We are a 2nd year team and are looking to make an intake to grab balls. It seems from looking at pictures that many teams use the versaplanetary gearboxes for their intake systems; however, it is unclear what type of ratio is used in the gearbox.
Can someone give us an idea of the gear ratio they are using for their intake? Also, if someone is using something other than the versaplanetary we are open to that as well.
Lastly, do you use the bag motors or the 775 motor for your intakes? Thank you
We used an intake for grabbing cubes last year. It had 10:1 VersaPlanetary gearboxes powered by a single 775 Redline, each of which was direct driving a green compliant wheel and belt driving another compliant wheel. It worked very well, and I’d recommend something similar as a starting point.
The intake speed and torque are ultimately determined by both your gear ratio and the size of the wheel / roller used to pick up the balls.
You want more than enough torque to move the balls through your intake, which is hard to predict as it depends on your particular design.
Many teams start with an intake set that so the intake wheels go 1x-2x the speed of the robot (in feet per second, not RPM), to allow them to more easily pick up balls that are moving away from them. That kind of speed may not be as necessary this year due to most of the balls being kept in restrained corners.
The best thing you can do here is to prototype. The VersaPlanetary is a very easy gearbox to change ratios on, so buy a couple of different options for a 2 stage VP and see what works. For a 2" wheel I’d consider something like buying sets of 3:1, 4:1, and 5:1 gear reductions and swapping pairs of them in and out until you get performance you like.
This is all assuming you’re using something like a BAG or 775 for your intake. If you use a CIM you’ll need less reduction (but will also have a heavier intake).
First, full disclosure: I used to work for AndyMark.
Before the gear ratio, you want to figure out how fast your drivetrain is going. Your intake roller should have an appreciably higher speed than that, so you don’t run the risk of running over the game piece you really would rather intake. AndyMark claims 10 feet per second for a stock AM14U4, so we’ll use that for this exercise. Some people like to double it, but I’m going to go for 15 ft/sec for this.
Let’s say you’re using a 2" wheel, which has a circumference of 6.28". To get 15 ft/sec 6.28" at a time, you need about 29 revolutions per second or about 1700 RPM.
The AndyMark Redline A motor that came in your kit has a free speed of 21,000 RPM. Using a 12:1 57 Sport gearbox (or a VersaPlanetary, if that’s your jam) gets you 1750 RPM. Close enough.
By playing with the wheel diameter and sprocket or pulley sizes, you can achieve a comparable speed from other ratios as well. Hope this helps!
Edit to add: Also, make sure you’ve got something to your design so the motor won’t get stalled out. RedLine and 775pro motors die very quickly in that situation, so some combination of letting the roller slip once you have a ball, current limiting in a motor controller, or driver gentleness (the least reliable) will help you prolong its life.
An awesome resource worth mentioning is JVN’s Mechanical Design Calculator. This spreadsheet allows you to play with any combination of motors and gear ratios as well as mechanism type to design a mechanical system to fit your needs. This video provides a walkthrough of the JVN Calculator.
You have to calculate the gearing based on your design. As Chris_is_me said, the linear speed of the edge of your wheel/roller should have linear speed 1.25-2x faster than your robot so it can pick up while moving forward. I’d recommend watching this video https://youtu.be/U4pgviiEwLg among others. It’s in the context of calculating torque for an arm, but the ideas apply also to a pickup. Then use JVN’s calculator for your application.
The specific hardware you use to spin “something” to collect balls, probably depends on how you plan to collect them. We’re going to try a wide, horizontal roller above the ball this year, and that means that it’s kind of difficult to drive this thing directly from the output of a gearbox. We plan to add a small chain so we can place the motor/gearbox next to the roller, rather than sticking out the end of it. The chain will also give us more speed reduction, if desired.
I highly recommend the JVN mechanical calculator as well. I have seen very good success with a 12:1 and a 775 pro. The JVN calculator will be able to help you adjust for what your specific system is.
We are having issues with our intake. We are using 775pro motors with a 10:1 gearbox. We have tested 2 balls and have cut them both. We are not intaking from the ground, just from the human station so we are not moving when we collect the balls. Any tips would be greatly appreciated.
Note: The above issue also has its own topic: