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Servos and Minibots

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  • Servos and Minibots

    Are we allowed to use servo motors on the minibots?

    Rule B says, "no more than two motors (PN W739083)." Rule A says, "TETRIX components that are not in violation of any other rules." Does B exclude the use of servo motors, because it says only "two motors" (which would mean that under rule A, servo motors are excluded)? (from FIRST team 3256)

  • #2
    Re: Servos and Minibots

    Bump.. I have the same question

    Comment


    • #3
      Re: Servos and Minibots

      Based on my read of the rules and updates, you should not use the servos. Per Team Update #1 they have clarified the use of only two TETRIX DC drive motors.

      Here's what they look like for additional clarification.

      Good luck with your design and builds!

      Comment


      • #4
        Re: Servos and Minibots

        We need to be certain, we have had the same ideas about the rules, but since the rule is ambiguous, we cannot confirm our suspicions. It would be comforting if we had a FIRST official clarify this rule.

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        • #5
          Re: Servos and Minibots

          Has anyone created CAD of the Minibot motors yet?

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          • #6
            Re: Servos and Minibots

            the Tetrix servos could qualify if they do not exceed the 4 watt maximum. The problem is that specs are still not available, and we do not know what specs FIRST uses to determine the watt-rating of a servo. We are still waiting for a clarification from GDC on this issue (see Team Update #3). The main servo mfgs. generally give voltage ranges, torque, amp draw, etc., but not wattage ratings. anyone else have a definitive answer to this problem?
            Last edited by 2011FRC0175; 01-18-2011, 06:59 PM. Reason: Grammar, info

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            • #7
              Re: Servos and Minibots

              Tell you the truth, I still don't see the difference between a continuous rotation servo (CRS) and a motor. Tetrix makes a CRS, it is called a servo and per update #3 we can use as many as we want assuming they are under 4 watts.

              If a servo qualifies as a motor then we could use them to climb the pole but update 1 seems to prohibit that... unless the servo is indeed a motor.

              If it is not a motor, then why have them since the weight penalty for an NXT and added servos seems too pricey to me.

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              • #8
                Re: Servos and Minibots

                I agree the servos do not qualify to help power the minibot climb. My concern is - do they meet the 4 watt limitation and can be used on the minibot in another capacity? If we can't get the specs to verify they qualify, then they can't be used in any capacity on the minibot. If they exceed the 4watt max, that would eliminate their use as well. Without the specs, we can't determine that as well. If FIRST doesn't want us to use the Tetrix servos, they should just come out and say that. Thus, they would eliminate all this discussion, and make the issue clear to everyone.

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                • #9
                  Re: Servos and Minibots

                  The first thing you need is FIRST's definition of 4 watts. Is it electrical or mechanical?

                  If you already have the voltage and amperage specs (it appears that you do from the previous posts) then you can figure electrical wattage easy. In DC, V x I = P. Locked rotor (motor stalled) will always produce the maximum torque. You can measure it yourself by applying voltage without allowing the rotor to turn (DISCLAIMER: this may cause damage in some servos depending on the gearing - attempt at own risk).

                  Most likely what is being refered to is mechanical power (which will be significantly lower in value). If you know the speed that the servo turns at no load and the torque at locked rotor (max torque), you can make an assumption of linear torque (not 100% correct, but very close on small DC motors). Once you have the formula for this line, you can interpolate speed / torque points. With those, you can calculate mechanical power.

                  Since 1 watt is 1 Nm/s:
                  Power (W) = torque (Nm) * Speed (rpm) * 2 * PI / 60
                  or
                  P(W) = T(Nm) * N(rpm) / 9.549297

                  You can use conversions to be able to use any torque units you wish.

                  Comment


                  • #10
                    Re: Servos and Minibots

                    Looks like Team Update #3 R92 B. takes care of the Tetrix servo discussion.

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