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  • #16
    Originally posted by Dean Hystad View Post

    Partially. To be useful you also have to provide power to the wheel. That's why you use the big turntable. The big hole provides room for a drive shaft.
    Or the medium motor would fit perfectly in the 3-hole slot on the bottom of the turntable gear. Attach the motor to the turntable gear, attach a wheel directly on the front of the motor. Anyway, just playing around with it right now.

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    • #17
      Originally posted by brian@kidbrothers.net View Post

      Give the robot four wheels and it could work like a rear-wheel drive car -- steer the front two wheels, drive the back two wheels.
      Then there's no reason to use the turntables. When you have separate drive and steer wheels the amount you can steer is quite limited. Try to steer any more than 45 degrees and the front wheels begin to slip a lot. You can't get anywhere near 90 degrees. Plus you can't drive sideways or spin in place.

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      • #18
        Originally posted by brian@kidbrothers.net View Post

        Or the medium motor would fit perfectly in the 3-hole slot on the bottom of the turntable gear. Attach the motor to the turntable gear, attach a wheel directly on the front of the motor. Anyway, just playing around with it right now.
        That is a lot of junk swinging around. It would have to be a really big robot. There's also wiring issues. A drive shaft from a fixed motor down through the center hole is definitely the way to go.

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        • #19
          Originally posted by Dean Hystad View Post

          Then there's no reason to use the turntables. When you have separate drive and steer wheels the amount you can steer is quite limited. Try to steer any more than 45 degrees and the front wheels begin to slip a lot. You can't get anywhere near 90 degrees. Plus you can't drive sideways or spin in place.
          You're right -- if the steering / drive system on a robot were set up like a car, it'd probably drive a lot like a... car. :> Doing a quick google search, it looks like a car's wheels can turn up to about 25 degrees maximum.

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          • #20
            Originally posted by brian@kidbrothers.net View Post

            You're right -- if the steering / drive system on a robot were set up like a car, it'd probably drive a lot like a... car. :> Doing a quick google search, it looks like a car's wheels can turn up to about 25 degrees maximum.
            Steering more than 25 degrees works ok, but the benefits from tighter steering are outweighed by packaging issues like using up all the space between your wheels for wheel clearance and having nowhere to put the engine. A while back I did some tests with a three wheel vehicles with a single steerable front wheel. When the drive motor was connected to the rear wheels the vehicle stopped steering when the steer angle was greater than 70 degrees, the front tire just skidded sideways. Less friction in the front wheel and between the rear wheels (there was a differential) would probably allow a slightly sharper turn. When I moved the drive motor to the front wheel it could steer at any angle

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            • #21
              Originally posted by brian@kidbrothers.net View Post
              Give the robot four wheels and it could work like a rear-wheel drive car -- steer the front two wheels, drive the back two wheels.
              Maneuverability might be a problem
              FIRST LEGO League Mentor and Referee/Head Referee since 2011.

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              • #22
                I've contemplated the idea of utilizing the style of drive wheels you would find on a palletjack. I don't see this going anywhere, but it would greatly improve the turning radius compared to an automobile steering style, and minimize "junk swinging around".

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                • #23
                  Originally posted by Dean Hystad View Post

                  A while back I did some tests with a three wheel vehicles with a single steerable front wheel.
                  That's too funny. That's exactly the idea I was thinking of trying, but now that you've mentioned it, if I try it I'm not going to seem very clever! ;->
                  Last edited by brian@kidbrothers.net; 12-21-2018, 01:18 PM.

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                  • #24
                    Originally posted by Tom Mosher View Post

                    Maneuverability might be a problem
                    Right, I might end up having to drive it like a car, using a three-point turn the way you do in a car when you're trying to make a turn that's tighter than the turning radius.

