Help Needed: VRC Turning Point Robot

Our robot is in its “final” stages before a competition next week, yet it still has multiple flaws that prevent it from being consistent with its intended purpose. Attached are several photos of our robot from multiple angles; the purpose of the robot, programmed on EasyC, is to be able to flip over a cap to the alliance’s color using its prongs (which will eventually fold up to stay within length limits), and then be able to lift up the cap and potentially place it on a pole. The following bullet points are regular flaws with the robot and our team’s attempts to fix them:

1.) The chains on which the prongs are attached to have a tendency to unsnap links at random times, specifically links near where the prongs are attached. We feel this is very likely to be a result of the attachment (screws inserted through the prongs into the links) putting too much strain and pressure on the links, and after multiple uses it eventually snaps. This is one of the biggest issues we are having with our robot, as we cannot think of a better way to attach the prongs sturdily to the chain while minimizing strain and still be able to get the chain over the sprockets.

2.) When the prongs try to lift the cap, it has a tendency, when the cap is absolutely covering the prongs, to bend downwards and cause the cap to slip out. It is difficult at time to get the cap completely situated, especially when timed, so we tried to alleviate this by attaching upside-down screws as “spikes” onto the prongs to catch onto the underside of the robot, but this instead led to the next problem.

3.) If the cap does get lifted, it is usually difficult to get it to slide off of the prongs and onto the ground or a pole. We believe the “spikes” are catching onto the cap too well and preventing it from sliding off without having to shake the robot repeatedly. Yet, if the spikes are removed, the cap aforementioned tends to slip off the prongs, thus creating a cycle our team has yet to fix. In addition, if the cap slides off the prongs, it has a tendency to flip in the process, thereby resetting our progress towards scoring points. We have also recently tried rubber bands to keep the prongs level (not pictured), but these catch onto the prongs and create snags, as well as not really being a major help in preventing the prongs from bending.

4.) The robot is relatively unreliable when it comes to flipping the caps. Our strategy is to try and slide only about half of the prongs underneath the cap and lift, so that the cap gets knocked off balance and flips over to our alliance’s color. Yet, it is rare that this actually happens, as the cap usually just rocks for a few moments before staying still and unflipped. Trying to use more of the prongs either accidentally lifts the cap or gets it caught on a “spike.”

As shown, we sadly need a LOT of help before this robot can compete well next week. Our main questions, then, are what alternatives can we use to get the cap to stay on the prongs besides the counterintuitive “spikes,” how can we lower strain on the chains to prevent snapping, how can we consistently flip a cap and lift a cap (preferably keeping the two processes distinct to prevent accidental crossover), and how we can prevent the prongs from bending down while lifting. Any and all help would be appreciated in trying to fix our robot, and while we are constrained on time, we would also take any suggestions on majorly redesigning our robot to better flip and lift caps (we have a secondary robot to shoot balls and take care of the flags). Thank you all very much!

Have you considered zip ties in place of the chain screws? They’ll flex more, hopefully leading to lesser chain breaks.

For the “spikes,” have you tried shorter screws? If so, what about antislip on the prongs themselves. Rubber bands would do the same thing, if used correctly.
Additionally, I could envision cut off zip ties being used as “spikes” possibly. They might provide just the right amount of resistance, if angled correctly.

As far as dropping the cap into a pole, does dropping the lift and driving away not work? On the ground, doing a hard stop to get the cap off might just be okay.

Not sure how many resources you have at your disposal but if you get access to a linear slide, it is much more sturdy and can likely hold the weight of the cap and claw without bending downwards like this chain tends to do. It also appears to be a-symmetrical which is not good, you also have screws in the sticking out the claw which prevents the cap from sliding however a friction based solution is probably more viable. Try friction mat instead. Also, zip ties are not meant for holding functional parts of the robot in place, they are more for wiring and things of that nature because they flex and bend easily.

So to decrease the slop I would put something on the prongs that latch onto the C-channel. Most linear lifts use slides for this reason. I can post pictures of this if you’d like me to. Now I personally would recommend a 4-bar design instead of a linear lift for this purpose. They’re easy to build and very effective for this purpose. You can also find many videos on YouTube instructing you on how to build these.

I just pitched an idea, if you’re referring to me. I’ve seen some very strong zip ties, and their flexible tendency might just be useful in this application. (I’ve actually never built a cascade lift like this with chain, so… I’m no expert)

If you’re referring to the OP’s pictures, I think it’s probably okay, given their time table. Although I would personally feel more comfortable with 1/8" braided nylon rope.

As a builder stressed for time myself at points, there might not be time for an elaborate redesign. Although I would totally look into it after the upcoming comp.

As for slides, they might just be better than whatever is going on there. But the OP probably doesn’t have time or access to these to install, hence asking for elaborate help here.

Okay, I’m starting to ramble. I’ll shut up for a bit.

I agree that a redesign may not be an option, I was offering a suggestion for future competitions if they have any, now I am not saying that they add slides, but just a small piece that holds the prongs to the back of some smooth area and slides up and down with the claw.

can that even reach the posts?

Given the current general design and time frame, I’d consider trying to put arms in the place of the chain elevator. Pop off the chain, screw a long c channel onto each of the gears (so that when the gear turns so does the c channel) and then attach the prong piece stationary to the other end. Then you should be able to at least flip caps consistently with the tips.


As others have said, a linear slide or cascade lift setup is often used to accomplish what you are trying.

Using more industrial-style zip ties in place of the chain screws could work, but our only concern is the chain still snapping from the pressure exerted by the ties. Would those still be able to keep the (somewhat heavy) prongs level?

The antislip material and rubber bands ideas sound great, we will replace the “spikes” with either (or both) of those and see how it fairs; if it still needs something more, we will try the cut zip ties idea.

Sometimes the cap gets caught on the “spikes” when dropping onto a pole, but with them out of the way, the robot should be more effective in doing this. The hard stop doesn’t always get the cap off, but the removal of the “spikes” should alleviate this.

We would love to replace our current design with a slide system (our design prior to this ironically was to do a slide elevator system). The only problem was that we did not have enough linear slide track to make a tall enough elevator, and as such we had to resort to this design due to time constraints. If we can somehow get the order before next week, we can try and replace the chain gearing with a slide system. Any suggested designs for building the scaffolding the system would be attached to?

It probably wouldn’t take a long time to disassemble or take off this lift and change it to a 4 bar or 6 bar which might be a little bit sturdier.