DR4B Tutorial by 333A

[333A]

It is that time of the season when beginner teams are searching for resources to assist them with building their first DR4B lift, and senior teams are looking for new ways to build taller, stronger, and more stable DR4Bs, improving on their designs from past seasons.

Hence, we decided to make this DR4B Tutorial by 333A.

• In our guide, you will learn how Double Reverse Four Bar (DR4B) works.
• New teams will find step-by-step instructions how to build a good DR4B.
• It explains the main factors of stable DR4B: Screw Joints and Cross Bracing.
• This guide shares building tricks we’ve acquired and the lessons we’ve learned.
• Other references are linked for teams to research and improve upon our design.

Finally, we are working on a video counterpart for this guide, which will be found here upon its completion.

Some highlights of the DR4B/8B that we built at the beginning of the Tower Takeover season:

These are bearing extensions on the rotating bars of the lift. They extend as far as possible while still allowing the screws to go through both sides of the midsection. This minimizes wobble as much as possible:

These are some of the bracing techniques we used, namely X Bracing and K Bracing. They both use triangles to reinforce the lift, since triangles are the only rigid 2D shape. This prevents a lot of torsion that would otherwise become a problem:

This is the rubber band triangle on the bottom linkage of the lift. Using a triangle formation allows the lift to raise with uniform acceleration, which allows for more consistency in a competition. We but them around loose spacers to allow the rubber bands to rotate without the risk of snapping:

Conclusion:

DR4Bs are very useful lifts for VEX Robotics. In addition to being extremely tall, they rise linearly, making them useful for almost any challenge involving lifting objects. It’s clear why they dominated in past games such as In The Zone and Skyrise. However, in order to be competitive, they need to be built with maximum stability.

The most important takeaway from our research was that you should use screw joints whenever possible. This change had the greatest impact on the stability of our lift, and forever changed the way we build anything.

Bracing is also very important, and can’t be overlooked. There are many effective ways of bracing, and all of which have their respective benefits.

Lastly, we learned to not fear the unknown. Had we not tried new things, our lift would still be a twisted wreck that lifted at an angle. Learning more about DR4Bs has not only improved our lifts, but all other aspects of our building.

Remember that there are many great methods for building DR4Bs, not just the one presented in our document. Each one has its own merits, and learning about new methods will help improve your own.

Good luck with your future endeavors!

References

1. Team 5225A - The Pilons (check out their ITZ season DR4B CADs)
2. Kepler Electronics Video (great explanations, but axle shaft joints may wobble)
3. Comparison of VEX joints (spoiler alert: @Owen thinks screw joints are the best)
4. @technik3k mini-tutorial (on how to build rigid DR4B lift using 2" long screw joints)

Recent DR4B discussion topics:

• Dr4b issues
• Cross bracing
• Refining our DR4B

[333A]

DR4B tips from ITZ world champions Team 5225A:

@nickmertin

Here is an album of pics of our worlds ITZ robot, many of which show the DR4B. I’d recommend you take a look at the methods of attaching elastics, how we braced it, and the different ways of saving weight (depending on how you’re planning on using it). A major factor in our design was the thinking that we’re only using it to lift one cone at a time, which is fairly light, so we don’t want 5lbs of overhead; this thinking may or may not carry over to the current season, depending on what you’re thinking of for design.

Excerpts from: Tips for Stabilizing a Lift (Prevent Sway)

@400X

Obviously, you want to figure out where in the lift the instability is coming from and reinforce or tighten up that part of the system. … Instead of looking at the whole lift for instability, analyze it one section at a time.

There are a lot of ways to “stabilize” a lift, one way you can remove a lot of the slop is by using Single-Rotation Joints . That’s a video on common joint designs in VEX from Owen of BNS. I’ve linked to the last part of the video. In case anything was unclear, you’ll want to firmly attach a Screw to one of the bars with a tightened Keps nut. This will remove a lot of the slop and keep the screw perpendicular to the bar. Then you would run it through a bearing on the other bar so it can rotate, and then hold it all together with a Nylon Lock nut, just tight enough to keep it from coming apart. This joint only rotates in one place and you don’t have to compromise between a tight lock nut to remove slop and a loose lock nut to prevent friction. I would highly suggest using these wherever you have a joint using screws.

