 | | Adder/Subtractor revisited
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I'm a little confused again. The explanation of the adder/subtractor was to allow one to power each wheel while the differential compensated for the different motor tolerances, allowing the bot to travel in a straight line. Clear as a bell, until I (...) (25 years ago, 31-Jan-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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Reno, no the purpose of the adder/subtractor is to supply power to two outputs based on the differential between two inputs. So if you have two inputs (A, B) and two outputs (X, Y), you get the following equations for rotational velocity (of course (...) (25 years ago, 31-Jan-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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(...) Nope. That's what one single differential does. Use two motors to power the two axles on the differential, then use the rotating differential body to drive your bot. Regards, Johannes. (25 years ago, 1-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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This is not what we did with our models. In the method we, and others have used, you apply the motor power to the carriers of the differentials. There are two possible places to apply the drive force to each carrier (24 teeth or 16 teeth). You do (...) (25 years ago, 1-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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(...) Right. This is what I was trying to get at. If one motor gives too little power, you can add the power of two together trough a differential. Power the axles of the differential by two different motors, and the added power comes out through (...) (25 years ago, 2-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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Ahh, I see. I thought you meant to power the primary diff in the A-S transmission in this fashion. Yes, a third diff coupled carrier-to-carrier with the primary one in the A-S would work. Three diffs ! I don't think I have enough of them to model (...) (25 years ago, 3-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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(...) 5229 is your friend :) Jasper (25 years ago, 3-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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(...) I can understand why you'd need a method like this if the two motors were radically different types, but if you're dealing with two identical motors (such as the 9V MindStorms motors), is this really necessary? The tolerances may be a teensy (...) (25 years ago, 4-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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Well, I don't know about your experiences, but I have had tracked vehicles with identical (as much as possible) construction on each side of the vehicle that deviat several degrees for each foot travelled. This was due to the characteristics of the (...) (25 years ago, 4-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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In article <36B6F795.4B9310A6@n...a.kth.se>, johannes@nada.kth.se says... (...) Ingenious as it is, this thread and previous similar ones have pointed out the primary problems with the A-S drive approach: power transmission through the LEGO (...) (25 years ago, 6-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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That sounds very interesting. I hope to see some diagrams or photos soon... Your approach solves the biggest problem introduced by the A-S drive, that of insufficient torque when driving tracks. Two motors is the way to go for tracks. -- SeeYa ! (...) (25 years ago, 6-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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In article <F6psw8.Bxy@lugnet.com>, cyberia@erols.com says... (...) Yes, this is the feature that really worked out well. By changing one gear (and adding appropriate number of 1/3 thickness shim plates under the motor), one can get the following (...) (25 years ago, 6-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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(...) Actually, I've had pretty good luck with independently driven left and right drive trains; I haven't had a lot of problems with robots curving when I want them to go straight. I find the adder/subtracter useful for a different reason: it makes (...) (25 years ago, 6-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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(...) Here's what I do and it works quite well. I have added a "partial duty cycle" mode to my motor control system. Basically I intermitantly turn off the motor for a very small increment of time. The time-average of a properly synchronized (...) (25 years ago, 7-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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A nit, but you meant 75% duty cycle, no (or reversed your terms) ? -- SeeYa ! ---...--- Jim ---...--- Hello... Is this thing on ? David Harry wrote in message ... (...) (25 years ago, 7-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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(...) [snip] (...) I actually had already tried that, and couldn't get to work in these particular circumstances. I couldn't get the robot to turn off the motor for any period briefer than 50 ms, and even that short a period (coupled with setting (...) (25 years ago, 7-Feb-99, to lugnet.robotics)
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| | Re: Adder/Subtractor revisited
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There is a company in Chicago that does a lot with small motors; it's named Bodine Electric, and of course they have a web site at (URL) I can tell the motors in the RCX sets operate with pulse width modulation to control power. Bodine's site gives (...) (25 years ago, 7-Feb-99, to lugnet.robotics)
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