I wasn’t sure where to post this, so I just put it here. Our team is building a double reverse 4 bar for the competition and have been having some trouble with the transition from the first to the second stage. At first, we used gears but they kept slipping and popping from the weight. We have been looking into Pastoral Invasions’s 4252A reverse double 4 bar with the bar transition. We were wondering how this worked, as we found the picture, but were unable to determine from the it how the bar was connected.
Can you please include a picture with a highlight of where you are experiencing the issue?
Gear popping can be reduced when the drive gear is braced with other gears to help hold it tight. Depending upon how far away the top and bottom gears are from each other makes for a long drive train meaning you have to have both top and bottom with extra gears to sandwich them in place.
Last year 80Y had the top and bottom drive connected together on their double reverse four bar. But this year you need more height so that may be spread about.
Are you using bearing flats for your gearing? Try using some if you are not doing so. Also try to make your shafts as short as possible. Short shafts are proven to reduce gear popping. Check out 7682’s youtube channel.
Also, try to design things out prior to building. That helps a lot.
Before, we used the bearing flats with the gears right next to brackets bracing them together, we are using two high strength gears in series but they still kept popping. I will include a picture soon.
What you are referring to (and linked) is actually one of my old robots. That bar linkage was developed because I was unsatisfied with the slop that gear driven rd4b’s had. The whole idea was thrown out at the time because sack attack didn’t even require height.
However, I have looked into the bar linkage again, and have made some changes.
The gist of how it works is that as the lower part of the rd4b raises, it pulls the linkage downward, which pulls the opposite side of the upper section downward, allowing the top section to raise up. Here’s a short video:
With this setup, it’s slightly important to realize that the trajectory is not a perfect linear up and down, but rather a slight “s” curve. It is also hard to start lifting, as the starting angle between the linkage and the top bar is small. Rubber bands can help that, though.
I have a rd4b lift that had the same problem. Shorter shafts and using bearing blocks helps. I ended up running a ziptie to the top and bottom shafts right close to the gear. Its not the best way of doing it, but it did stop the gears from skipping and the lift works great now.
The Pastoral invasion RD4B post doesn’t look like its much to work off. (Was it even finished? )
A linkage idea seems like a potentially good idea. However using string rather than metal/standoffs may be better so you can tweak the linkage length, it didn’t look like some of those linkages would give perfectly linear motion…
That’s transferring a lot of force through pieces connected at right angles. I see it bending.
Why not just use the “no gear” methods that already exist? They’re simpler.
I have built and tried the new design and have had some success. I added the reinforcement to the gears and rubber bands to hold the first and second stage. For the “no gear solution” I have used a piece of paracord attached to the front of the seconds stage to the middle part of the first stage. I have yet to mount the arm, but so far, the design looks very solid. I will update as soon as possible.
We have finished building the arm and it looks great! The rubber bands and metal reinforces stop gear clicking. If this can hold up, with the added weight of the cube and skyrise section, I won’t have to employ the “no gears solution” but the option is always open… :rolleyes:
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