Our team would benefit from seeing images of applications of this technique on FRC elevators.
Thanks in advance!
I recommend looking at 1619’s elevator from last year to see an example of continuous rigging with constant force springs. Their reveal video can be found here. That is the only one I can mentally remeber right now.
Here is a picture of 1923’s robot from last year where you can see the two constant force springs behind the elevator. The springs were mounted on delrin rollers that were constrained on the same axle as the top pulley for our belt driven elevator. The springs are stretched down and bolted to the bottom of the 1st stage of the elevator. It’s not the clearest picture, but it is a fairly clear example of a really simple way to implement cf springs.
3 Likes
Team 3991 used constant force springs but they did not work as well as we would have like because our intake was too heavy so we used surgical tubing instead.
So, would the idea behind using one of these to be to use JUST enough to make the elevator lighter to lift, but enough that gravity can keep it down / in place and it not snap up without motor current? I’ve never done one of these designs before.
I believe the goal is to use a spring that has just enough force to cancel or almost cancel out the force of gravity on the elevator system so there is less torque required to lift the elevator and thus it can be done faster. This also would result in less torque to hold the elevator in a certain position as there is theoretically no force pulling the elevator down. The elevators up and down movement is based on the pulley run which will generally have a cord to pull the elevator down. By requiring less torque, one can use smaller and faster motors with a lighter gearing to save weight and create a faster system.
Ah, so you’d have a run of pulley to pull the elevator up and another to pull it down? Theoretically attached to the same spool?
Yeah. Look up how cascading and continuous elevators work. There is generally one spool which is wound so that as one side lets out, the other pulls in at the same rate and vice versa. This means your carriage will not bounce as it is being held from both sides. So if you stopped the elevator suddenly, the carriage won’t fly out the top. We used gravity to pull down an elevator a few years ago and regretted it as it was significantly slower than if we pulled down the carriage
I can get you some pictures our robot from last year which used constant springs on the elevator. What parts are you most interested in?
1 Like
Vulcan Spring provides up to 6 free constant force springs per team, in your choice of lengths and forces (1/4 to 41 lbs.).
Uploading: 20190116_135148.jpg… Uploading: 20190116_135154.jpg… here’s some pictures up close
I couldn’t open your pictures.
Is it common/effective to do a separate spring for each stage?
My bad here they are https://imgur.com/a/L5S7ilk. Yeah we used 2 springs for the first and just one for the second cause the first stage has to lift the second. Those plates at the top made it super easy to take the springs off. They allow the spring to be fully relaxed at the max travel so they don’t shoot off when they’re unscrewed.
I’d be careful when using these - I’ve heard horror stories of them cutting or crushing fingers and plenty of people too afraid to use them
Thanks. I’m curious: in the last image is the piston and red mechanism a method to hold place after climbing?
Yes - I’m wary as I’ve heard some of that as well.
As long as you use vice grips and try to limit human contact as much as possible (and unlike power tools do use gloves) you should be fine.
Still, we did just fine last year with an elevator with nothing whatsoever to counterbalance it, so I would argue that maybe the safer solution is also worth considering.
The red mech is a ratchet on a single acting cylinder so we don’t have to rely on the motors to prevent backdrive. It might’ve helped with climbing but we never tried it. It’s a 3d printed part made of petg
Hmmm… do you have an example of how to do a counter balance? I’ve never seen that solution.
No because we just used motors
Most people counterbalance with springs