Fabricators in North San Diego?

Anyone who is good at knocking out quick fabrications of things with bearings, metal parts, and tubes in NC SD (e.g. Escondido, San Marcos, Vista, Valley Center, Rancho Bernardo, San Elijo, etc…) and might be interested in trading work for: Firmware, Electronics, Robotics, Eggs, access to tools (Tiny CNC, small Laser, 3 pretty good 3D printers, etc…) or whatever else we can settle on, e.g. my undying gratitude? LOL.

My lack of fabrication skills is just slowing this project to a CRAWL and I really need to get it over with so I can prove or disprove my theory. Requirements list is under “Mechanical Design”

P.S. NO. I do NOT wish to discuss the theory! Thanks, anyway. I wish to prove or disprove it. I’ve already seen it work VERY well on the robot, with 3D printed encoders and an FPGA, I just want to know if the lower speed of a microcontroller will also work.

I’m afraid I just cant help with bay area fabricators…

And I cant really help with not mentioning your research either, on account of having a BSC in Cybernetics and Control Engieering…

Have fun with what you are doing! and you are right in that a microprocessor can take over from a FPGA in the sort of stepper based ‘move to position and hold’ control system the dexter uses; when it was designed (2010’ish) their choice of mcu was somewhat limited; fast controllers (STM mostly) ones cost more than a FPGA; these days fast 32bit mcu’s can be bought for 10 cents.

However… there are many kinds of control system; be careful what you are comparing and investigating. Dexter uses stepper motors and stepper motor driver modules, not DC motors.

This means that for each joint in the dexter robot there are two motor control systems in play.

  1. The main controller with optical encoder; this just feeds a stepper motor driver with ‘direction’ and ‘step’ pulses and is the primary motor control loop; It does not need to worry about loads etc because it is solely concerned with moving to a position.
  2. The stepper motor drivers; these are also control circuits. And they use very classic PID controllers (based on feedback from the inductive load on the coils) to make the motor itself move to the desired microstep position.

It’s the interplay between the two that allows the robot to move smoothly to position without overswinging or oscilating in a meaningful way.

And, actually, there are very tiny overswings and oscillations happening at the stepper motor level, but the gearing, drivebelts and stiction ensure this is never translated into the joint. You may hear it as a occasional whine from the steppers while stationary.

Edit: I have read this; so I get what you are doing :wink: and it seem very worthwhile. But if you are dropping the stepper motor + drivers from the system you will probably find you do need all three PID factors tuned correctly to get it to hold position properly.

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It’s not clear to me how much machining you need with the fabrication. I’m guessing some at least for precision bearing fit. (I don’t know why 45° cross roller bearings are important to you; I’d spec widely-available angular contact bearings which are at a much shallower angle and thus easily adjusted for desired preload, and if I didn’t like that cost I’d just stack up precision roller and thrust bearings. 45° cross roller bearings I’d expect to be a pain to get preload set right, given your general desiderata.)

I haven’t seen a lot of metal fabrication projects posted here, and the population of machinists (hobby or otherwise) is also not high here, even though I do enjoy posting here about my own hobby machining work. (I personally do so little fab that I’ve been out of MIG shield gas for years and haven’t had the tank re-certed and filled…)

There are orders of magnitude more hobby machinists at Forum list | The Hobby-Machinist and it’s an active and friendly community. I’ve certainly seen people there listing locations in southern California including the San Diego area. Some forum members also enjoy fabrication; I’ve seen posts involving both machining and fabrication.

My suggestion in any case would be to include a brief summary of what you are trying to accomplish, rather than assuming that everyone will click through and read and click around to understand the context of the request. :smiling_face:

I’d also suggest that at least cartoon CAD would make your requests clearer. I read your requirements list and didn’t come away with a sense of what you are looking for.

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I think you are right about the cross roller bearings, and I should update the spect on that point. Thanks for the referral.

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