Wow, impressive, Chuck! I feel humbled in the presence of such talented folks, coming more from a journalist/writer side of things than the engineering side. I do have a fascination with technology and innovation, though, so I suppose that helps. Even if I can't do it, I can at least admire it and write about it. I think if other staff members are developing cool things, they should speak up and write about it!
We've had some pretty amazing people on the staff over the years, Liz. Jon Titus, who retired from Design News only a few months ago, is actually credited with building one of the first PCs, the Mark-8 in 1974, which appeared on the cover of Radio Electronics (unfortunately not on the cover of Design News). It's now on display at the Smithsonian Intitution in Washington D.C., which gives an idea of its monumental significance. That said, I don't remember any of our staff editors writing an article in DN about their own invention. To my knowledge, Cabe is the first.
I was wondering about that, Chuck. I haven't been around Design News that long but I was also wondering if it was common for an editor to also be an inventor and write about his/her own work. I think it's really interesting and cool, but personally I can only write about engineering, not actually invent anything or do anything too technical! So this makes me extra impressed about what Cabe has done. But perhaps we should do more of this if there are equally inventive people on the writing staff.
78R, You propose an interesting alternative. But the problem of stepper motors slipping steps happens much more at higher speeds, rather than at starts, as long as the load is within the ability of the motor. So the control could be quite simple, just to add the additional torque whenever the velocity command exceeded some value. No need for a high level of control there. And another option would be to raise the stepper motor voltage when the speed command went above some setpoint. That would be a lot simppler mechanically and probably only require adding either a single relay or a switching transistor. And the voltage controller could be driven by the velocity command amplitude, so there would be no extra computer control functions involved. That is about as simple as I can think of.
Excellent comments, William K. Cabe does walk the walk and talk the talk of a design engineer.
Building on your idea of torque assist for the servo: Adding a brush-type DC motor would make the State Machine more complex and would likely require multitasking to control two types of motors and monitor position, suggesting an RTOS. Thus, the Raspberry Pi would take on this burden, not the Arduino. What do you think about providing torque assist via a latch solenoid engaging a twist spring just before activating a servo? There could be one spring for forward assist and another for reverse assist. The torque would be just enough to supplement the servo's effort. This might be a simpler approach, though I haven't thought through how to rewind the spring.
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