 | | Re: Newbie needs Help
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(...) Steve, Philo's page on 'Wheels, Tyres & Traction' seems to imply that increased speed will not make much of a difference or am I reading that wrong? By 'mechanically connect' do you mean by using two differentials? The maximum 'safe' gearing (...) (18 years ago, 6-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help
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(...) One rotation sensor and a differential will allow you to compare the rotation of two wheels. If the driven wheel and the undriven wheel come in the two sides of the differential, and the rotation sensor is connected to the drive ring, then the (...) (18 years ago, 6-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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Some varied thoughts here: (...) I might be wrong, but my understanding of the Lego differential gearing is that if both shafts are turning at the same rate and direction, the outer gear/shell will turn at the same rate as the axles. Only when the (...) (18 years ago, 6-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help
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(...) What I'm saying is that if the robot is moving along at (say) 3 inches per second - then the drive wheels will get most traction if they are turning at a speed equivelent to 3 inches per second. If they are rotating faster than that (because (...) (18 years ago, 6-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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(...) I think you need another pair of gears on one of the wheels to reverse its direction. If you are going to use a rotation sensor to measure the slippage then you need to realise that the sensor is notoriously poor at very low speeds. You'll at (...) (18 years ago, 6-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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(...) Quite true. My bad. -dave (18 years ago, 6-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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(...) Actually it does - barely. With the increased current, RCX output voltage drops, so does motor stall current. See these compared charts: (2 URLs) Philo (18 years ago, 7-Jun-06, to lugnet.robotics, FTX)
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| | Re: Newbie needs Help (diff sensor)
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Philo, That's interesting, and looks to explain why it is that I've never been able to observe the RCX output going to thermal or current protection cutoff? I've one largish sumo type bulldozer style robot with 4 treads that can easily push 4-5 (...) (18 years ago, 7-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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(...) It does happen - if you use more that 2 motors or if you try to use a RC motor. The driver circuit limits current around 500mA, and at that rate it is not long before going in thermal shutdown mode. (...) No, you won't see smoke... RCX motor (...) (18 years ago, 7-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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(...) A rather inventive young man that I know did try exactly that - using the ribbed tubing from the Mindstorms set inside the Mindstorms motorcycle tire. It's a good fit, and a good idea, but I'm not sure how effective it was. (...) One simple (...) (18 years ago, 7-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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(...) I would have expected that compression would be a good thing because it would increase the area of the 'contact patch' - which increases traction - which is a good thing - right? (18 years ago, 7-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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(...) The problem is that this is measuring the static friction ("stiction"). That's the wrong thing to measure if your strategy is to jam all the motors full on and progress forwards (we hope!) with all wheels spinning. To measure the dynamic (...) (18 years ago, 7-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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(...) As you note in your mini-cooper example, *if* you can keep the wheels from "spinning out", but instead are always in rolling contact with the ground, static friction is what's important... and generally, the static coefficient of friction is (...) (18 years ago, 7-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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(...) hmm. This sounds like a good project... (...) All things being equal, I'd put my money on the robot with ten spinning wheels, over a couple (or even ten) stationary ones. I'd also mechanically connect all the motors together, so they drive a (...) (18 years ago, 7-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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(...) Hmmm - that's unfortunate...but if the 'right' strategy is to go with a non-slipping robot, the measurement of sliption is really a lot less important. (...) Yeah - so many of those basic mechanics equations are only approximations - yet they (...) (18 years ago, 7-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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(...) I'll get to that, eventually... there's just too much fun stuff going on, and... (...) A historical point on this. The first time I met Steve was at a sumo event, where I had carefully calculated the correct gear ratio, given the torque of a (...) (18 years ago, 7-Jun-06, to lugnet.robotics)
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| | Re: Newbie needs Help (diff sensor)
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(...) Not so obvious. If you increase the surface the pressure per surface unit decreases proportionnaly (at least on hard surface)... Actually I would expect little or no variation in traction power. Philo (18 years ago, 7-Jun-06, to lugnet.robotics)
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| | Rotation Sensor Accuracy [was Re: Newbie needs Help (diff sensor)]
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Steve wrote on Tuesday, June 06, 2006 5:59 PM <<snip>> (...) <<snip>> I think what is really meant is that most RCX firmware implementations are poor at filtering hardware transient errors. And the Rotation sensor is very "good" at generating (...) (18 years ago, 8-Jun-06, to lugnet.robotics)
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