[Dprglist] IRON REIGN robot presentation - Today at Noon

John Swindle swindle at compuserve.com
Sat Dec 17 14:26:24 PST 2022

Sorry to hit you with a lot of videos, but I found another example of nice response with a long arm:
>From 10:46 to 12:15 in https://www.youtube.com/watch?v=v8eeWENXvG4
It's not about mass in the base. It's not about stiffness in the arm even though it is stiff. It's about controlling the response, even to the extent of having the base provide controlled recoil.
OK. Back to sleep now.
John Swindle
-----Original Message-----
From: John Swindle <swindle at compuserve.com>
To: dprglist at lists.dprg.org <dprglist at lists.dprg.org>
Cc: John Swindle <swindle at compuserve.com>
Sent: Sat, Dec 17, 2022 3:57 pm
Subject: Re: [Dprglist] IRON REIGN robot presentation - Today at Noon

Karim and Iron Reign Team,
Thank you very much for the DPRG presentation today. Big competition!
You asked what filter another FIRST team used to make their big robot stop on a dime without wobbling. This is the sort of response I was referring to:
Although the robot is heavy, about 160 pounds, and even though most of the weight is in the base, nevertheless it is quite tall and the cargo it carries has mass. It accelerates and stops very quickly with very little wiggle. It drops its cargo with no residual movement in the cargo.
Another example shows how quickly the platform settles after harsh movements with lots of moving metal:
Along with all the stuff moving at the same time, I like how quickly the grappling arm calms down after being flung open at the end of the contest.
Not related to my comments, but I love the whiffle balls in the competition at the end of the next video. I saw them compete in Houston. Loud cheers when the balls started flying!
Regarding wiggling towers: I know some of that was determined by giving the platform impulses of movement, from the motors, I believe, not from hammers as I said, and recording the response of the entire robot.
Then the desired controls are filtered with an inverse of the response before being sent to the actuators and motors. I think that can be translated to PID instead of using a filter. I think that is what you are doing.
I think someone at DPRG showed how to automate the PID tuning by looking at the reactions (Might have been you!). You are probably doing that also.
I spoke up because it seems that tuning and tweaking are often done ad-hoc or by trial-and-error instead of by knowing the system response. That's just an observation. Not trying to comment on what you are or are not doing. When you don't know the actual system response, the deconvolution can easily makes things worse!
I don't make motive systems. I play with audio. I use the cheapest stuff available: 50-cent speakers, 79-cent microphones, cheap consumer-grade audio adapters, lousy amplifiers. Then I force those things to act the way I want them to act.
So, there are at least two classic way of forcing something to do what you want, so long as you don't exceed some limits: transmitter equalization (Tx EQ) and receiver equalization (Rx EQ). I have the luxury of doing either of these because I don't care how the things behave as long as I get a usable result. You don't have that luxury because you can't grab the pole and hold it steady while you drop a cone on it (which would be Rx EQ). Hmmm... Can you do that?
In my case, Rx EQ puts greater burden on the robot to process the audio before using it. I greatly prefer Tx EQ. The pings are not filtered by the transmitter: they are simply screwed-up (convolved) before they are stored in the wave file. No processing at runtime.
I choose a (not convolved) waveform that I think will give me best resolution with minimum ping width and lowest human-audible amplitude, then pass that through the system in the arena, note the difference in the recorded result, and then start tuning the transmitter.
I put all that stuff away a few years ago, so I don't have a demo to show. Maybe I will put it back together again.
Sorry for the long answer, but maybe something will help at some point. And sorry if I am repeating stuff I've written before.
Thanks for sharing your development process and your current status today!
Good luck!
John Swindle
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