[FTC]: Linear Slide Thoughts

[robolorenzo]

I am the mentor of a rookie FTC team. I have been around FIRST for a while, but this is my first time as lead (and only mentor). I am not an engineer. After a rookie day hosted in NJ, my students thought of using a linear slide. Any thoughts as to whether or not a linear slide, driven by a single FTC motor, would be able to lift the large ball? I was thinking something along these lines:
https://www.youtube.com/watch?v=mbSP4dkfD2g

Thank you for any help/feedback!

FTC Rookie Team 11180

[GeeTwo]

Assuming you can keep your slide from binding, whether a single motor can lift a given load is a function of power and appropriate gear ratios more than if you have a linear slide or rotating arm or cable winch or whatever. A linear slide is slightly more complicated and heavier, but gives better control. Deciding which mechanism type is optimal is a matter of balancing your strategy, requirements, and capabilities.

Calculate the weight of the load, multiply by the height, and divide by the time you are willing for that load to take to get to that height, and that's the output mechanical power you need (unit converters are available online to get oz-in/sec or whatever to Watts). Make sure your motor(s) can produce 150% or more of this power for that amount of time. If the time is really short (so that the ball is still accelerating noticeably halfway down the track), you'll need more power to account for the kinetic work.

Once you identify the motor, figure out what gear ratio converts the speed that the motor spins into the distance the ball moves.

JVN has a calculator on CD that will do all of this pretty easily at FRC scale; there may be similar calculators for FTC. If you come up with the specifics you're looking for, post your work and we'll check it for you, or post the specific loads and heights and stuff and we'll guide you through the calculations.

[robolorenzo]

Thank you for your feedback!

[RaMoore]

If you're evaluating linear slide options, REV Robotics has one which works with our extrusion building system you might want to look at: http://www.revrobotics.com/15mm-linear-motion-kit/

We also have small pulley bearings for running the lift string: http://www.revrobotics.com/rev-41-1368/

Our extrusion and linear slides are made specifically for FTC teams and are quite a bit cheaper than the 80/20 solution shown in your example video.

As Geetwo said, you need to run the numbers and see if your team can accept the amount of time it takes to lift with the correct gearing, but I think that using a REV HD Hex Motor or AndyMark NeveRest it would probably be fine.

We're also working on a linear slide building guide that will have more detailed examples and it should be available soon. Please feel free to use the "Contact Us" option on the Rev Robotics website anytime; we're happy to provide technical support and guidance.

[pilleya]

Originally Posted by GeeTwo

JVN has a calculator on CD that will do all of this pretty easily at FRC scale; there may be similar calculators for FTC. If you come up with the specifics you're looking for, post your work and we'll check it for you, or post the specific loads and heights and stuff and we'll guide you through the calculations.

If you go to the DATA tab on the JVN calculator you can add different types of motors to it by filling in the different columns in the Motor Specifications Table. The motor that you have filled in the specs for will then become available in the drop-down menu in the other tabs such as the linear motion one.

[Cog]

I'm going to add this as another option for linear slides.

https://www.youtube.com/watch?v=lBVcPxq1KTY

I've worked with the 80/20 extrusion, and in its smaller sizes it can be really finicky. The drawer slides can really outdo the extrusion in a lot of ways, and they've been more reliable for me in the past.