Shooter gear ratios

Alright so on our current nothing but net shooter we use two 4 inch wheels with each being powered by a 7:1 gear ratio with turbo motor. The ball is shooting alright but its not the distance and height we want. Do you guys have any suggestions on what gear ratio would work the best and with what type of motor? Any suggestions are greatly appreciated :slight_smile:

I believe that a 1:7 4" wheel double flywheel with turbo motors should be capable of launching full court. The angle should be adjusted so that the ball reaches the height you desire. The problem may be that the flywheels aren’t reaching the desired 1680 RPM. I would make sure you have solid construction using bearings, and check if the wheels can spin freely without the motors attached. There are rare instances in which the holes for the c-channels and plates are off by a few millimeters, in which case the shaft will move chunkily (chunk-like). Grease the insides of the motors, as that may be a factor.

We purchased a tachometer to measure the RPM of our flywheel. It only cost about $6 or $7, and doubled as a laser pointer (not a very precise pointer, though :D). It helps out when you are building your flywheel and want to see if it’s actually going at what it’s supposed to go at.

I’ll add a link when I find the cheap one we have.

EDIT: Well, it was $15, I guess: http://www.amazon.com/AGPtek®-Professional-Digital-Tachometer-Contact/dp/B004Q8L894/ref=sr_1_1?ie=UTF8&qid=1445979728&sr=8-1&keywords=tachometer+rpm

It’s possible, but I have not seen a lot of robots with 4" wheels, less than 4 motors and a shooter that goes full court.

This team has a 4" wheel with six turbo motors and a 25:1 gear ratio.

If you like that design, then you should definitely go for it. We just weren’t willing enough to use six whole motors for just the flywheel. :stuck_out_tongue:

Our team had the same problem- 4" wheels, 7:1 gear ratio, two motors total (one for each flywheel). We tested a lot of gear ratios, different number of motors and different motor speeds and even set it to the highest speed, but it would only fly a few feet.

We noticed a lot of teams with 5" wheels and barely any 4" wheels, so after several months, we finally gave in and bought the 5" wheels. There must be a reason so many teams choose 5" wheels, right? :rolleyes:
It now works beautifully. Still with a 7:1 gear ratio, we can shoot full court shots with two turbo motors (one for each) and a motor speed of 90.

Whichever idea you decide to go with, good luck!

I have seen 2 of the teams at our school use 4 inch wheels and they work fine it is just preference. I personally have a 21-1 gear ratio with a speed internal gearing and it is working great(OK it is over shooting which can be fixed in code). This is with 5 inch wheels

Hope this helps

Although 4inch wheels can work, I would personally recommend 5inch wheels as I know a lot of people have had a lot more success with them.

The main differences between 4" and 5" wheels are the fact that the increased circumference of the 5" wheels means a higher angular velocity (circumferenceRPM=angular velocity) and a higher exit velocity (approximately the angular velocity of the flywheel in a perfect system) of the ball at the same RPM, and that the increased mass and radius of the 5" wheels mean a higher moment of inertia (the concept of inertia applied to rotational acceleration rather than linear, calculated with the equation massradius^2=moment of inertia). As a result, the 5" wheels would have a higher spin up time with the same gearing, but can shoot farther and has less variation between consecutive shots. They also require a lower gear ratio for full court shots, eliminating the need for compound gear ratios and reducing friction with the use of turbo motors. I have heard that the rubber on the 5" wheels also tends to behave weirdly at high speeds, but I have never noticed this on a teammate’s flywheel, which can make full field shots at about 79 power, but have seen that they can damage the balls if the balls are too compressed. 4" flywheels can be more compact, especially if they are not designed to score full field shots. As long as you account for the change in angular velocity between wheel sizes, and don’t expect a 7:1 external gear ratio to work with, say, the 2.75" omni wheels, the wheels shouldn’t make too much of a difference.

The team I’m mentoring uses 4" wheels, (2) high speed motors, and the gear assembly is 84T:36T, 84T:12T, the angle is set to ~45*. It can shoot over the high goal without a problem. Reducing friction was the largest help in getting the FW shooter to function well.

45* may be to high of an angle for the sake of consistency.