Refining our DR4B

What do you mean warping? Are they literally bending? Can you post a picture?

I could be wrong, but it appears you have your gears rotating around shafts. The problem with shafts is they are not very sturdy and can wobble around a lot even through bearings, which could be why it looks like your gears are bending slightly. Instead of using shafts, use a screw that is locked to the mid-section with a keps nut, and plastic inserts for your gears. If your mid-section is 6+ holes wide (which it appears to be), you will find that Vex doesn’t make screws long enough to go through both structural bars. Use a nylock and a teflon washer to keep the gear in place, leaving some length of screw sticking out. Don’t tighten the nylock too much or you will create unnecessary friction. Use a standoff to connect the remaining length of the screw to the other side of the mid-section so that it won’t be able to bend. That should eliminate any problems you experience with the gears.

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Here are some pictures:
They don’t show it that well but the actual gears themselves are bending which is a slight problem.

Huh that actually sounds pretty good. Yeah our spacing is 7 holes so a normal screw won’t go all the way through. I think we should be able to make the spacing one less but I’m not sure if it’s worth it?

Make sure your spacing is as tight as possible without making metal rub against metal. Also I see that there is a small amount of space between your gears and the lifting bars as opposed to having the lifting bars resting right against the gear. Get the gear as close as you can to the lifting bars for a little extra support.

Surprisingly your shafts have not bent yet, but with a length like that you would definitely experience this in the future. Last year in TP we managed to get fit two lifting bars with gears in a 4 hole wide space and still had problems with shafts bending. You could either replace the shafts with HS shafts to prevent this even further, or do something like 1814D did in TP with their cap bot.


The reason we put the bars a little away from the gears is so that we would have spacing for rubber bands on both sides of the bar and so that if the DR4B flexes a little bit when going up or down the 4 bars won’t interfere with each other. We’ll see if putting them flush with the gear will work though.

I think I’m gonna change the axles on the driven gears to screws but any advice on the drive gear? The only thing that it seems we can do it switch to high strength axles if we don’t want the axles to bend.

I would recommend doing what Technik3k showed in the thread about partially threaded screws. We tried this design and it worked very well. If I remember correctly it was about 5.5 holes wide so you only needed one screw. As for the drive gear, you can sandwich it like Technik3k did as well, and you shouldn’t have to worry about it bending. I would recommend doing this whole setup wit 84 tooth gears however, since you will be lifting large loads in this game.


Hm I think it’ll be kinda weird with a wider mid-section but with the standoff/screw method I think I can make it work.

Should I also change the top 4 bar to half c-channels to make it lighter? I’m just worried about the half c-channels bending at the top. I’ve also heard that the half 3 hole wide c-channels would be better for this because it’s a little stronger than half of the normal 2 hole wide c-channels so I’m debating switching to that as well.

If you’re using aluminum, then it’s really not that much weight for just a four bar. If you are using a 6 or 8 bar for your top linkage, you might want to consider it. We used an 8 bar for our top linkage and it works fine without the cut c-channels. It really depends on the weight of your intake and how many cubes you intend to hold at once. As for the half c-channels bending, I haven’t heard of that happening. Many teams used them ITZ and they worked fine. While it does seem that using half c-channels would decrease the lift’s structural integrity, I have seen no evidence to prove it. I don’t think it makes that much of a difference though so it’s not worth switching to them if you didn’t start using them.

It might just be the angle, but it looks like the two towers at not the same distance apart at the bottom and top. This would make it less stable, and it would cause the gap between the gear and spacer in the second picture to occur. Hope this helps!

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Uh that would suck if it’s actually different because both towers are spaced the same. I hope the c-channels aren’t bending.

I’ve seen people use two high strength gears bolted together on their DR4Bs (for a total of 8 high strength gears) and was wondering if that is worth the extra weight it adds? Or would using screws and reducing the spacing in the midsection do essentially the same thing?

This would do basically the same thing. Most of the teams that do that use axles, so having two gears would allow for less wobble. This isn’t really a problem if you use screw joints. Also, just in case, you might want to brace the two parts of the tower together.

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Ah okay.

Right now we have a c-channel across the entire midsection keeping it together, a cross-brace across the middle towers to keep the DR4B moving as one unit, and standoffs connecting the bottom of the towers, but not going across the entire mechanism.

I mean the two half c channels that have the gears between them should be attached (a standoff or c channel should work). Sorry if I was a bit confusing.

Oh whoops I think I replied kinda awkwardly. We do have a standoff going between them and a c-channel across them but only at the very top and bottom.

Ok. That should probably be enough. It was most likely just the spacing then.

There’s a 99.5% chance that the bars are angled because of the square holes. Take a tape measure to check the distance between each bar all the way up each half of the midsection and if there is a difference between the top an the bottom, loosen all the screws connecting them slightly, realign them, and get a friend to hold them while you tighten the screws again. This is probably just another vex square holes ftw situation.


Okay first off I just want to say thanks for the screw+standoff idea and using the kep nut to keep the screw straight because those really helped lessen the slop in our DR4B. Now the only problem we have is our 4 bars are too close to each other so now they hit each other when we go up and down. We’re hoping that putting a brace across the bottom 4 bar will help with that though.

Do you mean the two linkages on each half of the lift are hitting each other or the two halves of the lift are hitting each other?

Um I think I mean the two linkages on each half of the lift are hitting each other. I can send a picture of it to make sure we’re talking about the same thing?

Also since they’re too close I can’t put rubber bands on both sides of the lift arms rip.

I think a picture would be very helpful.