FRC Blog

Spring Tweaks

Mar 02, 2017 Written by Frank Merrick.

 

During the New Hampshire Week Zero event we saw more damage to the springs (‘pegs’ in the manual and drawings) and spring points on the gear lifts than we had expected based on our testing. Springs were getting bent such that they did not return to their original shape and points were being broken. But we have some things we’re doing  to improve this situation.

 

Most immediately, we are providing events with extra replacements. 

 

We are also switching to a new point design. You can see the new design here. The new point design uses slightly thinner material than the original (0.19 inches versus 0.25 inches), but otherwise the point has same shape, at least on the portion that extends from the spring. Also, it is made of LDPE instead of ABS, and is more likely than the prior design to bend rather than break during gear loading. At events, you may see a mix of both types of points in use. The LDPE material does have some tendency to move back to its original shape when bent, but during matches pilots in airships can use their hands (assuming they don’t reach outside the airship) to help the material return to the original shape if they feel a point is bent to an extent that will interfere with gear transfer.

 

Also, we are investigating ways to reduce damage to the springs themselves, through a change to mounting. This change is not likely to be ready for this weekend, though we continue to work on it.

 

With all these changes, we are attempting to retain the form and basic behavior of the original design as much as possible, while at the same time making them more robust.

Field personnel will be keeping watch for damage to these elements during events, as they do all other elements on the field, but if you see a spring or spring point that looks like it needs attention, please point it out to a volunteer working the field.

We will be formally incorporating any design changes we make in future Team Updates, but we wanted to give you a heads up about these in advance, as you will see some changes at events this weekend. We’ll also be doing a supplemental email blast to all teams about this.

Thanks for your patience as we determine the best way to solve these issues!

Frank

Comments

The event that we encountered with our practice peg (printed from ABS) occurs when the gear in the robot aligns so that the peg hits a solid part of the gear. If the contact point is not too close to a gear opening, the flat end of the peg does not allow it to roll or slide to one side or the other. LDPE and a thinner peg will be more robust but a spherical tip on the peg would likely allow it to slide to the side more easily when this type of encounter occurs. These 'head-on' events were more common than we expected.

Team 2165

I just wanted to say thank you for all your hard work.  I know a lot of different people put in countless hours to get ready for these events.  I have only been a coach for 2 years with team 4632 out of Monticello but I am HOOKED!!  The events in MN are top notch and each and every volunteer at the North Star event held week 6 at Mariucci Arena in Minneapolis does a wonderful job.  All of FIRST and the volunteers that help out our teams are AWESOME!!  Thanks again for looking into the Gear Points on the lift station.  I appreciate your efforts:)

Thanks for the heads up, Frank!

Hi, Sorry to hear of the issue. I am concerned that the new design seems to require the spring pass through the gear by 1.5" to catch the gear due to the slope on the front. We do not that much space behind the gear's holder.

Suggest using polycarbonate (polycarb) plastic for the spring point as it is very strong, can be bent and will return to its original shape.

When you issue field drawings, please include critical dimensions in feet and inches for things like the height if the spring above the floor, the distance from the spaceship face to the center of the rope, etc. The forum has dictated that these dimensions should be figured out using the field construction drawings. These field drawings are shop drawings to be used for constructing the final field components. After much drawing searching, I have trigged out that the rope is approximately 22 inches from the face of the spaceship. This should have been a given dimension. This is a continuing problem. Every year, shop drawings are usually the only source of critical field dimensions

This is an issue in the Lake Superior Regional competition in Duluth MN. this weekend.  I attended yesterdays (Thursday) practice matches and observed at least one broken tip and two springs that were bent.  Each equipment failure cost teams valuable points during matches.  These equipment failures are a great disservice to the competitors.  They determined winners and looser in several matches.   The teams put a tremendous amount of time and effort into design and building their robots.  FIRST should do the same.  

Have you explored using a thick walled rubber tubing instead of a spring?  Something that would retain its shape, yet provide some shock absorption on robot impact.
 

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