Hello! Welcome back to IntroVex, your robotics guide to Vexcellence.
In our last episode of Build Your Chassis, we talked about the fundamentals of gear ratios and the common ones found in a competition. This time, we will explore ways to create ratios beyond solely relying on gears.
Overall, there are three common ways to create ratios between the input and output while transferring the power from one location to another: Gears, Sprockets, and Pulleys. Later on, we will discuss the PROS and CONS of each and when is best to use them.
Gears
First, let's talk about the gears. Gears in VEX IQ come in different sizes, starting from 12-tooth gears up to 60-tooth gears. All gears are multiples of the 12-tooth gear, including a 24-tooth, 36-tooth, 48-tooth, and 60-tooth gear. Among these, the odd multiples of a 12-tooth gear can line up in a straight line together, while it forms a diagonal slope when one odd multiple connects with an even multiple tooth gear.
When two gears are connected together, they spin in opposite directions. Similarly, when three gears are connected together, the first and the third gear spins in the same direction. Overall, if the number of gears connected is even, the first and last gear spin in opposite directions; vice versa.
Sprockets
Next, let's talk about sprockets. Sprockets are shaped similarly to gears but with the teeth wider apart, and are connected through linked chains instead of connecting them side by side. Sprockets are sized from the smallest 8-tooth sprocket to the largest 40-tooth sprocket. You may also notice, all the sprocket sizes are multiples of the 8-tooth sprocket, including 16-tooth, 24-tooth, 32-tooth, and 40-tooth.
Since sprockets are connected through chains, the motion of all connected sprockets in the same chain spins in the same direction as the input. Also, there is never a limit on how you connect the sprockets. All can be connected as long as the chains can reach both ends while being straight.
Pulleys
Finally, let's introduce pulleys. Pulleys have no teeth like the others, but rather, it is connected through rubber belts just like how it appears in physics textbooks. Additionally, there are only 4 sizes of the pulley: 10mm, 20mm, 30mm, and 40mm (in perimeter).
Similar to sprockets but different from gears, the connection of pulleys requires a belt, which results in all pulleys connected together spinning in the same direction.
Comparison between Gears, Sprockets, and Pulleys
After the brief introductions, let's talk about when you can use the three connection methods as well as their advantages and disadvantages.
Gears:
PROS:
- Powers can transfer flawlessly and directly from the input to the output
- Doesn't have to worry about belts or chains falling off
CONS:
- There are restrictions on possible connections. You might not be able to reach a certain gear ratio with the correct direction of spin with a fixed amount of distance between the input and output.
Sprockets:
PROS:
- Can connect from any location to another
- Can easily switch up the sprockets to reach other ratios
- Can connect multiple outputs to one input easily
CONS:
- Chains may break upon collision or aging
- Need to adjust the length and tension of the chain when connecting
Pulleys:
PROS:
- The sizes are relatively smaller than sprockets and gears
CONS:
- The pulleys may slip easily when rubber belts don't provide enough friction
- Rubber belts are fixed in length, may not find the perfect belt to connect a certain distance
- Cannot connect locations that are too far away
Simply saying, gears are really useful in places where you need precision in the turning, and the power transfer has to be consistent. One prominent example is the chassis. Even though sprockets can also do the job, gears can increase the actual motion transferred to the wheels and avoid the risk of repairing broken chains.
Sprockets, on the other hand, are great when connecting input and outputs that are far apart and not lining up straight. If you tried using gears to connect and found that you cannot possibly reach the destination with the preferred gear ratio and number of gears, it may be best to switch to sprockets and try again.
Pulleys, finally, are uhmm... not really good at anything. First of all, the rubber belts can really slip easily, especially when you want to turn something heavy and requires torque, pulleys may fail the job. One of the better and common usages of the pulleys is using them as side wheels that guide the mechanism or robot smoothly.
Possible Combinations and Applications
After all the explanations, you may think that gears are gears and sprockets are sprockets, which they are, just separate things to consider when constructing. However, this is not always true. Sometimes, you may need two things spinning in different directions, but the distance won't fit an even number of gears with the gear size you prefer. This is the time to combine the two.
Take an example of the side rollers we made in the current VEX V5 Push Back season. The space at the time was 7 holes in between the two rollers, but after simple attempts, we found that we could not find the perfect combination to get a 1:2 gear ratio with an EVEN number of gears. At last, we figured that we could use an even number of gears to power one roller while using sprockets and chains to power another, making the rollers spin in opposite directions.
Aside from this example, there will definitely be more cases, but I am just here to remind you that sometimes thinking outside the box and combining different things can help you find the solution.