You will definitely want to run some cross supports between the two sides of your lift to prevent it from swaying side-to-side. Make sure the spacing is correct so you aren’t pulling them together or pushing them apart and adding friction. You want the bars to always be parallel between the left side and the right side. This isn’t referring to your actual linkage, there are some instances where the bars within the linkage could be non-parallel. I mean when you look top-down at the robot, not from the side.

Not as many teams do this, but I always like to sync up the two gearboxes when I build a lift. This would mean running a shaft that goes through the left gear train and the right gear train to forcibly keep them in sync. This helps a lot with tilting side-to-side. Its best to have that shaft on as small a gear as possible because x Degrees rotation on the smaller gear will equate to less vertical movement in the lift versus the bigger gear. …

I would highly suggest studying 118’s Skyrise reveal very intensely. A lot of teams have made great DR4B’s and DR6B’s, but 118 was one of the pioneers of this design. The Double-Reverse lifts had extremely limited use before Skyrise and 118 had an insanely fast and stable lift from the very first competition that year. Other teams may disagree, but as a South Texas competitor, I always see 118’s DR4B as the beginning of the era. They didn’t invent the design, but theirs was miles ahead of any other I’d ever seen before. A very important thing to note was how they used C-Channel Extenders to increase the stability of their joints and reduce torsion on the bars within their lift. Freeze frame here at 1:09 and look right above the 84-tooth gear on the left. They’ve put a C-Channel Extender inside the main C-channel and run the joint all the way through. 2587z was another brutal Double Reverse Lift that year as well as AURA in VEXU.

That’s all the specific tips I have at the moment. Keep in mind the different ways the lift can be unstable, and I’m sure you’ll be able to invent your own solutions as well. It can sway sideways, the lift can tilt sideways (One side is higher than the other), and then these could both happen forward and backwards as well.

Keep your joints tight and your COG centered, and I think your DR6B will be very successful.

@Owen

Just to add to that response, the best type of cross bracing between the bars in my experience looks like an X. This can keep the lift from flexing more than just a bar across, since it reinforces the lift in the direction that the metal is strong in. (it would need to lengthen or shorten to flex much with X bracing)

@Connor

…
The main reason why my robot worked so well with one motor with 200 RPM and 1:7 gear ratio is because the lift, although looked bulky, was incredibly light (Seen in the reveal, they are using C-Channel Box bracing rather than X-Bracing, because it’s lighter and smaller) and the banding was tuned explicitly to be near linear with only two points. So, if you want your lift to be fast and only use one motor you need the following:

• Light field elements and in low numbers
• Lift that uses KEPS screw joints, in all places possible (Even through the gears)
• Lift has no more than 2 axles for its support, so you can track the position of the lift with a potentiometer

…

If you lift up 10 of the cubes, you will be lifting up roughly the weight of TWO mobile goals, or 1 Mobile goal and 10-12 cones if you know the struggles from In The Zone. My cap bot only lifted 0.6 Ibs of weight. So if you’re planning on doing one motor you should be either doing 100 RPM 1:7 with one motor or 200 RPM 1:7 with two motors, and even that will likely be more or less a struggle for most teams.
…
Delta IV Iteration 3 Close Up: Delta IV Iteration 3 Close Up - YouTube

@technik3k mini-tutorial about building very stable DR4B with 2" long screw joints:

@technik3k

It is a well known “secret” among the veteran VRC teams that it is best to use single bearing screw joints when building 4B, 6B or DR4B/6B lifts. With them you can achieve minimum slop, which translates into more stable lift that could go higher with more precision and less wobble.

To reduce slop and increase precision further you can use longer (2") screws, They act both as a gear axles and rigidly connect sides of the DR4B mid-section.

…

@technik3k

@Anomalocaris, that is a good observation about the top gear being offset forward - there are multiple reasons for that. As @AperatureLabs correctly pointed out, the main reason for the offset gear was to move top bars forward such that their top/forward joints could be fully in front of the tower.

Also, splitting mid-section in two, allows precisely adjustment of distance between the gears (@Got_a_Screw_Loose got it right), improves its structural rigidness, and makes it easier to build entire DR4B in two separate pieces and then assemble them together.

The focus of the original DR4B post was to show how long screws in the joints could improve stability and precision of the DR4B lift.
…

Even more DR4B building tips:

@CSpencer

Here is my ITZ robot which was a cross between a dr4b and a 6-bar.

