wihs.zapto.org/~knightkrawler/ |
that is a nice clip... and out of curiosity, what are these pendants that you speak of? They sound like a prestigious prize :-)
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Thanks! And yes the Omni Badges are cool...any color bead you want too! The omni rollers actually spin also!
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I put up a little insight to what i'm thinking about the center of gravity on the website. Pardon the connection problems you may have the server isn't 24/7 (it's my personal pc).
I'm trying to post as fast as possible, but i've spent the last 4 days running between prom and graduation parties. It's been nuts! Will |
WOW, that pendant is pretty nice...
Makes me wish I had the video clip your looking for :-) ok, Willum back to CG |
471's Team segways
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Here are team 471's segways, two different prototypes, one is controlled with a central joystick and the other uses two drill housings for speed control. They move around pretty quick
with those FP motors, and you can hear them comming because the motor gears make some noise. They have casters on the back now, but I think they were originally trying a tilt switch balance system where the motors would be compensating for the tilt of the base due to a smooth teflon slipper switch mounted under the platform that would ride on the floor. |
Oh hey this thread is still here good. I had an idea for my solution to the sloppy drill problem. I'm gonna try this whether or not you guys like it ;) but I'd like an opinion. Also, much thanks to Andy Baker for this idea (in other words, if it blows up and hurts someone blame him! :D ) Anyway, since the drills have the power I need to move this thing and the FP are tight enough for the balance I was thinking about joining them. Basically both motors with a sprocket on an output shaft leading to a loose shaft for lack of better words. Chains link them and I think I can play around with the ratios to get the RPM close enough. If it works then I will have a sprocket take the output and chain it to the wheels. The idea is basically the FP will keep you steady with the Bosch throwing in horsepower so you wont be crawling. Any comments? and keep in mind even if this is a doomed failure I'm still trying, I'm stubbornly optimistic plus I need an excuse to get myself to learn ratios and the like.
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You would definitely have a quite powerful machine. However, chaining the output to the wheels would give you a lot of unwanted play (or little play and excessive chain tension). The best way I've found so far is to just make a custom drivetrain for the Chias. Or just settle for less power an use the window motors (but not the new ones, they get to have 45 degrees of play after a bit of use).
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Not a bad idea...and you could mount a dual chain tensioner.
This is why these forums work so well...ideas can just flow out and help everyone who participates. Get going Matt, build it, it'll be fun and you won't regret it. And you ask for comments...one I could give is that when you settle on a matching gear ratio between the two motors, consider that the top speed matchup is not that important unless you are making a four wheeled "segway" because you seldom will reach top speed. This is because you need to hold some speed in reserve to make tilt corrections as you ride. Can't fix the slop in the drill motor? I take it that the drill motor you are using is the new one then? Is the clutch different in it? |
I'm begining to think that i'm the only graduated high school senior crazy enough to try and build a mostly functional self balancing robotic scooter.
Is there any knowledge of any other teams trying to do this, or is everyone just building segway look-alike's??? |
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The J-Way as seen (and built only the night before) at Nationals. Sorry, it's the best picture I have. J-Way v.2.0 is expected to have balancing and speed controlling capabilities :p
Now, WHEN J-Way v.2.0 actually is developed, well that's another story...not very easy to find time when FIRST is a full-year program. :cool: |
Was The "J-Way" a 190 WPI project or Team 871's?
It went everywhere at the Nationals I remember! |
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And thanks for the encouragement guys, these forums rock! |
The "J-way" is a team 190 project....
Team 871 has no affilation with Team 190.... ppppppttttt on the J-way :-P (WernerNYK is a former Team 871 student team leader) WPI yada yada yada :-) |
Meet the ev warrior!!
http://www.enigmaindustries.com/Bosch_EV_Warrior.htm These powerhouses are designed to move a human on a bycycle. An alternative to the motors that you see in the kit. It may not be as powerful at 12volts but you can definately overvolt these to 24 volts. You really can not do that with the drill motors. Quote:
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Here's a technical paper on a "mobile inverted pendulum" that could be of some use.
JOE And some videos of it in action. http://leiwww.epfl.ch/joe/ |
low-tech solution
I remember seeing a two-wheeled balancing robot made with Mindstorms that used IR proximity sensors to balance instead of a gyro. We used some of the Sharp IR sensors this year, I don't have the part number handy but they're the ones with 6" - 6' range. Using one on the front and back, pointed at the floor, you can figure out your angle of tilt. They're pretty fast, you might be able to make a balancing platform without a computer, just a closed-loop with the sensors as feedback.
