I built myself a new Robot Buddy!

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[anninrobotics]

Thomas,

Thank you for building the AR4 and highlighting some of its features. I did want to touch on a few of the comments you made. In the overview section of the manual I do mention pre-applying solder to wires being joined together - I find it easier to pre-apply solder or tinning the ends - and then bring them together with the iron rather than trying to hold the wire ends together and hold the solder and hold iron at the same time, not having 3 hands - it helps to pre apply the solder. None of the wires going to the breakout board call for tinning so I'm not sure about your comments on that?

On page 143 I do have some groups of wires soldered together to help group them going to the 3 screw terminals as its a tight fit and difficult to maneuver them into position without them being connected but you could certainly use ferrules in this step if needed.

At one point in the past the design did utilize plug connectors and building a wiring harness. Given different applications, motions and articulations all the low cost plugs I sampled proved to fail over time. With this small arm and the limited cable routing and cable arc lengths, direct solder with the solder joints in strategic locations using heat shrink proved to be more reliable, less bulky, less costly and not as time consuming as crimping and inserting numerous plug pins. The primary goal of this project from day one has been to realize a usable robot and at a very particular price point. I've worked with industrial robots my entire career and its always been a frustration that any usable robot was out of reach. There is an absolute threshold on the price as most educators have a budgetary limit so I have made it priority number one to stay under that limit. This drives many of the design aspects, The motors for example are off the shelf variants and cannot be fully customized without adversely affecting the price. There is a limit as to what OMC can customize on these coming from the factory. The machined components are kept to an absolute minimum and as many as possible are cut from flat sheet material. This also drives the bearing designs and tensioning designs as custom machined threads and spindles for locknuts for example is not in the cards at this price point. It also drives some of the belt selections.

I did notice the belt tension on your build was far too loose resulting in a good amount of play. Here is a quick video of the forced deflection on my build. (well it looks like I cant post a link in comments but I will post in on my channel or the forum) - Making the statement that "This robot arm is neither accurate nor precise, rigid or smooth" seems a bit harsh considering. The AR4 project is always under improvement, its not perfect but like I mentioned to you in an earlier email the robot is designed for pick and place, welding and handling operations. A great deal of effort has gone into this project, I know you have a great deal of experience and a wealth of knowledge in all manner of machines and mechatronics and your design suggestions are certainly well founded but I wanted to explain these aspects of the project, and hope you will convey these points to your audience.

Thank you,

Chris

[MMuraseofSandvich]

4:29 The reason why a tinned stranded wire will fail in a screw terminal is twofold:
1. Tinning a stranded wire will introduce a weak point where the solder wicks into the wire. If the wire doesn't move, this isn't a problem. But if it's part of a moving system, that wire is now much more likely to break where the solder wicked up. Now, I'm told you _can_ get away with tinning as little of the wire as possible, but I've never seen anyone pull that off.
2. Solder is prone to "creeping" under pressure, it's not really meant to hold its shape when it's squeezed. Over time, the soldered wire will slowly deform, loosening the connection with the wire, meaning you have to go back and tighten the screws. I've actually encountered this after about 2 months, and it is a huge pain.

Better to crimp on a ferrule to each of those wires and never have to worry about them until something happens on the other end.

[Audio_Simon]

Hats off 👏 to Chris for managing such a massive product / project. Even writing the guide must have taken weeks.

[Pillazo]

Not sure if I missed the price, but a quick look at the link says its about $1200 for the kit, and $800 for the motors. Not bad all things considering, could certainly help a mom & pop shop get some basic automation going

[WreckDiver]

Having been a developer for a big robot company in my past, that rail design was awesome game changer for us. There are still zero locations, but yes, they are reduced. Next big change for us was 6 DOF Force sensor with a 3D Laser camera...Best job EVER!

[CNCKitchen]

14:57 is the money shot 😅 Does that mean I need to build one myself now for awesome promo shots?

[xanowich]

Instead of tinning wires it is better to use ferrules. Cheap and reliable

[joeanon]

shim the bearings with some foil. when splicing, stagger the lengths to avoid a lump in your cable wrap.

[end_of_]

I've been watching Chris's channel for a few years. I love that his work is getting more mainstream traction! I've been wanting to make an arm for myself since I've seen his channel. His videos are amazing to help understand how things work!

[amoose]

Take a look at the Parol 6. It’s more expensive at around $2300 in kit form but the movement repeatability tests I’ve seen look impressive and it’s open source.

[TheNamelessOne]

Axis 2 and 6 are designed OK. Other axes makes me say "what was he thinking?". Trapezoidal belt for axis 1, 3 and 4. Leadscrew on axis 5... Yes, it moves center of masses down and reduces required torque, but it would be much better to grab beafier gearboxes with higher reduction rate and drive joints directly.
As for electronics, he could install TMC5160-BOB in the back of each motor, connect all of them via SPI, and control everything directly from RaspberryPi.

[elHippieSupremo]

The manual for the AR4 is well worth a read. Love the details put into how all the control hardware is wired together.

[Rob_]

Good "review" of this kit. Even with restrictions I think for this money you get an awsome kit.
@12:33 you say the motors don't meet the backlash of 0.25 degrees but you measure the complete robot, not just the motor, so that means you also measure any play in the bearings.
I use a Kuka KR180 and with that one, motions are also not always smooth. Depending on the load (I have a 30 kg spindle motor mounted as end effector) I can see some jitter during moves and expecially when the brakes are released from the motors there is some movement to compensate for changing load on the motors.
The AR4 is still an amazing development and it does have some nice uses for parts picking applications

[lynspyre]

I've followed Chris Annin's project since de AR2. He's done a beautiful work on that thing.

[leogray]

A point on the software, what you are provided with looks to be on pair with a pretty standard industrial robot arm controller system. Which is great, and it gives all the function you need to make it move. However, what you need to learn is less about specifically this software, or any industrial robot's software, but the systematic knowledge of robot. More specifically to the problems you get at the end where robot doesn't move in the right way, it will all make so much sense after you learn the basics of robot kinematics and trajectory planning.

[kurtnelle]

Oh boy that backlash. I guess I'll wait for AR5. Feedback: Hall effect sensors are more accurate than limit switches. There are even hall effect encoders to check the actuall position.

[Scratchy]

Hi, robotic engineer here. I made this robot a while ago when he was at the AR3 version, this made me learn how important precision machining and zero backlash gearbox is important for robots. Also his kinematic his questionable. While it does work, you need to develop your kinematic with singularities in mind and all the possible configurations of the robot for that position. Instead he limited the joint limit values to avoid having more than one configuration, but this is not optimal, dangerous even.

[zarster]

Kudos on the edit of the video. Appreciate the cutting to match the music.

[jeffmofo]

I've been thinking about building a robot arm. Basically a "3rd hand" setup.
Push a button puts it in free move mode. Then push the button again and it locks in place.
The most generic example is soldering. Position the arm to hold the wire in place and then I can solder it together.

[MarinusMakesStuff]

Awesome, I've been following Chris Annin for around seven years already. Still never got into making the arm since budgetwise I don't have a reason to buy it, but I love his work and this robot arm should really become more popular so maybe it will develop further and further into a really good and solid product. I think this is the best robot arm you can get as a hobbyist. Maybe one day, when I have a disposable income, I will definitely get one. Very happy to see you build one Thomas! :)