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                    • #25
                      Originally posted by Feral_Goose View Post
                      I've contemplated the idea of utilizing the style of drive wheels you would find on a palletjack. I don't see this going anywhere, but it would greatly improve the turning radius compared to an automobile steering style, and minimize "junk swinging around".
                      I like it. It's part of the fun of EV3 robots -- completely different configurations can be attempted! On my son's robot this year, he switched the wheels so they were in toward the middle of the robot, which resulted in three things:
                      1. A very compact design
                      2. An extremely tight turning radius
                      3. The ability to attach the wheels on both sides, meaning the axle went from the motor on one side, through the wheel, to a hole in a common triple beam between the two wheels
                      Because the wheels were held in place on both sides, the robot was extraordinarily solid, and he added some extra bracing that meant the robot felt like a tank (without being terribly heavy). And the tight turns were fun and super-quick. The main drawback of the design was that it was harder to drive straight, since any slight variations in heading were magnified by the tight turning radius. It definitely resulted in some good learning for him, since he discovered all designs have their pros and their cons.

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                      • #26
                        I would love to give credit for this idea, since it isn't mine, but I don't remember where I saw/heard this...

                        One large motor driving all 4 tires -- all connected together so the robot cannot drive any way except straight. One other motor in the center of mass that lifts and turns the robot in place -- lowers a pad of some sort until it contacts the table and lifts the robot completely into the air, turns a specified amount, and then raises the pad back up. Then the robot continues driving in a straight line in the new direction. Doesn't seem very practical for FLL, but another fun idea to play around with.

                        If you've seen this elsewhere, please post back to give credit to the right person.

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                        • #27
                          Originally posted by Tim Carey View Post
                          I would love to give credit for this idea, since it isn't mine, but I don't remember where I saw/heard this...

                          One large motor driving all 4 tires -- all connected together so the robot cannot drive any way except straight. One other motor in the center of mass that lifts and turns the robot in place -- lowers a pad of some sort until it contacts the table and lifts the robot completely into the air, turns a specified amount, and then raises the pad back up. Then the robot continues driving in a straight line in the new direction. Doesn't seem very practical for FLL, but another fun idea to play around with.

                          If you've seen this elsewhere, please post back to give credit to the right person.
                          Seen it done a couple times back in the RCX days. A similar solution was to have two motion platforms, one for driving N/S and another which could be lowered into position for driving E/W. I don't remember how the second platform was moved in and out of the driving position. Driving straight was a big challenge back then, now it is easy. A lot of things in FLL are too easy, and this has the side effect that the things that should be easy end up being quite difficult. For example, if you couldn't drive straight for 10" you would never consider driving all the way across the board to catch the lander or position the satellites. Now you can write a program to do exactly that, but it does not run reliably. Because you never had to deal with how to make the robot get somewhere when you can't depend on driving you don't have any tools for fixing navigation problems.

                          The development cycle in FLL has done a 180. Back with the RCX it was difficult to do anything. When the robot could finally score points the mission was pretty reliable because you had already done all of the hard navigation work (using walls and lines and picking paths that didn't require many moves). Now with NXT or EV3 you can write a program to drive over to catch the lander and have it working in an hour. Unfortunately it takes weeks to get the mission to be reliable. The RCX schedule was a lot more satisfying because the success followed the frustration.

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                          • #28
                            Originally posted by brian@kidbrothers.net View Post

                            That's too funny. That's exactly the idea I was thinking of trying, but now that you've mentioned it, if I try it I'm not going to seem very clever! ;->
                            Not doing something because it's already been done is too limiting. I built three wheel robots, but I didn't invent three wheel robots. I think I remember seeing three wheel robots in the Ferrari brother's book. With a lot of stuff I was just too ignorant to know that it had been done to death before. Knowing it had been done before didn't make it less fun or educational.
                            Last edited by Dean Hystad; 12-28-2018, 03:49 PM.

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                            • #29
                              Originally posted by Tim Carey View Post
                              It's not Into Orbit related, but last year I had my kids program the robots to dance. 30 minutes of programming and then a dance party. It looked terrible having the robots try to "dance", but the kids had a blast.
                              This was a big winner!!! The kids had so much fun!

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                              • #30
                                Glad you and they enjoyed it!

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