1lb Combat Robotics

Current and Previous DPD Robots

DPD Robots

1LB Starter Guide

The premise of this guide is to help builders who wish to 3d print robots, primarily for competing in the iRobotics 3d printed 1lb competition, Design Print Destroy (DPD). It is expected that readers at least have some basic knowledge of 3D printing already.

Introduction

Our primary concern in combat is going to be the strength to weight ratio of the parts we are printing. This is affected not only by the material choice of the part, but also many settings decided during printing such as layer height, infill percentage, infill geometry, outer wall thickness and layer adhesion. When creating these parts, we have to balance ease of printing, time to print, and the final part tolerances and strengths to create 3D printed parts for the competition. 3D printing also comes with its own unique challenges; parts often are stronger in certain directions, dimensionality is significantly worse than machined parts, and artifacts from the printing process often necessitates secondary machining and rework.

Printers & Processes

Note that for the purposes of the DPD competition and most other plastic antweight competitions, FDM printing is the only legal option.

FDM

Fused deposition modeling is by far the most popular consumer and prosumer 3d printing process. There are many printers and guides available, and this process is the focus of most of this guide. While it often lacks great resolution, and cannot be scaled up, the ease and flexibility afforded by the process makes it very popular. Our current favorite printer for the value is the Prusa i3 MK3. There are some fairly cheap printers that are based off the i3 that are great for beginners as well.

Examples: Prusa i3, Ultimaker, Lulzbot

SLA

Stereo Lithography uses a liquid resin and a curing laser to create models in a layer by layer fashion through a process called photopolymerization. SLA can create parts with high resolution and dimensional accuracy, but the resin is expensive and not particularly strong.

Examples: Form Labs Form 2, Peopoly Moai

SLS

Selective Laser Sintering uses a laser to sinter a powder material to create a 3d model. It can be incredibly accurate, and has the ability to create a variety of complicated parts since the unsintered powder acts as support material. SLS is quite expensive and has few consumer options, and often the only available material is nylon. It has a lot of potential for higher volume rapid prototyping, but is generally not the best for one-off parts.

Examples: Form Labs Fuse 1

Metal

Currently in development stages, there is not much available right now that could be placed in a machine shop. Past systems have been similar to SLS but with a metal powder, though how the powder is deposited is different.

Examples: Desktop Metal , Markforged Metal X

Hybrid

Some systems print differently, of particular note are Markforged printers, that have the ability to weave solid fibers like carbon or fiberglass to create strong composite parts. While these parts are significantly stronger than plastic only parts, note that the printers and consumables are quite a bit more expensive, so if the extra cost is worth it really depends on your wallet.

Examples: Markforged Mark 2

Materials (FDM)

Standard Materials

These are some fairly standard materials that are not too difficult to get your hands on. For the most part, consumer grade printers should be able to print these without tooling changes, though some materials are easier to print than others. From an iRobotics perspective, our Ultimaker 3 should be up to printing all of these out of the box, though Ultimaker does not publish slicer configs for all of these.

PLA+

Polylactic Acid+: Not a standard spec of PLA, meaning that it will vary between brands, but generally they are PLA blends enhanced for greater toughness with less stiffness and reduced brittleness. Recently, these PLA+ materials have become very popular in DPD/other plastic 1lb competitions, and are regarded as the optimal choice in terms of durability and strength. These materials are generally a great option for 1lb robots, with specific brands of PLA+ being known as highly durable. Specific brands of PLA+ that are known to be strong are the PLA+ from Duramic, or the "Super PLA" from Overture.

PLA

Polylactic Acid: In recent years, this has become one of the most popular filaments on the market. While it is not particularly strong, it prints well at lower temps and does not have warping issues. Additionally you can bridge gaps better, and it flows easily enough that you can print at relatively high speeds.

• Pros
  • Prints easily and quickly, doesn't have warping issues.
  • Cheap (Hatchbox sells this ~$20/kg)
  • Works on any printer, even those without heated beds
• Cons
  • Weak / Brittle
• Approx Print Temps ( Nozzle: 210, Bed: 55)
• Additional Tooling Required (None)
• Conclusion: Not really suitable for combat robotics, but if it is all you have can work.

ABS

Acrylonitrile Butadiene Styrene: ABS is probably one of, if not the, original filaments used for consumer market printers. It is fairly strong, think middle of the pack. It is one of the most popular thermoplastics in the world, mostly used for injection moulding. Unfortunately it tends to warp while printing, and getting it to adhere to beds can be difficult without an enclosure or specialized build surfaces.

• Pros
  • Strong and impact resistant
  • Cheap (Hatchbox sells for ~$22/kg)
  • Most printers have configs for it
• Cons
  • Higher print temps
  • Large warping issue
• Approx print temps (Nozzle: 255, Bed: 100)
• Additional Tooling Required (None, enclosures help with warping issue)
• Conclusion: Decent, is a good starter material that is fairly accessible. Printing it can be difficult for cheap printers.

PETG

DO NOT USE PETG FOR COMBAT ROBOT FRAMES/WEAPONS

While true that it has better strength/toughness compared to pure PLA, it exhibits a extremely brittle failure mode where the material will crack and fracture instead of gouging or deforming like some materials like PLA+. Robots that are made of PETG will be easily broken apart by kinetic weapons like spinners which impart high dynamic forces which will exceed the strength of any plastic.

Polyethylene Terephthalate w/ glycol: A fairly common polymer that is used to make plastic water bottles. It bridges the gap between ABS and PLA. It has good impact toughness, but is fairly easy to print. Not that much experience printing it at iRobotics, but many people use it as an ABS alternative.

• Pros
  • Strong and impact resistant
  • Cheap (Hatchbox sells for ~$22/kg)
  • Prints on most printers
  • Good layer adhesion, many robot frames fail cracking along layer lines
• Cons
  • Not as strong as ABS
  • Hydroscopic, absorbs water from air, tips below on keeping filament dry.
• Approx print temps (Nozzle: 255, Bed: 50)
• Additional Tooling Required ( Must be stored properly in between prints)
• Conclusion: Should be explored more, some of its properties( toughness, more flexible, good layer adhesion) may lend themselves really well to combat.

Nylon

Nylon is a very tough polymer that is also very non-reactive. It is commonly used in zipties, and is fairly flexible. It comes in many blends, mainly Nylon 6 and Nylon 12 derivatives, some of which are easier to print. It is considered fairly hard to print. It does not like to stick to the bed, and it absorbs water if left in a humid environment.

• Pros
  • Very strong, very high impact resistance
  • Available in different blends, can be changed to the application
• Cons
  • Expensive, price varies by blends
  • Hydroscopic, tips below on keeping it dry
  • Difficult to get prints to adhere
  • Flexibility might be a liability in combat, over flexing may compromise robot internals
• Approx print temps (Nozzle: 240, Bed: 50)
• Additional Tooling Required ( Must be stored properly in between prints)
• Conclusion: Could be useful in combat, particularly in parts where impact toughness is desired above all else, and the flexibility issue is mitigated.

Note: Taulmann sells a variety of nylon filaments that a easier to print, such as Taulmann Bridge

Polycarbonate

With a brand name of Lexan, polycarbonate is a very tough polymer that is possible to print. We use it to form the walls of the DPD arena. It is extremely tough without being overly flexible. It sticks somewhat to few print surfaces, but it even more prone to splitting and warping, and as such needs a very high extruder temperature to have good layer adhesion. To print, the printer needs to maintain a very high bed temperature, upwards of 135c in some case. On the prusa i3, it sticks fairly well to the PEI build surface at 120c. Enclosures also help to prevent warping and keep a higher stable bed temperature.

• Pros
  • Probably the strongest standard filament available
  • Prints on our printers, with some headaches
  • Isn't too expensive, more than double ABS/PLA prices though.
• Cons
  • Limited options of places to buy from
  • Requires extreme print temps, many cheaper printers will not be able to print.
  • Warping and other issues can be tough to mitigate.
• Approx print temps (Nozzle: 270, Bed: 120) <- some blends require even higher temps.
• Additional tooling required ( Printer may have to be modified to reach high temps)
• Conclusion: For people with capable printers, PC can be a really good choice as a logical next step after ABS. It is only available from a few locations, and in a limited number of colors, but the toughness gains may be more than worth it in the 3d printed combat robotics space.

Note: PC-Max from Polymaker good reviews, and is blended for somewhat easier printing.

Exotic Materials

These materials have special additions that give them a wide variety of properties. They tend to be more expensive, and not that many are useful for engineering or combat applications. Examples include filaments that have specific textures, flexability or vivid colors. There are even materials made from organic fibers like hemp. There are a few however that offer improved performance in combat applications, a few of which have been outlined below. Beware that some of these filaments are highly abrasive, and as such require special nozzles.

Nylon w/ Chopped Carbon Fiber

As outlined above, nylon is extremely tough, but has a few drawbacks that limit it's performance in combat. One of these is flexibility. Adding chopped carbon fiber to the blend helps to improve part stiffness, prevent warping, and significantly improves the strength of parts. Markforged even claims its proprietary Onyx blend comes close to 6061 Aluminum in strength to weight ratio.

• Pros
  • One of the strongest filaments got even stonger
  • Easier to print than traditional nylon in some ways
• Cons
  • All the difficulty of printing nylon
  • Expensive ( $86 / kg)
• Approx print temps (Nozzle: 240, Bed 50)
• Additional Tooling Required ( Hardened extruder nozzle, enclosure)
• Conclusion: As tested one of the best filaments for combat robotics. It can be pricey, but the cost can be well worth it in terms of toughness and rigidity. Special care needs to be taken when using this filament, but advanced users should be able to make it work for them. We have had good results printing NylonX from matterhackers, and other alternate suppliers also have good online reviews.

Examples: Onyx, NylonX, CarbonX CF-Nylon

Polycarbonate w/ Chopped Carbon Fiber

Very similar to Nylon with CCF, this PC variant is probably one of the strongest filaments on the market. We have not been able to print and test parts with it thus far, and it seems to only be available from one supplier (3dxtech). As with standard PC, we expect it to be difficult to get bed adhesion. The CCF also increased the viscosity of the filament when liquid, and as such it is recommend that this filament be printed at around 300c, which is hotter than most, including a Prusa I3 can handle without modification.

• Pros
  • Probably even stronger than Nylon w/ CCF
• Cons
  • Even more expensive ($160 / kg)
  • Extreme printing temps required
  • Limited suppliers

Approx print temps ( Nozzle: 280-310, Bed 120)

• Additional tooling required ( Hardened extruder nozzle, thermocouple hotend sensor, enclosure)
• Conclusion: At almost double the cost per kilo than nylon with carbon fiber, PC-CCF may be in the realm of diminishing returns. Once we get a printer running that can handle it, we will conduct some strength tests to determine whether the increased costs and printing headaches are worth it. Maybe only Ultem-CCF or metal could be stronger.

Examples: CarbonX CF-PC

Ultem 9085, Ultem 1010 and Ultem w/ Chopped Carbon Fiber

A family of PEI ( Polyether Imide) plastics manufactured by SABIC, Ultem has even more favorable properties for combat robotics than that of nylon or PC. We aren't going to do a breakdown on it since there is very little literature on printing with it floating around the internet. It is claimed to be strong enough to replace steel/aluminum in some automotive applications. It requires extremely high extruder temps ( 360 -390c). Take note that it is very expensive ($260 / kg), so if you have money to burn and a capable printer, this may be the way to gain an edge.

Settings optimization

Modifying print settings to optimize for different properties can give your robot the fighting edge in combat. Most of our tips revolve around increasing the strength of parts, sometimes sacrificing resolution or print speed.

Infill

Infill is often one of the easiest ways to affect the strength of your finished parts. The lattice structure formed can be incredibly strong one when printed correctly. Both the pattern, and the infill percentage affect the performance of the part. Parts with lower infill, to a point, often have better strength to weight ratios than more solidly printed parts. For instance, we often print our frames and non-weapon parts with a 20% infill, with a cubic pattern. The 3D triangles provide a lot of internal structure, and the lower infill performs well without sacrificing a lot of weight. Additionally, printing the frame as a single uni-body piece provides a lot of strength gains to distribute shock loads. One disadvantage of the lower infill is that when the frame's outer shell is penetrated by a weapon strike, it often critically compromises the frame on that side. Additional hits to the frame will often tear open larger and larger holes until internal components are at risk of being compromised.

Recommended Suppliers

Here are some suppliers that are good to check out when looking for filament. Not all filament brands are equal, and many times paying a little more for high quality filament can lead to significantly fewer print failures, and stronger parts.

Matterhackers

They are part filament supplier, part 3d printer resellers, and part knowledge base. They have a lot of good printing tips and tricks on their website, and also have a good selection of 3d printer upgrade parts. They have excellent customer support, and their PRO series filament is known to print like a dream. Their NylonX CF-Nylon blend is of high quality, and being based in LA means shipments arrive quickly and shipping costs are low to free.

3DXTECH

3DXTECH is a smaller store that is targeted more to industrial and professional use. They resell, and offer a variety of in house blends of filament. One thing they do have though is an extremely broad selection of engineering focused filaments. They don't come in a high variety of colors, but they offer the cheapest high quality CF filled filaments. They also have filaments that are difficult to find anywhere else, such as Ultem.

Hatchbox

Hatchbox is a chinese company that mostly sells its filament through amazon. they carry most common filaments in a wide variety of colors at extremely competitive prices. Plus quick delivery through amazon prime is a plus. Their filament comes with relatively tight tolerances for the price, and iRobotics has had good luck with them in the past. If you need run-of-the-mill ABS or PLA, this is the place to get it.

Upgrades

Here some popular or useful 3D printer upgrades are listed and explained. Not all of the listed upgrades have been personally tested, but this at least provides a jump point for someone looking to improve their printers performance.\