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Re: Did I read <R32> Correctly? Six CIMs?
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Re: Did I read <R32> Correctly? Six CIMs?
2 questions related to the number of motors allowed
1) Do you think the rules would be changed to allow a large capacitor across the inputs to the Power Distribution Board to regulate voltage levels? Look at Figure 4-7 in the rules - the capacitor would be hooked across the wires where the text "Power Distribution Board" appears 2) Do you think in the future that they will allow two 12V batteries or larger 12V batteries (automotive instead of motorcycle) to allow for more powered motors? Cheers! -matto- |
Re: Did I read <R32> Correctly? Six CIMs?
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Re: Did I read <R32> Correctly? Six CIMs?
how much weight can a CIM pull? just a quick question..
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Re: Did I read <R32> Correctly? Six CIMs?
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Re: Did I read <R32> Correctly? Six CIMs?
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- Sunny G. |
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Re: Did I read <R32> Correctly? Six CIMs?
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Adding extra motors can be a benefit if you need more torque than was available with the previous CIM limit, but as Al mentioned you might not have enough power available to power that many CIMs anyway. Additional CIMs don't change how much power you can draw from the battery at one time. |
Re: Did I read <R32> Correctly? Six CIMs?
Also on the subject of reading it correctly, are Fisher Price motors in the doghouse this year?
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Re: Did I read <R32> Correctly? Six CIMs?
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Re: Did I read <R32> Correctly? Six CIMs?
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CIM (mini) - 230w CIM (BAG) - 145w RS-550 - 250w RS-775 at 12v - 260w FP 9015 - 190w FP 0673 - 290w Andyprice - 190w And I think that's all the large motors. The FP 0673 is incredibly power dense. The less dense motors are theoretically much harder to smoke (unless you short several through their cases and the frame). |
Re: Did I read <R32> Correctly? Six CIMs?
anyone thinking 6 cim and 4 shorty cim drivetrain geared for ~15mph?
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Re: Did I read <R32> Correctly? Six CIMs?
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Re: Did I read <R32> Correctly? Six CIMs?
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The current of DC motors is approximatley linearly related to the torque applied to the shaft, and is usually assumed to of the form I=k*T. where I the the current and T is the applied torque and k is the "motor constant" (that's what we call it in hebrew, I imagine the name is similar in english). so no matter how you split the torque between any number of motors, the current draw will be roughly the same (if you neglect friction, which isn't always a wise thing to do). If i'm not mistaken, the motor's speed is also approximately linearly related to the torque, but it reduces, for example: w=3000-a*T where w is the rotational velocity. so just like Trent said, reducing the torque on each motor would increase their rotation speed. -Leav |
Re: Did I read <R32> Correctly? Six CIMs?
Nemo,
Here are a few items for your calculations. The internal impedance of the battery is 0.011 ohms fully charged. The #6 wire is 0.0005 ohms per foot, #10 is 0.001 ohms per foot. I am trying to remember, I think Jaguars are 0.004 ohms, Victors are 0.006 ohms. So all you need to do is add up the losses and solve for Ohm's Law. Al's Rule of the Wire Foot (WF) states 100 amps in one foot of #10 or two feet of #6 equals 0.1 volt drop per foot. Starting six CIM motors would max out the current handling of the battery at 600 amps. With a typical FRC robot the wire/foot losses would be 11 (battery resistance) + 2 (four feet of #6)= 13 WF. 13 * 6 (for max battery current) would result in 7.8 volts of drop in the path to the PD. Since the power supply for the Crio drops out at 4.5 volts, this would produce a sufficient drop to reboot the Crio each time the robot started. Predictably, the 120 amp main breaker may or may not trip at this initial start but the temperature in the breaker is certain to rise at that demand. Now all things being equal, the losses in the remainder of the wiring feeding the speed controllers and the motors would prevent maximum stall currents to be reached. However, it is still likely that six CIM motors could under certain circumstance max out the current ability of the battery and main breaker. Teams did report main breaker trips last year with additional motors. My recommendation is to monitor your currents and adjust your design appropriately. |
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