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I've considered a single point balancing device. You couldn't use only one wheel, you'd need a sphere to balance on. You'd need to come up with a fancy turning mechanism or program because leaning like on the segway will only provide motion in that direction, not spin the rider around.
otherwise it's a good idea. just a little out of the range of the parts we're supplied with. Will |
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Re: low-tech solution
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My concern is that the IR sensors would be prone to errors depending on what type of surface you are running on. I would guess and ultrasonic signal would be better, like what they use in wall "stud finders". I like the gyro idea the best though, The Craigway's goal is to mimic the Segway, with the standard KOP. This way other teams can duplicate the results (after we are finished that is :-) |
I have used SHARP GP2D12 IR proximity sensors and surprisingly, they are almost entirely impervious to to differences in color, texture and angle. Their man drawback is that they are not linear and this must be corrected for. The problem is especially bad at large distances. Other than that, though these things are great. Sonar could be another interesting option.
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Ok i finally revealed some stuff for the holiday weekend. This includes some of the physics and two key lines of code.
Enjoy! (it's on the incomplete, but available MASSIVE PHYSICS page) Will :D http://frohawk.no-ip.org/physics.htm |
Ahh a fellow case modder as well!
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Alright, working on the design guys. Does anybody know of a drill motor model for Inventor besides the FIRST one? The FIRST one has a tendency to bring my system to its knees in crashes. Anyhow, using a 3:1 reduction on the drill to sync it with FP at 100 rpm, expecting about 65 rpm under normal load. I'm looking in to using 14" bicycle tires and wheels. Anybody have an opinion on how well the FP can handle the tweaks back and forth to balance? Can it at all? The drills wont kick in until you start moving, that darn slop.....Thanks
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we used the FPs on the Craigway, they respond well, just not powerful enough for dynamic balancing. And I would take the stop pins out of the drill motors, otherwise you are going to wind up throwing someone off the device when it comes to a screeching stop.
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Stop pins and....
That is a good point MrB, you have to be able to coast and use "engine braking", and that reminded that the picture I put in of the 2001 Drill motor and it's source of slop does not mention that we build our own shafts and the original shaft and it's related parts ALSO may contribute to play...I think it is the "Hammer" feature.
By the way I got a big kick out of the Joe series of balancing robot videos...high tech and what a riot! And it would do no harm to take a 30 LB weight and add it to the stalk to see what happens! |
I think we talked about this before school let out B.
You need to keep feeding motor power out and not let the scooter freewheel. Gaining undesired momentum will add forces that are unexpected to the code. Say for instance going up or down a hill. The program, based upon angle of tilt, must tell you how fast to go. DON'T USE FREEWHEEL!!! btw, the FP's seemed powerful enough to dynamically balance, but just weren't programmed to come back hard enough under a limited tilt. I'm working out the bugs, but without the prototype to play with all i got is theory and roboemu code. Will |
Ok, quick question, with 150lbs total load and 100rpm free speed with drill and FP together, what do you think it will run at under load? I'm hoping between 60 to 65rpm but I'm no expert...thanks.
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Ok see here's where we start diving into unknown territory.
You never will have 150lbs of load with a 150lb rider. Following what I did. 666.4 newtons is the full force of the rider, multiply that by the cosine of the angle of tilt. your answer to that is your horizontal angle of force. Try it, follow what i did, just change the angle and you'll see how the force increases as the angle decreases. Figuring out how torque, rpm, and theoretical force all come together... that's where i'm having a problem. |
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Uhhh.. I can add....? OK, wanna give us that in laymans? please? |
hmmm... in physics there's a thing called normal force. That is, the force that pushes back at you. When you stand on the ground, your body pushes into the ground, but the ground pushes back up.
When riding the Segway or the Craigway the normal force is much different. Your body pushes straight down, always, but the normal force pushes back up from the axle at the angle you are tilted. What I tried to say is that when you break up that angular force into it's two direction, horizontal and vertical, the horizontal force is never a full 150 pounds. If you tilt 10 degrees forward your horizontal force is about 26lbs. I'm getting lost on how i get that force out of the motors... I've calculated out momentum, rpm, torque yadda yadda yadda... So i guess those engineers get big $$$ for a reason. I hope that helped a little. |
You probably know this already but I just didn't want anyone to forget the fact that the normal force is always perpendicular to the supporting surface.
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