Skip to main content

PnP - a simple "industrial" robot

Watching a typical multi-degree-of-freedom robotic arm can be a joy. Separate from precision welding on car frames, they sometimes seem to have a life of their own, and the way they seem to dance and flow is almost mesmerizing in some cases. PnP ("Pick and Place") was built for a couple of reasons - first, because it was fun, and second, because a number of folks seemed to think it would be hard or impossible.

It started as part of a challenge that involved building LEGO using only LEGO - a hard challenge in the first place, but we were trying to do it with only the parts available in a NXT kit. A lot of folks commented that this would be "very difficult" without some easy mechanism for linear motion, like gear racks... but I wasn't convinced. First, there were other ways to generate linear motion (lead screws, or certain mechanical linkages). And second, I wasn't sold that linear motion was required... so I set out to do it without linear motion, and using only three motors. I didn't finish (close, but no cigar), but what I did come up with was an elegant, and very simple way of manipulating 2x4 elements... or other parts. PnP is a two-degree-of-freedom arm, with a static mechanically leveled "finger" at the end. It can pick up and place 2x4 elements (or larger) and place them somewhere else, as well as activate levers, triggers, or slides. It could push elements together, measure element size (by pushing them against something hard, and seeing how far the arm has traveled), or it's shape (for elements of a certain size, it could be used to actually "feel" the upper profile, or determine where it balances). Since it can position the "finger" to a high accuracy and precision, the motions can be both precise and repeatable - & it's all programmed in NXT-G, with a fairly simple program (one My Block is used to move a specified joint to a specified location, with the speed as one of several variable parameters). Yes, it will maintain it's accuracy over a couple hours... in fact, the LEGO pieces very slowly separating in the framework are a bigger problem.

In this case PnP is set up as a simple color sorter - that's nothing new, there have been lots of those, many perhaps better done than this one. The difference is that PnP is much more general purpose - it could study the sequence of bricks in a pallet, and replicate that pattern from "raw materials" pallets (even unsorted ones), or determine if the pieces it's lifting were 2x4 bricks, or 2x4 plates. Since it uses only one sensor (to determine initial placement), it is free to incorporate several other sensors (like the HiTechnic color sensor here)... and it still has a motor port unused, to perform still other actions (moving the entire PnP arm along a track? Running a "brick press" or conveyor? Use your imagination). It would be very easy to set up more than one PnP arm in a row with their workspaces overlapping, allowing a robotic "assembly line" as items were passed down the row... or have a mobile pallet move along a line of PnP's to have things added on or stacked for transport.

Most LEGO robots have terribly narrow ranges of function - they are designed to do one thing, and only one thing, very well. But that doesn't have to be the case. It will be interesting seeing what EOAT's ("End Of Arm Tools") I can come up with for PnP as well, and just how far I (or you!) can take this.

Anybody want to build an assembly line?

Brian Davis

Popular posts from this blog


2023 is the 25th Anniversary of the MINDSTORMS brand. For 25 years, MINDSTORMS has educated and inspired a generation of robot builders, both children and adults. Unfortunately, the LEGO Group decided to end the line on December 2022. Many ROBOTMAK3RS have been passionately involved with the development of MINDSTORMS through the MUP and MCP programs. Even with the newest Robot Inventor line, several ROBOTMAK3RS were invited to submit additional bonus models that were included in the official app. Regardless of the retirement of a major LEGO robotics product line, ROBOTMAK3RS continue to MAKE-SHARE-INSPIRE using all LEGO robotics platforms available to us. Here is the official statement from LEGO. Since its launch in September 1998, LEGO MINDSTORMS has been one of the core ‘Build & Code’ experiences in the company’s portfolio, carrying with it significant brand equity and becoming a stand-out experience for the early days of consumer robotics and leading to current Build & Code

Celebrating MINDSTORMS with a Remix Part 1

In honor of the 25th Anniversary of MINDSTORMS, we asked ROBOTMAK3RS to combine a LEGO set of their choice with a MINDSTORMS set. Here is what these five ROBOTMAK3RS came up with.  MINDSTORMS Chess Assistant by Arvind Seshan Overview: When you are new to chess, it can be a challenge to remember which pieces go where. Now, you can use machine learning and LEGO MINDSTORMS Robot Inventor to build a tool to help you learn where all the chess pieces go on the chess board. Sets used: LEGO® Iconic Chess Set (40174) and MINDSTORMS Robot Inventor (51515) Review: I really like how the chess set base can store all the pieces underneath and that the board neatly splits in half for handy storage. The chess pieces themselves are very sturdy and well built. My only criticism is the building of the box itself. It was quite difficult to see what pieces to use and since the entire box is made mostly of thin plates, it took a lot of time and patience. I would have liked the storage area to be sliding dra

Celebrating 25 Years of MINDSTORMS

In celebration of the 25th Anniversary of MINDSTORMS, we take a trip through history. Please also visit ROBOTMAK3RS Community every week as we highlight different projects all through 2023 in celebration of the anniversary. Some of the early history is based on the content shared by  Coder Shah  in our  MINDSTORMS EV3 Community Group . Some of the text and links may have been edited from his original posts for consistency and clarity.  1984 - Kjeld Kirk Kristiansen watched a TV program called "Talking Turtle," where MIT professor Seymour Papert demonstrated how children could control robot "turtles" using LOGO, a programming language he developed. 1988 - The collaboration between MIT and LEGO resulted in LEGO TC Logo in 1988, which allowed students to control LEGO models using computer commands. The video shows Papert demonstrating TC Logo. 1990 - LEGO TC Logo was hampered since the robots you built had to be tethered to a personal computer. LEGO and MIT