My tips for you are that you need to keep everything consistent, both sides need to be cross-braced or connected together in some way or form. This year if you are expecting to lift more than a few cubes you will need 2 100RPM motors and probably a 1:7 ratio. I would personally power the lift from the middle section much like the ITZ robot I linked you instead of powering it at the bottom like the other video.

If you have high strength shafts I would use them especially this year because of the weight being carried by the lifts, just be sure not to rely on them and instead rely on x-bracing.

@Jarred

A few simple mechanical things that might be the issue:

• Make sure the rubber bands on each side are equal
• Make sure the pivot points are the same (correct) tightness
• Make sure there is not binding or extra friction in the gearing or pivot points
• Slightly pull the axles from the motors and move the lift by hand to try to find specific bad spots
• Make sure you’re using all the same gearing in your motors
• Make sure everything is symmetrically balanced.
• Make sure your entire lift is square (the arms are 100% parallel)

@Team80_Giraffes

Cantelevering is not a good idea on a lift most times. Shoring up both left and right sides of the lift with another braced piece of metal will go a long way.

The clicking may be alleviated by using rubber bands to assist the lift. As you lift higher and the lift get vertical, the weight distribution changes a bit. The first joint where you have the big motors carries a bunch of weight. You could also be getting some torsional twist on those points as you lift up and that coupled with the cantelevering could be causing some separation of the gears.

Remember the gear touch point is pretty small. It’s just along the face of the gear teeth. You need good contact there to transfer the force.

@biglesliep

• in each segment of your lift you need cross-bracing. Just bracing once in one segment isn’t going to do it.
• on our lift, my team has 1 or 2 c-channels spanning the gap (in different areas) as well as 1x pieces that cross in an X shape, attaching left side to right side. The 1x pieces are great because they’re lightweight and flat, and are still effective.
• my team also has “self”-bracing on each vertical segment (from chassis to first gear; from 2nd gear to top gear), so that we have teeny 1x “X” bracing between the 2 c-channels comprising each side of the lift. Example: there are 2 c-channels going up from the chassis on the left side of the robot, with the gear sandwiched in between them. Where we can fit it, we have little 1x "X"s connecting these c-channels.
• rubber band triangle won’t help your lift go up straight, but it will help your lift go up, period. The concept is that the triangle method provides continuous tension through the whole range of motion of the lift, not more when it’s folded & less in the middle. My team had to add a little appendage to one of the c-channels for the top point of the triangle; you’ll just have to play around with this to find a setup that gives you “neutral buoyancy” – the lift stays wherever you put it, without motor help.

@Jasper_MCC

In general though, friction is your enemy. You can counter-act a little extra weight with more rubber bands, but friction is never good.

Symmetry is very important, not just weight left-right, but also the length of the bars. If you have a longer bars it can cause the geometry of the lift to change as it moves, making the lift “non-linear.” An ideal dr4b has all 4 bars identical lengths. Changing the top 2 to be shorter or longer than the bottom 2 will cause the lift to “drift” forward or backward as it goes up. Longer top means forward, shorter pulls backward.

Another issue to watch is wobble. Now this seems like tightening the joints would make it wobble less, and it does, but it also make the lift get “stuck” leaning, which then get worse the more it tries to fix it. So by making the joints looser, the lift can fix itself easier, which overall decreases wobble. And cross bracing is important, of course, but not always easy to do if the middle of the lift has to be open.

Those are the 3 biggest things to watch IMO.

@technik3k

… the best place to put motors on the full size DR4B is in the middle section.

The weight of the motors is not going to be a large factor, given the total weight of the rest of the lift. That is usually taken care of by rubber banding the lift such that when there is no game objects it would take almost no force to bring it up, because rubber bands would counteract the gravity.
…
Example of the well crossbraced and rubberbanded DR4B from this thread:

full res

@josh_siegel

… there is always room for improvement so I will suggest some stuff at the end. The reason why it would be leaning to one side could be due to many reasons but will most likely go away if you employ these strategies:

