Tangential - in the case of low profile tires, I've seen pothole damage where the rim itself was broken. That causes a "flat tire" even if the rubber tire itself survived.

Sure, you can break the rim with a big enough pothole on regular tires, but normally people refer to such an event as "wheel broken/fucked up/gone/etc" not "a flat".

Also why do you need 1uS for motor control? 1uS is 0.1 degrees of rotation at 16,666 RPM if I did the math right.

I don't know much about motor control, is it normal to need that fast of feedback?

>> Also why do you need 1uS for motor control?

It's not that important if you use current sensors on the motor phases. But then you're looking at HALL sensors or a shunt with a very high gain amplifier with good common mode rejection - looking for mV signals on top of a +12V or +48V square wave at PWM frequency.

By using low-side shunts under each half-bridge you don't need the common mode rejection, but you can only measure phase current while the low side FET for that phase is on. That means limiting the PWM duty cycle to ensure that FET is on long enough to measure current, so we trade available voltage range for sample time.

I've also written code to measure all phase voltages with a single low-side current shunt under the whole 3-phase bridge. That requires careful phase shifting of the PWM signals and very fast conversion time, but you don't have to compromise available voltage range 0-100 percent duty cycle is possible.

Typically we run the control loop at PWM frequency, but the measurements need to be faster than that.

You can also have two shunts per phase, one low side and one high side. The "hall" "shunts" are pretty good though.

That's wild. Would never have guessed.

Field-oriented Control schemes modulate phase currents at high frequency; the feedback loop must be much faster than the motor phases. Until fairly recently, this stuff was the exclusive province of dedicated ICs (Trinamic et al.) and FPGA. Today, FoC can be done in (mostly) software with MCUs.

Fast feedback loops are also necessary in SMPS, another area where precision, low latency MCU peripherals and software are actively displacing traditional approaches.

But even if you update your PWM signal on every PWM cycle, you won't go much beyond 30kHz. At some point you're running into high switching losses on your MOSFETs.

There are solutions to those worries.... https://epc-co.com/epc/products/gan-fets-and-ics/epc23102

I didn’t know that. Thanks for letting me… meet the FOCers

I’ll see myself out of the Internet now.

The closed loop experiences a phase margin loss that is exponential with the frequency. At lower frecuencies it is negligible, but if you get close to the frequency of the delay the phase margin reduction becomes dramatic and the control goes from stable to unstable very fast.

If the sensor has a limited bandwidth, you add the conversion delay and then the computation delay on top of that you end up with a max workable loop bandwidth in the low tens of kHz and anything higher will have overshoots, oscillations, etc.

You see this in low cost products like MKS SERVO42x, where they're doing FoC with a GD32 MCU. It works; the motor runs cool, smooth and quiet, but the system is limited to 3000 RPM, and struggles with rapid acceleration because the control loop is too slow.

I have tried one. It has no torque. For what looks like an awesome product, it does not have the power to drive a peristaltic pump. I used the same motor on a TMC stepper controller and it's completely silent and works. It's open loop, so comparing apples to oranges but I am not sure what the MKS servo driver on a motor could actually do, aside from spin unloaded.

These can deliver 2.5-3A/phase, which should ample for a pump. Respectfully, I wonder what motor was involved and whether the current was configured: they come out of the box with conservative configuration so people don't burn up motors.

Nema 17

This is exactly correct. Low 10s of kHz is quite functional for machines moving in human space / speed.

If one is trying to do some assembly line (max # of operations per second), the power requirements alone get hard to manage. And then you're managing back EMF, eddy currents, heck, air resistance!

My rule: have dedicated low-level hw provide smooth PID response, mostly on the P term; and have a higher-level control produce the setpoint. Faster response means less need to rely on I or D terms as much (just because delta-T is so relatively small).

I similarly don't know much about motor control or hardware in general, but would this maybe open up multiplexing options?

People will always find a reason to complain or pretend they are controlling rocket motor servos with their ESP32

The datasheet apparently doesn't say, but judging by their other products' listed 12 bit SAR ADC sampling rates (and assuming this one is similar to what appears to be their standard ADC ) the conversion time will be on the order of 10uS.

Looks like you need an external PHY. It can talk to the PHY with RGMII which uses 12 pins, which are muxed with GPIO8-19.

The credit card tester bots go through the checkout process.

PoW wouldn't be a big issue for them though since their volume is much lower.

I would LOVE to be able to use rate limits (well actually, since I'm dealing with fraud not scraping, I'd ban the IP).

I can't, because every request comes from a new IP!!!

Well I administer an ecommerce site, and for the checkout page I block everything besides Canada and USA.

Because those are the only two countries that we've ever in the life of our business, had a legitimate order from.

It prevents the majority of credit card testing, but it is tempting to apply it to the whole site to reduce traffic and server load.

Is be seriously pissed off if I invested the time to build a shopping cart and got to the order screen just to be turned away. I hope that you have a clear message somewhere that you do not ship outside the US and Canada.

Yes it only allows US as the shipping address, and only US/Canada as billing address. The only reason we even allow Canada billing is because some of my relatives (Canadian) will order it and have it shipped to a parcel service on the US side of the border.

If the bad guys also had to pay $50/month/IP it would probably work.

The bad guys don't pay that much. And sometimes the bad guys actually use the IPs of other people (botnets on residential IPs) and don't pay anything at all.

They pay something. You can get a few ten cents per gigabyte for a voluntary proxy right now. I've never tried it long enough to get a minimum payout, so could be a scam for all I know (or maybe the minimum payout is the scam).

What would stop you offering someone a few tens of cents per GB to borrow any other token barrier you put up?

Maybe a plain WordPress install. Run something like WooCommerce and install a bunch of plugins to get the functionality that WordPress and WooCommerce should have built-in, and suddenly a cheap VPS can only handle 2 or 3 requests per second.

It's phenomenal how inefficient the WordPress/WooCommerce stack is.

Though the main issue I'm seeing is credit card testing, not scraping.

And I'm ideologically opposed to using a CDN (because it shouldn't be needed for such a small site!) so it's somewhat a self-inflicted problem...

"Security" plugins are also HUGE problem here, most of them turns "few cached DB SELECTs" (or static file read if you use caching plugin) into now a bunch of inserts, just to log/analyze "offender" IP and maybe block it, in many cases turning "blocking offender" to be more costly that would be serving the page without the security plugin

I'm not understanding your example; as far as I know gypsum/gypsum drywall isn't toxic.

If you let your kid eat drywall compounds, and inhale drywall dust in the process, you’re not only missing my point, you’re proving it.

Just because it isn't toxic doesn't mean it is edible...? I would not allow my child to eat drywall, but neither do I consider drywall toxic. i.e. if they started chewing on some drywall, I wouldn't haul them to the E.R. in a panic.