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Did I read <R32> Correctly? Six CIMs?
It seems we can now use six CIMs, or am I reading something incorrectly?
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Re: Did I read <R32> Correctly? Six CIMs?
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Re: Did I read <R32> Correctly? Six CIMs?
I had trouble believing that as well. Awesome!
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Re: Did I read <R32> Correctly? Six CIMs?
Unless there was a typo, and until an update comes out, there are 6 CIMs usable, as well as 4 Bag CIMs or MiniCIMs!
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Re: Did I read <R32> Correctly? Six CIMs?
Please read the blue box following the motor list very carefully. Running many high current motors is a risky choice. CIM motors stall at 133 amps.
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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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And that's not including any of the 24 other motors you're allowed to use. |
Re: Did I read <R32> Correctly? Six CIMs?
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For example, 6 CIM motors on the drive train gives you more torque at your disposal, thus reducing the risk of stalling them. Each team has to do the math to determine what it optimal for their design. |
Re: Did I read <R32> Correctly? Six CIMs?
For Al (and all you electrician magician), does appying the same torque to two CIMs or three CIMs draw more current? Although three CIMs would distribute the current over more breakers, I suspect they would draw more current over all. If teams are going to be traction limited in low gear anyway, is it worth it to go with three CIMs in the drive?
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Re: Did I read <R32> Correctly? Six CIMs?
My suspicion: You'll see a bunch of designed-for-6 motor drives, with 4 motors populated by the competition as teams need the weight and energy elsewhere .
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Re: Did I read <R32> Correctly? Six CIMs?
I'm suspecting that Banebots' 256:1 CIM gearboxes may become popular in a day or two.
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Re: Did I read <R32> Correctly? Six CIMs?
I have an earnest desire to estimate how much our battery's voltage will drop as a result of a given amount of demand by the motors. How does one do that?
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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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Re: Did I read <R32> Correctly? Six CIMs?
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As for the 2 vs 3 CIM Motors, correct me if I am wrong, but based off of this http://content.vexrobotics.com/docs/...otor-specs.pdf 2 Motors at 300oz-in each will draw about 115 amps a piece. 230 amps total. 3 Motors at 200oz-in each will draw about 75 amps a piece for 225 amps total. Because the curves are linear, total current draw shouldn't matter on number of motors. However, the motors will be rotating faster on the 3 motor setup at ~2200rpm compared to around ~700rpm because each motor has to put out less torque. |
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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- 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. |
Re: Did I read <R32> Correctly? Six CIMs?
Al,
That's very helpful - thanks very much for posting. |
Re: Did I read <R32> Correctly? Six CIMs?
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Re: Did I read <R32> Correctly? Six CIMs?
Aldaeron,
It is unlikely that two batteries will be allowed. Batteries are not happy when connected in parallel when they don't match in characteristics. The manufacturers frown on this practice unless the batteries have been installed together and charged together from the beginning. Systems that use batteries in parallel often use Schottky diodes to isolate the batteries. However, we would need two 600 amp diodes at $100 each. The diodes would drop about 1 volt. Let us not forget that adding an additional 12 pounds is significant in our competition as well. Teams are already struggling with the 150 pounds most robots achieve. I fear we are stressing our participants with lifting these weights throughout the season. |
Re: Did I read <R32> Correctly? Six CIMs?
Last year, I said "22 motors? Challenge Accepted."
30 motors? Not even going to try. |
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Carbon aerogel super/ultracapacitors. Also, these things are dangerous. |
Re: Did I read <R32> Correctly? Six CIMs?
I was not thinking of a six motor drivetrain, but a four motor drivetrain and a CIM for the disk launcher.
The sixth CIM? I dunno, maybe a big defense fan? :rolleyes: |
Re: Did I read <R32> Correctly? Six CIMs?
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Re: Did I read <R32> Correctly? Six CIMs?
I didnt read most of the posts but is there a limit of how many motors or motor controllers a bot can have this year.
Thanks team 3633 |
Re: Did I read <R32> Correctly? Six CIMs?
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