Flywheel Ball thrower for ALB

Created a prototype flywheel ball toss. Works well but the two motors 393’s overheat very fast. Anyone have an option to flywheel or how to solve motors overheating? Will 4 motors help or is it in the gearing?

I also made a flywheel…

I used 4 motors and it takes a little while for it to burn out the motors. What internal gearing are you using? Speed internal is what Im using

What gearing are you currently using? Internal and External. Inherently 4 motors at the current gear ratio will overheat slower than 2 motors but depending on the gear ratio 4 motors still might not solve the problem.

Under what conditions are they overheating? Are you shooting one ball after another? or are they overheating just running without even shooting any balls?

Make sure all your axles can spin freely without substantial friction. With the motors disconnected, your gear train should be able to continue spinning freely for, oh, about 15 seconds or so, I think. Bent axles or misalignments can cause you problems. Keep in mind that any friction present at the flywheel end of the gear train will effectively be “magnified” from the “point of view” of the motor. These flywheel gear trains are somewhat sensitive to small errors in assembly, friction of any kind, and misalignments of the frame that contains them. Things that you might be used to getting away with under normal circumstances might not work under these geared-up conditions.

We built another prototype last Saturday, single wheel shooter powered by two 393 motors. They were overheating in perhaps 2 minutes. One difference in the way we will be using these motors this year is that they will be drawing continuous power. The lift systems and, to a lesser extent, drive systems of the past are used intermittently in shorts bursts. Power management for these motors may be tricky.

Mind if I ask how you had this geared? What was the internal gearing set at? torque mode? high speed? turbo? I’m wondering if that makes a difference.

We used 393 motors with speed gears (160rpm) followed by 25:1 and later 20:1 gearing. The single wheel was running at a theoretical max of 4000 and then 3200 rpm. Obviously it ran slower, balls were consistently hitting a target area of 10x10 inches at 10 feet from the shooter and high goal height.

The important figure is the speed of the motors, these were not encoded so I don’t know the actual speed but would assume they were 60 to 70% of free speed, this is about the limit for the PTCs.

We made a 2 motor 7:1 gear ratio with internal turbo gearing, We haven’t had any problems with overheating even after running for four minutes without stopping.

That’s what we are running but with 4 motors. 2 motors is enough? I’ll have to look mine over and remove any more friction I can because when it’s only running on 2 motors it burns out relatively fast.

how much of a difference would having your motors torque high speed or turbo geared

There is a gearing chart on this page:

Basically, the “normal” (aka “torque mode”) 393 motor will output a max of 100 RPM at zero load. Also at zero load, the “high speed” option would output a max of 160 RPM. And at zero load, the “turbo speed” option would provide a max output of 240 RPM. But notice how the stall torques change. You don’t get something for nothing by using the higher gears - your motors can stall a lot easier at those speeds. And don’t expect your motors to actually run that fast: as soon as you attach them to the kind of gear train necessary for running these flywheels, the accumulated friction, etc. will bog them down quite a bit.

try two motors geared internally for turbo speed, and gear externally 1:9, also use the biggest wheels you have :slight_smile:

why are people always using the 5" tires? im thinking of using 2 4" high traction tires on either side to allow for more adjustment. also seems like it would give a more consistent throw and give the ball more of a guide and up to double the traction to the ball.

her is an inventor file…
High Traction Tire 4 Thrower.iam (1.19 MB)

I also designed a 2 motor 7:1 externally and turbo internally and at the correct angle it will launch into the high goal from the starting tile. The only problem is that the wheels are not in sync causing the ball to move too much to the right or the left. I am going to try a 25:1 correctly synced with 2 speed motors.

One reason is for the calculation of rotational energy, (1/2)Iw^2, the moment of inertia, I, is equal to aMR^2, where a is dependent on the distribution of weight in the object, M is the mass, and R is the radius of the object. With a 4" wheel, R^2 is only 16 times that of a 1" wheel, while it is 25 times larger with a 5" wheel. In order to reach the same amount of rotational energy of the 5" wheel with the 4" wheel, you would need a significantly higher angular velocity, leading to a higher gear ratio, which may cause motors to burn out more quickly.

