Are spark maxes supposed to stay in brake mode when powered BUT not enabled? Our team powered on our robot for the first time yesterday, and our arm has to stay upright to fit inside the frame perimeter, and to zero the arm motor, but after we turn it on and release the arm it wants to fall towards the ground. Right now we are using rev NEO brushless motors9(Not 550s) and the standard REV Code provided through their 2024 kitbot. Any help would be appreciated, thank you.
Can you give us more mechanical details? Is the motor just attached to the arm directly or are their gears in between? If so what ratio? I can’t think of a single motor out there strong enough for an arm without gears/chain reduction involved somehow.
My guess is the motor on its own is not anywhere near strong enough to hold the arm still with brake mode only. You need more torque (if you do have a gear ratio it needs to be higher still). If it’s also not geared down it will be very fast and hard to control
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For our gear boxes we are using two 5:1 ratio gearboxes, I’m not the best at the mechanical aspect of the robot, so I linked the set up we used for our whole arm.
5:1 will be “weak” by most standards. If the two 5:1 were planetary and combined to 25:1 that’s better but still pretty low
Would be good to know the length of the arm or the distance to what’s called the center of mass from the rotation point (likely the end of your arm) and also how heavy the arm is.
Then you can use a tool like
And find what ratio will work for what you need to do.
5:1 tested will not move a 15lb arm with a 20" CoM. That’s the default arm size it has
I’ll look at the arm once we’re inside of the center building again, thank you for the help!!
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No problem, did add a note about combining the gears, didn’t notice how the two 5:1 were already being mixed. 25:1 can move the default arm, but not well. It also estimated 5 seconds to move 90 degrees. Changing to a 100:1 actually brought the time down to 0.4 seconds because it’s not struggling to get there. Might want to look at changing to 10:1s for each stage if possible.
If you can’t change those gearboxes then you could use external gears or a chain reduction to get another 4:1 or 5:1 and be in a better range. It really depends on the length and weight of the arm.
Are you setting brake mode via code or by pressing the button on the spark max? If you set it via code I think it waits until the code starts up to enable brake mode
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if brake mode has been burned flashed to the sparkmax, then yes it will enter brake mode immediately once powered up. If the arm is still falling it may be because their is not enough damping from the brake mode. You may need a larger gear reduction if this is the intention of your design, or make use of a larger motor such as a NEO or Kraken which have much higher braking capability.
We have the braking mode set for when the robot is turned on through the spark max. We are also using the rev NEO not 550 for the arm motor.
At the moment we don’t know what is going on
The motor is the standard rev NEO brushless not the 550. Right now we are working out an issue where our swerve drive isn’t working. We’re getting it done though
REV doesn’t have a 10:1 stage (and I probably wouldn’t use it if they did since itll likely have the same load issues the high ratio Vex planetary gearboxes did). They do have a 9:1 which is new this year, but I’m still hesitant. Best bet would be to add a 3rd stage with 4:1 if you’re going for 100:1 total.
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We have only just started to use the REV max planetary (part of max swerve), I’m just familiar with the banebots 100:1 (prefered) and the VP 10:1 I agree they can bind. That’s why maybe an external chain reduction would work too. Also would help if the arm is on a dead axle
Okay so I found the issue with the arm. Our batteries were operating at 80 percent and causing it to slowly sink to the ground after we fixed our wiring. Right now we’re figuring out exactly why our arms encoder values are wonky
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