1. Make sure your lift is as symmetrical as possible. I noticed you are using aluminum angle as the bottom bars on 1 side and c-channel on the other. I would change that to c-channels on both sides. Also make sure your angles are exactly what you want them to be (ex. 90 degree angles for a rectangular gearbox, if it isn’t than the holes won’t be exactly lined up causing more friction).
2. Speaking of friction try to eliminate that as much as possible. Any little difference between the sides can cause one side to need more power and therefore sway. This could be caused by the symmetry difference, bent gears, bent axles (even the slightest bend can cause a huge difference), etc… what I like to do is disengage the lift from the motors and feel by hand how smooth it is… it should be extremely easy to lift with just a finger. Also once everything is extremely smooth I add some white lithium grease just to make it even smoother (you would be shocked at how much this helps)
3. On the bottom bars I noticed you have a random 84 tooth gear on the bottom most bars on each side. There is no need for them so I would just take them off.
4. I also noticed you are using axle joints on those bottom bars, you should always use single rotating screw joints. There are a lot of forum posts already about these but essentially one piece of metal has the screw directly attached to it so it only rotates with the metal and the other piece of metal has the bearing so the screw only rotates in that bearing keeping it low slop and low friction. Make sure to keep joints as small as possible also.
5. Take the other’s advice with the X-braces! Those are SO helpful! I attached a photo of an old robot of mine showing the x-braces to see what they are but they really stabilize the lift. You can try linking the gearboxes but these actually help way more.
6. Once you are done mechanically stabilizing… very important that it doesn’t actually need this but as a backup I used to like to use encoders on each side of the lift to sense its position and correct for it using independent PID for stabilization, but this is not necessary and you should only implement once it is mechanically stable as a backup.

full res

[333A]

Rubber Banding Resources:

@meng

This triangular method is more than just about providing tension. The main intention is to achieve uniform tension throughout the lifting and and retracting.
There are lots of discussions abt this during sack Attack.

@callen

I was thinking about the standard advice on applying rubber bands to a DR4B. I think it’s a little bit off. The whole triangle thing is clever, and I’m not saying to avoid that. I’m saying the targets seem to be incorrect.

Why? Maintaining uniform force on the lift is not desired, nor is uniform torque. Aiming for this is incorrect to begin with. What we really want is to provide the most torque when the bars are horizontal and less as the bars are more vertical (toward the top or bottom). And, unfortunately, we always end up with the most force from the elastics at the bottom since all the elastics are trying to lift the mechanism the whole time.
…

@meng

What I am saying is that this uniform tension rubber-band system (UTRS or triangle method to most ppl) is misleading, this is because what we are trying to achieve is not uniform tension (or force), but rather uniform acceleration (as much as possible).

What all of us can agree is that the lift will definitely need more force when it is going up as compared to going down (with gravity acting on the lift as well). But what we are looking at is to get an as uniform resultant force as possible, so that the lift will always be accelerating at about the same rate at every point of its motion.

@meng

There are actually many teams that did it well.

Uniformly Tensioned Rubber Band System Analysis/ Guide

this is the original idea.

@therealcedz

Hello vexforum,
Due to popular demand, I thought I’d explain a little about uniformly tensioned lifts and why they are useful. I’ve explained the uniformly tensioned rubber band system (UTRBS) in my robot reveal, but as the pictures are not working and editing does not work, I thought I’d go more in-depth.

As you all know, adding a rubber band tensioning system to a lift is very important to increase the amount of game objects the lift can carry, to reduce strain on the motors, and even to change the lift’s gear ratio to a faster one.

See the rest of @therealcedz UTRBs post...

Most teams use this sort of rubber band system on their lift (4 bar, 6 bar, 8 bar, etc.):

This system is great due to complexity vs. effectiveness. Just by putting a couple of pieces of metal (in this case, standoffs and screws) and rubber bands, the stress on the motors is greatly reduced.

However, some of you may have come across some flaws with this sort of tensioning system. The rubber bands have a greater upward force when the lift is at the bottom, while the upward force starts to diminish while the lift rises. What this means is that as you lift upwards, the assistive force of the rubber bands start to disappear, as the motors begin to have to do more work. The lift then reaches a point where the rubber bands are completely slack and has no assistive force on the lift.

I created a graph to better illustrate the situation:

Obviously, the numerical values are not accurate as the rubber bands won’t be producing a 100N of force on the lift, but the concept is the same. The Graph also may not even be linear, but the point is that the force diminishes as the lift angle increases.

In addition to the fact that the rubber bands do not work effectively when the lift is raised, high upwards force near the bottom of the lift is also not ideal. With no game pieces in your robot, the lift may start to rise on its own because of the strong upwards force of the rubber bands. One may combat this problem by taking off rubber bands, further reducing the effectiveness of the rubber bands. Others may put a small constant motor value in the code ( while (lift is down) motor value = -10; ) but this is still not ideal.

An ideal graph would look like so:

Constant upwards force regardless of the position of the lift.

My discovery of the uniformly tensioned rubber band system (UTRB for the sake of the phrase’s length) made its way during the 2012 gateway season. While creating a pneumatic lift, I discovered that a UTRB was absolutely necessary due to the fact that pneumatic pistons are quite weak, but also have a constant force along its stroke (save for minimal amount of loss force due to the fact that air gets released every time you activate one). After the robots completion, the robot was able to lift 6 game pieces (3 pounds) to 30” and still be able to bring the lift down with 0 pieces (no weight) all while having a pneumatic lift. To put this in perspective, the pistons could not lift the manipulator up at all without any type of rubber band system. This should demonstrate the effectiveness of the UTRB.

How it works:

Let’s look at the UTRB when one’s lift is all the way at the ground.

If you look carefully, you can see that the rubber bands almost cross the pivot point of the lift.

This means that the force acting on the lift by the rubber bands is very small.
R (crossproduct) F = Torque
Or
R sin(theta) F = Torque.
When theta approaches 180, sin(theta) approaches 0.

Now when the lift is halfway up:

sin(theta) will be greater

When the lift is at the top:

Sin(theta) is the greatest here with a value of 1

Now coupled with the fact that the force of a rubber band decreases as the length decreases and the value of sin(theta) increases as the lift increases, what we get is a(n almost) uniform torque (upwards force acting on the lift).

Here is a video demonstrating the effectiveness of the lift:

Golden State VEX Robotics Competition Final Match - YouTube

Interestingly enough, during this comp, I noticed that another team had come up with this type of tensioning system. One of 1437’s viewpoint robots had this tensioning system in the back of their robot. (If you look closely enough on the red side, you can see that the back of their robot has a bar jutting out of the back of their lift, which is the same UTRB, but just located in the back).

Now in 2013, John Ma and Kevin Li from WASABI used my tensioning system but in a much simpler way

And here is a video demonstrating their lift:

Uniformly tensioned lift - YouTube

The picture, being the more updated version, demonstrates how they only used a couple pieces of metal rather than my original heavy structure (made with a bunch of straight bars and standoffs). Their structure reduces the weight of the structure and I believe this is the simplest it could become. (Use this structure is what im saying basically).

By the way, if anybody is interested, here’s a link of their reveal and pictures of their amazing robots which they go more in-depth to.

1492 WASABI Post-Worlds Reveal

The amount of rubber bands one should use in my opinion should be enough to counter act the weight of the manipulator in addition to some game pieces. For instance, in our gateway robot, when all the air was released from the pneumatics, the lift would start to rise on its own due to the tensioning of the rubber bands. In the case of a motor lift, the idle torque of the motors should be the factor that holds the lift down. In this way, more game pieces could be lifted up (great for high load games like sack attack).

Granted, this tensioning system may not be exactly uniform, as the value of the force provided by the UTRB may waver, but I believe that the deviance is negligible. Some members may do some physics to figure out the exact point to mount the rubber bands to achieve the most uniform tension, but I think it is quite difficult as it requires maybe an upwards of 4-5 variables to solve for.

Heres some more pictures of the UTRB if anyone is interested: http://imgur.com/a/47gnY

Sorry about the quality of the pictures, as they were uploaded to facebook, then uploaded to imgur for the purpose of this guide

Alright! That’s all there is to know about UTRB’s. Thanks for reading, and I hope this helps teams in their quest for awards or yearning for knowledge. If you have any questions, feel free to post below.

@antichamber

Ok, I’ve remade the rubber band calculator! I’ll make a tutorial video soon, but I’ll make a simple explanation for now. Here’s what the different colored curves mean:

• RED: Actual force curve of a doubled up VEX #64 rubber band, X-axis = distance, Y-axis = force
• ORANGE: Distance between banding points, X-axis = angle, Y-axis = distance between points
• GREEN: Distance between banding points scaled by band curve, X-axis = angle, Y-axis = scaled distance between points
• PURPLE: Output force onto lift, X-axis = angle, Y-axis = force

The purple curve is most important curve, and this is the line you will focus on. If you want the same amount of force for the entire specified motion range on the lift, you want this to be completely horizontal between the pink lines. If you want less force at the very bottom of the lift (this allows you to have more lifting force overall while not having to force the lift down continuously while it’s at the bottom)
https://scratch.mit.edu/projects/235244490/#player

Best rubber bands (tensile strength-wise) to use for a lift?