If you can make it work with the 4" wheels though, that would be great to see, but the rpm required might be more than the vex motors can handle.

When viewed from the standpoint of pumping energy into the ball, I can see what you’re saying. But if we assume that the ball is leaving the shooter at a velocity that is equal to the tangential velocity of the wheel, then doesn’t that require you to run a 5 inch wheel at a somewhat slower rpm than a 4 inch wheel (because of the difference in circumference)? And because you must run a 5 inch wheel slower than a 4 inch wheel, the angular velocity of the 5 inch wheel is therefore also slower, thus causing the rotational energy to be lower than it would be if it were at the same rpm as the 4 inch wheel?

I’m just wondering if the two effects (increased angular momentum vs. slower rate of angular velocity) might somewhat cancel each other out???

After a bit of testing ourselves, it seems to me that angular momentum is a bit more important. When balls are ‘launched’ you can clearly hear how much the flywheels slow down. The more momentum you have it seems like there will be a better transfer of energy. The motors alone do not have enough power to really launch the ball…that stored energy (momentum of the flywheel) seems very important.

(I have no scientific reason for this thought…just my initial thoughts from our practice today and getting some relatively successful launches)

Okay, just to be clear: I’m not saying that the angular momentum is not important. I’m just asking about the fact that to reach a particular distance (for a given angle), the ball must exit the shooter at a particular velocity. Presuming that the ball’s flight velocity matches the tangential velocity of the wheel, then I’m thinking that the 5 inch wheel will need to be spinning at a slower rpm than the 4 inch wheel simply because the 5 inch wheel has a larger circumference. A slower rpm for the 5 inch wheel means a slower angular velocity, which means its rotational kinetic energy will be lower than it would be if it were spinning at the same rpm that a 4 inch wheel would need to be spinning at.

I’m not saying that the effects cancel out exactly, but I’m wondering if the 5 inch wheels are really worth buying if you already have 4 inch wheels on hand. The actual difference in rotational energy might not be so big, after all.

The velocity of the ball after exiting would not match the angular velocity of the flywheel, because the mass of the ball, m in 1/2 mv^2, is less than the value of I in 1/2 Iw^2. Therefore, the exit velocity of the ball depends on both the angular velocity of the wheel and it’s moment of inertia.

With the 5 inch wheels, you can get the same amount of rotational energy as the 4 inch wheels on a lower rpm. Additionally, the 5 inch wheels would have a greater angular momentum, which is found by a M R^2 w, where R is the radius of the wheel, M is the mass, a is a constant for the moment of inertia, and w is angular velocity. The larger wheels not only allow for a lower required angular velocity, but also have a higher angular momentum than 4" wheels running with the same amount of rotational energy.

Personally, I would say it is worth it to get the 5" wheels for this year’s game, though I would like to see how well a 1:15 geared launcher on 4" wheels would work.

I agree with you there… but…

To me, this part seems a little bit like comparing apples and oranges. The velocity of the ball is measured in units (m/s) not the same as the angular velocity of the flywheel (rad/s). Similarly, the mass of the ball is measured in units (Kg) not the same as the angular momentum of the flywheel (kg m^2/s).

Perhaps you meant to say “The velocity of the ball after exiting would not match the tangential velocity of the flywheel”? If so, that would mean that there is some significant slippage taking place between the ball and the edge of the flywheel. That’s possible, I suppose, but then we would need to make some measurement or guesses as to how much it slips. I presumed the slippage is zero with both the 4 inch wheel and the 5 inch wheel and that the ball is not made to spin. But if slippage or spin is not the issue, then I’m not sure how the velocity of the ball after exiting would not match the tangential velocity of the flywheel. If no slippage is happening, then at the instant of release, I think the ball’s linear velocity would match the flywheel’s tangential velocity. If that’s not case, maybe you could explain how that happens.