We are currently in the design process of our robot, and needed some help in deciding what RPM we should use for shooting the discs. What RPM are you guys using, or what’s the most appropriate RPM to use for this season’s flywheel?
1 Like
I am using a 7:1 ratio (4200 rpm) at around %70 power
Another great option is following the engineering design process! 
Prototyping a flywheel and testing the performance of different gear ratios not only results in a better end result, but also looks great for the engineering notebook.
7 Likes
There is a search bar for your convenience. Welcome to the forum.
7 Likes
What do you mean by 70% power? Like 70% velocity? 4200 * 70% = 2940
5:1 600 rpm = 3000 rpm
2940 < 3000
wat?
6 Likes
I am talking about %70 for shots from the match loader at full air sorry for not clarifying. As we run out of air throughout the match or go farther away from the goal we will need to increase power which is why it is helpful to use a 7:1 ratio. Another reason is that running the motors at close to %100 puts a lot of stress on them.
1 Like
You keep saying you’re going to run your motors at %70 power. There are two things wrong with this:
- You write %70 when it’s supposed to be 70%. We aren’t talking about $ here.
- You keep saying power. It’s speed. When you gear for speed, you lose torque and gain speed in proportion so that your power remains constant. When you write in the code
motor.spin(70, percent)you lose speed but don’t gain torque, and therefore you have less power. However, you don’t know how much power you lose, since I believe when you artificially slow your motors you also lose torque.
Please start saying you’re going to run your motors at 70% speed.
10 Likes
Wouldn’t power and speed both make sense here? I am running the motor at 70% of it’s power which is also 70% of it’s speed.
1 Like
I will tell you straight as someone who has been in the room - when you make a performative EN, it is obvious to the Judges. Might as well not do the notebook if its only smoke and mirrors. Do the notebook in order to make better design and team management decisions. If the notebook is genuinely helpful for your team, the judges will be impressed.
12 Likes
Not necessarily, percentage usually isn’t linear, at least in vexcode. Don’t have the graph but there’s a graph that correlates it.
1 Like
Am I right at thinking the motor has more torque at 50% than 100 too? So the recovery rate to maxpeed would be faster this way(even tho its not max).
No, reducing the speed in software doesn’t add more torque.
5 Likes
The motor power is how powerful you want your motor at 100% the motor will spin at full power and spin at top speed. You can change the speed or torque of the motor with gearing and the gear Cartridges .
1 Like
in fact, reducing the speed through software in my experience actually decreases the torque as well. So by reducing speed through software, you are really cutting down your power from both ends, speed and torque.
7 Likes
When I go into my devices on the brain and run the motro from there it provides you with a graph showing torque in Nm. When the motor is at 50% is when it shows the highest amount of torque. Am I understanding this wrong?
I don’t know what the brain is doing but motors use electromagnets to turn. The percentage of power is the percentage of possible electricity the motor can use . So at 50% the magnets are at 50% strength which means the motor is at about 50% of top speed and has 50% of possible torque
1 Like
the X axis is the speed and the torque increase and the rpm or speed decreases and the power output is on the y axis
The thing to remember when looking at motor torque-speed curves, is that the axis showing speed is not the speed you are commanding the motor to run at, it’s the speed the motor is running at due to increased load. Here’s are the original theoretical curves we calculated for the old 393 motors many years ago. (which is drawn differently from the V5 curve above).
It gets more complicated with V5 motors, generally you are asking the motor to run at a requested speed and it is using closed loop control to try and maintain that speed, internally the motor will increase current (and therefore torque) as necessary until we hit the current limit (which may be reduced as the motor heats up). When using raw voltage control, it will behave more like the old 393 motor except we still impose current limits, that’s why the blue and green lines on the V5 graph become horizontal.
9 Likes
3600 rpm direct drive.
5 Likes