FTC Rover Ruckus Latching Elevator Issues

Technical Technical Discussion
1

I am a part of FTC 6962. Our team is from Hawaii. Nice to find a forum for FIRST! Glad to meet you all and aloha! (We really don’t say that often, lol)

Anyway, we recently redesigned our robot. Now it has an aluminum water jet cut frame. It turns out that our new robot weighs 25 lbs with the battery and the phone.

The elevator works by attaching a C-channel to a chain that is driven by a motor. 2 idler sprockets are at the top and bottom of the C-channel holding the moving C-channel. The chain is driven by a 60:1 Andymark Neverest motor directly using a 24 tooth sprocket.

Now I thought that the robot is fully assembled, I tried to test the elevator to climb. It turns out that the elevator is not strong enough. It pulls the rear wheels off the ground and stops. I am thinking the torque of the motor should be strong enough, as it calculates to about 34lbs/in for the 60:1. I am a bit stumped. I thought that the elevator would work.

Anyway, should we replace the sprocket on the motor for a bigger one, or is there another thought someone had?

2

We have the same lift mechanism, albeit powered by a wormgear. We used that so we don’t backdrive before the match starts. I would highly recommend the same.

Here’s a link to a practice match of our bot in action:

3

This is one of the thoughts we had, but our team has no access to a worm gear. Our school (Punahou School) has like 8 FTC teams and due to this, all 3 of the worm gears that were available are being used by other teams.

Would you suggest anything else?

4

Is there any way you can order one? We use this wormgear and use a 10:1 powered by a 40:1 motor.
https://www.pitsco.com/Competitions-Clubs-and-Programs/FIRST-Tech-Challenge/Robotics-Elements/Motion-Elements/TETRIX-Worm-Gear-Box

If not then You should try to gear it down more. Battery will go down over the match, and you’ll need a way to keep it above 4" starting in Auto.

5

Yes, I am thinking I need to gear it down more. Sadly, our regional tournament is this Saturday. Which puts us in an interesting situation. As my dad and our team coach says,

“Well of course it doesn’t work, everything else is working fine!”

:yikes: Only a few days to get this working! Urgh… Thats a lot of late nights.

6

I’m not quite picturing your setup, but normally, putting a bigger sprocket on the motor would increase the speed and decrease the force applied to the chain. As such, a smaller sprocket on the motor is in order.

Also, check the chain and other systems for binding. A bit of filing, alignment, and lubrication may get you over the threshold.

7

Options-
smaller sprocket could work.

  • minimize friction everywhere in your system.
  • add a spring or rubber tubing to assist with the lift.
  • add another motor.
8

Would gearing down the motor is an option? It seems very viable in my opinion.

9

Hmm, that is very good advice. I am thinking that gearing down the motor could work. Could that fix our issue?

10

Gearing down is an option, without a picture it’s difficult to advise on viability. Smaller sprocket is equivalent to gearing down to a certain degree.

11

Yes, lower gearing (that is a ratio of 80:1 rather than 60:1) would help. Going to 40:1 would be the wrong direction.

To find out how much more force/gearing you need, you could put the robot on a scale, and see how much the robot still “weighs” while trying to climb. Note that gearing down by reducing the sprocket size will mean re-tensioning the chain; not sure how you’re doing this now. If the chain driven by the motor is more than about 30 full links long, you could likely go to a 20 tooth sprocket and remove one full link from the chain and have it all work out in the same position. This will get you about 3 more pounds of lift. Going to a 16 tooth sprocket and removing two full links will get you about 8 pounds.