Motor Choice for Flywheels

I’ve been following the threads discussing wheel choice and gear ratios for flywheels. We tried a dual flywheel with motors with turbo gears and a 7:1 external gear ratio, based on a few posts and videos. We haven’t been successful at launching full field shots. The consensus seems to be needing to have a overall gear ration somewhere between 22:1 and 28:1. There are a lot combinations to get there.

Is there any advantage to a specific internal gear ratio for the motors - torque vs speed vs turbo?

Try to use turbo motors. It reduces the risk of build error. This may also reduce friction. Also try to achieve the lowest possible gear ratio that will shoot into the high goal. This will increase the amount of torque(power) the flywheel has to spin back up to speed when the ball is shot. This subsequently will increase acceleration.
I hope this helps

Thank you for the advice. We’ll try adding in a 84:60 (7:5) set of gears. That should be the fastest change and would get us to 23.5:1

no problem. no problem at all

Keep in mind the wheel size will also impact your performance. Larger wheels will have a larger tangential velocity at the same RPM, but will also require more power to be kept spinning. Therefore, if you’re using smaller wheels, you’ll need a bigger gear ratio, while larger wheels won’t need as big a gear ratio.

help, how to connect to 12 motors in the cortex, if you only have 10 output?

There is a product called the y-cable. This branches off like a “y” allowing you to put 2 motors to a single port. You will need 2 for 12 motors.

To add something that relates to the thread: More mass to the flywheel equals less slow down and more time to spin back up to max speed, so there is a balance challenge there.

You can also use a power expander, which requires an extra battery but allows you to hook up to 4 motors (and more with y cables :slight_smile: ) to a single port on the cortex.

My advice, dont go over the top, I know a team that was running their motors at 65 power and was still overshooting the goal :).

Correct me if I’m wrong, but I don’t think it’s legal to have more than two motors controlled by the same port.

You are correct. A power expander occupies one port for each port on the power expander that is being used. A full power expander, therefore, occupies four motor ports on the Cortex.

I’ve never actually used a power expander before, but from my understanding wouldn’t it be possible to y off of a cortex motor port to two power expander ports and then y again off of both of those to control 4 motor ports?

The rule you quoted simply refers to using two y cables on the same port, which is illegal. Im pretty sure its legal to y off of a port on a power expander. Not to mention I was wrong anyway :slight_smile:

Whoops! you are right, the power expander uses one port on the cortex for each motor it controls :slight_smile:

Something that may be a good idea is to y off of a vex cortex motor port (or 2) and connect the plugs to the ports on the power expander, then connect a flywheel (or similar) to the motor ports on a power expander, this ensures that the motors receive a constant voltage and you can monitor the voltage of the flywheel individual to the rest of the system through just 2 cortex motor ports (and a analog port).

Possible, but not recommended :slight_smile: It will also be illegal because the power expander is essentially a passthrough with a dedicated battery. It would be the same as connecting a y cable to another Y cable.

Where does it say that in the rules though? R12 says you can’t y off of a cortex motor port or a power expander port, but I don’t see why you can’t do both (not that you’d want to).

Well R12 States that a maximum of 1 Y cable may be used per motor port on a microcontroller. It then goes on to clarify and say: “You cannot “Y off a Y” to have more than two (2) motors controlled by the same Motor Port.” Making plugging two Y cables into a single port illegal regardless of the existence of a power expander.

Hi Chris

Our guys are running a configuration of dual 5 inch flywheels with 3.5 inch gap between the wheels, running 4 motors with turbo gears through 1:7 ratio. They achieve full field shots into the high goal using only 47 motor power.

If this configuration does not work for you, please ensure that all your axles spin by hand with ease before fitting any of the gears or connecting the motors to them. If they do not spin freely, you are going to have a bad time. To get them spinning freely, check your fly-wheel assembly is square (not skewed) and that your axles are perfectly straight. If the axles are still tight, then use a round file to clean out the bearing hole.

Thanks Torqueative. We are also using 5"m wheels and the 3.5" spacing, but only 2 motors. Everything did spin freely. At our last practice they did get the additional gears in place and were able to check each side independently but we ran out of time before we could fully test the launcher. I’m really excited and anticipating our next practice to see how they do.

Okay, that makes sense now. That was what I thought. Thanks for clarifying.

One more idea to bounce off before your next practice: make sure that in the code you set each motor to a “turbo” 393 motor rather than a 393 high speed motor or 393 motor. In our testing, holding all else constant, the turbo motor setting gave the output shaft more torque. This is quite strange, (a dishonest team could set all 10 motors to turbo motors to get more torque everywhere), but it does make a pretty big difference, both in the power of the shot and the time it takes for the flywheel to get back up to speed. Hope this helps.

Hate to burst your bubble, but setting a motor to turbo does not give a motor more torque. That option is simply so that when using integrated encoders the program will know how many “ticks” it should see per output revolutions of the motor.