[64540A]

Where was this in ITZ? XD

Jokes aside, I think that this is a really good resource for new teams that don’t know where to start.

[333A]

We didn’t exist during ITZ, and thank you.

[prathusa]

Why didn’t you guys show up to Mundelein? It looks like your bot is complete.

[333A]

We decided to scrap that bot. We were trying to make too much happen in too small of a space.

[AperatureLabs]

Sweet baby jesus you madman. I love it.
Do you mind editing your post if people provide good additional resources? This is the most thorough and complete dr4b post I have ever seen, and being that vex has HORRIBLE BASICALLY UNUSABLE FLIMSY FRICTION BASED LINEAR SLIDERS we will never see the simpler linear lifts used in most other robotics, so linkage based lifts are here to stay.

Also, I would like to say that using the new 4-post nut retainers as the base of you screw-shaft is a good trick for getting even more consistent geometry with little added parts. I know that centering screws is a challenge and the shaved down bearings are clever, but the nut retainers are super fast, and do a great job both centering the screw and spreading out the force.

If anyone has programming recommendations, I would like to see a collection of resources for that as well. Programmers may not be aware of how necessary learning pids are when creating a lift. The ability to recall preprogrammed lift heights, make small changes to height without running the motors at 100%, changing the acceleration profile of the drive train based on the height of the lift, or even combining actions like rollers or claws automatically running/opening as the lift stacks or unstacks objectives. Additionally, these pids make autonomous routines so much easier and reliable. You can keep it easy, or look into temperature management, and using the brake function upon decent to help reduce the amount of current used. This is one of the easiest ways to get really creative and have a positive impact on your robots performance without needing to know a ton of math.

[technik3k]

Great tutorial @333A!

I am going to print it and give to every team in our club who is building DR4B or DR6B lifts.

Please, keep up this good work making video tutorials, which I’m looking forward to watch!

[James6555]

I just realized that the thread title has a typo, @Drow can you fix this?

[SaltyCB]

this is a great resource wish i had it last year, one thing to add always use C-Channel i tried making a lift with angle bars and they are too wide. you want your lift to fold up small and use as little space as possible. If you look at some of the pictures the clearances are less than a centimeter. that is what you want so you can add stuff like a tray to the lift

[64540A]

The person who made the thread can change t themselves @333A

No need to message drow

[AperatureLabs]

@Drow can we get this post pinned? It is a shining example of the quality content we want to see more regularly on the forum. Furthermore, if it isn’t stickied, it will inevitably get buried by posts including (but not limited to) people asking for help with their DR4B Lifts.

[AperatureLabs]

@333A I have a few suggestions.

1. Replace the “1-bar lift” with “2-bar” linkage since the tower counts as one in both the 2 and 3 bar linkages.

2. I recommend using the phrase “screw-shaft” when describing that assembly since it gives that very important building process a proper name that people can call it. I want builders to learn from this techniques that they can apply elsewhere in their builds, and names are good ways to make people remember things.

3. Investigate the use of the new nut retainers in construction, as they make much of this build way easier.

[Deicer]

We can’t pin every guide, but we can add it to the wiki…

Wiki

Vex Forum Index / FAQ / Wiki The purpose of this topic is to make it easier to find vast amounts of knowledge already available on the Vex Forum and related sites. Any forum user with high enough trust level could edit this Wiki and all contributors are welcome. However, to maintain high quality, everybody has to adhere to the Wiki Style and Guidelines, detailed below. Please, DO NOT CREATE NEW POSTS in this topic, unless you have a prior approval from the Wiki maintainers team. Also, please…

[AperatureLabs]

@Deicer

We can’t pin every guide, but we can add it to the wiki…

It would be nice to have some way of nominating or recognizing quality posts as worthy of putting into the wiki. Maybe a regularly (monthly) occurring wiki-nominating post, closed group, @shoutout, or form.

Or just starting a Best-Of thread for sharing the most informative posts you come across. IDK, what do you all think?

[JCampodonico7328]

Is there an official parts lists?

[Railgunawesome]

There are no official parts lists. Use whatever (almost) you want. Just please dont use steel.

[RNA]

Steel will make you DR4B bad and very heavy. One of our teams did one out of steel and lets just say that when they tested it… teeth on gears were destroyed.

[kmaster]

someone on our school team is building a half side steel half side aluminum double dr4b with low strength 60 tooth gears with 4 legacy motors…