Is two falcon500 with lower ratio gearbox better than one falcon500 with higher gearbox?
I usually see that great team use first one, but I don’t know why.
It really depends on what you’re trying to do.
The only benefit in adding two falcons together is increased torque.
Maybe you can specify if you are referring to drive trains or other mechanisms.
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I want to use it on elevator or arm.
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Some general reasons for each option:
2 Motor Low Reduction:
- Increases input power, enabling greater potential acceleration and typically higher top speeds
- Tentative redundancy, if one motor becomes disconnected the other may be able to pick up the slack in certain scenarios.
1 Motor High Reduction:
- Only uses one motor and PDP slot, may reduce cost and simplifying electronics.
- Finer speed/position control without fancy closed loop control. May be preferred if running dumb control
Note how all of these reasons have a ‘maybe’ or ‘potetial’ clause. It is truly difficult to select the best method without intimate knowledge of the end use case. You wouldn’t but a semitruck power train in a small van, even if there are numerous advantages in theory. Neither option is inherently better than the other, and must be considered in the context of the rest of the robot and how it intends to function.
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I see. I saw that Finer speed/position control without fancy closed loop control. And, we are not very good at program(You can see us as rookie team). Due to that, do you recommend us just use 1 motor?
Sometimes it’s better to have the extra power and not need it than to need the extra power but not have it. We trust our math to get us close, but for some mechanisms, you like to KNOW you’ve got enough to get the job done. It’s so much easier to throttle back the power/speed in code, or trade out a cartridge on a planetary gearbox, than it is to retrofit another motor onto an under-powered mechanism.
But also remember that with great power comes great responsibility. Gotta make those mechanisms robust. We gave our arm enough power to destroy itself this year, and it took the opportunity to do that twice, lol.
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You can still get the finer control from two motors, it comes from the high reduction gearing. If the mechanism moves inherently slower, and smoothing some motor weirdness due to torque curves, its going to be easier to control.
If selecting for an elevator or arm, it can help to over-gear and over-power then work backwards from there. An intake wheel or deploy may be better suited to low gearing due to the need for speed, and the easier backdrive may save the gearbox on impacts.
To give my one and best suggestion for a rookie team, it’s to take your best educated guess then test and iterate from there. Optimal Motor and Gearbox selection can come from maths and/or intuition later on. Also, Similar to what Andy said above though, better to have a slow and robust mechanism than a fast but broken one.
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Thank you! I will remember that.
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Something people haven’t touched on yet is current draw. With more motors and less mechanical advantage, the two-motor gearbox will draw more amps than the gearbox with one motor and greater reduction. Whatever the difference in ratios is, that’s the difference in total current draw. (A system with two motors at 1:1 will draw approximately twice as much current as a system with one motor at 2:1.) This is the cost of higher output power: greater input power is required, as well as design and operation to safely handle that power.
Definite downsides to increased current draw:
- shorter battery life during practice and programming sessions
- depressed system voltage, sapping precious power from all other motors
- hotter wires and connectors, increasing resistance and decreasing power available to the motors
Possible risks from higher current draw, which should be understood and mitigated or avoided:
- browning out, which causes temporary loss of control of the entire robot
- tripping the main breaker, which lead to loss of control for the remainder of the match
- greater probability of future breaker trips after each time they are tripped (until replaced)
- fire from overheated connectors or melted wire insulation
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There’s no one right answer to this – it’s all a question of tradeoffs.
Having two motors with a lower ratio on a climber will generally allow you to climb faster than if you had a single motor with a higher ratio. But, you get that at the cost of added weight, cost, additional current draw and higher complexity.
In games with climbing end-games, it’s common for the “Great teams” to be running around the field trying to score until the last few seconds of the match, when they rush into climbing position. So, they need a climber that gets them to where they need to be in a matter of a few seconds. A lot of other teams might take a different strategy and start climbing 30 second before the match ends.
The other thing to think about is that speed of the climber isn’t the only concern – a fast climber doesn’t do you as much good if it takes you 30 seconds to actually connect to whatever you’re climbing.
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I hear that you might be concerned about the complications of trying to control two motors vs just one.
This is NOT the case. Once both motors are mechanically installed and wired up There are only a few extra steps to get them ready and after these then the code can treat them as one output.
With most gearbox configurations the motors will be in phase meaning that a positive command outputs the same rotation so no invert configurations will be needed.
Go to CTRE examples for the TalonFX devices and look through the multiple bits of code. GitHub - CrossTheRoadElec/Phoenix-Examples-Languages: HERO C#, FRC C++/Java, future platforms. You might find an example that closely matches your mechanism. In many cases these code examples will only have one motor but you will see the drivetrain examples you will see in the robotinit that the second motor for each side is set to follow the master motor. You can apply this same “follower” logic to any of the other examples that only utilize a single motor.
I am a big fan of the MotionMagic examples and I have a few Youtube videos on how to use them on our JUMPSTART robotic channel along with many more hours of how to FRC from our teams.
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I saw those codes, and it’s really useful, thanks.
However, I don’t find your videos. But I will keep searching.
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