I use a standard 82° countersink similar to this one:

My main suggestion would be to make sure you have a good hex key that is a tight fit and not rounded or worn so that the cap screws do not get damaged, if the cap screws get rounded out you will likely have to use an extractor to get them out and then replace them with new screws. Once you have a hex key with a tight fit I would suggest tapping with a hammer or possibly using a small cordless impact tool with the correct hex bit.

Looks good so far, your J3 chain looks a little far away from the arm, you may want to reverse the sprockets so that the chain is close to the J2 arm. thanks for posting and let me know if you have any questions.

Builders of the AR2 or AR3 robot are free to use any gripper of their choosing. Initially I did not include the SMC gripper I was using in the BOM but added it by request. I can add a solenoid valve to the BOM if that helps but there are many options people may choose for a solenoid valve. Please also see chapter 5 on options for a gripper. The SMC gripper has an operating range of 22 to 102 psi - the pressure you choose will depend on what you need for your application. I am running mine at 80 psi. Most automation equipment systems supply regulators are set between 80 and 90 psi. I am using a $50 3 gallon compressor from harbor freight tools. https://www.harborfreight.com/air-tools-compressors/air-compressors-tanks/portable-compressors/1-3-hp-3-gallon-100-psi-oilless-air-compressor-97080.html. This air compressor is a bit loud though... Another option I was thinking of looking into was an 18v cordless compressor similar to this one but I have not researched all the options - this is just one possibility. https://www.homedepot.com/p/RYOBI-18-Volt-ONE-Cordless-1-Gal-Portable-Air-Compressor-Tool-Only-P739/305269932.

hello, 512 is correct, 512 / 2.56 = 200 steps per revolution of the motor. The mult value is just part of the calculation.