Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Some simple measurements using that Pololu driver in its default mixed decay mode and that Arduino sync generator. The captions give the operating conditions; basically, I’m varying the rotation speed by cranking the signal generator driving the Pololu board.
At 1 rev/s, it’s about as good as it gets:
Back EMF – 9V 400mA 1 RPS
At 5 rev/s, the driver has trouble getting current out of the winding:
Back EMF – 9V 400mA 5 RPS
At 10 rev/s, things are getting ugly:
Back EMF – 9V 400mA 10 RPS
At 20 rev/s, the back EMF has pretty much taken control of the current and the driver is going along for the ride:
Back EMF – 9V 400mA 20 RPS
At 25 rev/s, the driver produces only occasional dents in the waveform:
Back EMF – 9V 400mA 25 RPS
At 25.3 rev/s, the motor stalled. Even with no back EMF (what with the rotor being stopped and buzzing in frustration), the driver can’t force the current to behave:
Back EMF – 9V 400mA 25.3 RPS
I don’t have any way to measure the motor’s output torque, but at 1500 RPM there won’t be any worth mentioning.
For what it’s worth, 25 rev/s means the driver is handling 40 k steps/sec = 25 µs/step. The motors in a Thing-O-Matic run at 3 rev/s to move the XY stages at 100 mm/s, so scale what you see here accordingly.
Strictly speaking, I do not have a beard: I simply do not shave (*). There being no money in selling Trimmers for the Non-shaving, a while back I bought a battery operated Beard Trimmer. The NiCd cells lasted for the predictable few years and recently gave up the ghost entirely: an overnight charged produced a weak buzz with no cutting action to speak of.
The case uses one-time snap-together latches, which makes dismantling it a challenge. Start by removing all the gimcrackery on the business end, then pry out the two latches holding the it-was-white-once cutting length adjustment ring. With that out of the way, undo the two latches inside the top and work your way down, prying the case halves apart in the way the overlap flange doesn’t like, so as to force the latches loose.
This picture shows the six latches, three on each side. The ones just to the right of the blue impeller require the most cursing:
Beard trimmer case and innards
The circuit board snaps out, with the two PCB contact areas clamped down by springy contacts leading to the motor.
Beard trimmer – battery charger PCB
The two NiCd cells boast of their High Energy, but they’re only 600 mAh. That’s actually too much for this high-drain, short-run application, as they don’t completely discharge. They’re held in place on the right end with a blob of hot melt glue:
Beard trimmer – NiCd cells
I unsoldered the cells and gave ’em a brute-force overnight charge at C/10 = 60 mA, then ran a discharge test (clicky for more dots):
Beard Trimmer – NiCd Discharge Test
Lookee that! The cells still deliver their rated capacity, even though they no longer worked with the stock charger. I repeated the slow-charge and discharge trick, which produced a perfectly overlapping trace.
Flushed with success, I unleashed the built-in charger overnight, then produced a third overlapping trace.
So they suffered from voltage depression, most likely due to never being completely discharged and then being overcharged far too often. That’s cured by a complete discharge and recharge, which worked perfectly.
I hack back the overgrowth when it gets bushy and recharge the trimmer when it seems to be getting weak, which used to take a week or two. That’s a bad way to maintain a NiCd battery, particularly as the PCB applies a very low load to keep its computronium running, but I have better things to do than babysit a beard trimmer. Honest.
Anyhow, assembly is in the reverse order and it’s perfectly happy again.
I probably won’t change my evil ways, so the next time I’m sure the battery will be really and truly dead.
(*) Not shaving adds about ten minutes a day to my life, which I regard as a fair tradeoff over the course of several decades. It also added a decade to my apparent age, Back In The Day when that mattered. Now it seems to knock off a decade, which isn’t entirely a Bad Thing.
Saw this at breakfast early one morning in DC on our April vacation:
Panera Bread alarm panel – bad clock
Here’s the key part, amped up for readability:
Panera Bread alarm panel – clock detail
I’m sure the manager’s three-ring binder has a whole section about the alarm system, its care & feeding, and the importance thereof. I’d guess there’s a dead battery in there somewhere and a power failure in the recent past.
This ooops obviously doesn’t matter, right up to the point where they have a break-in and the alarm system timestamps the event incorrectly.
The camera peered through a pair of window panes across the entranceway, as I didn’t want to get too conspicuous… we were, after all, in DC.
It has nothing to do with the load o’ tools in the left underseat bag on my Tour Easy. It has everything to do with the fact that we ride on the shoulder of crowned roads.
Faired Tour Easy on crowned road
Here’s a cross-section of one defunct Schwalbe Marathon rear tire with the tread obviously thicker on the left side, which would be the right side of the mounted tire:
The base of that case makes a good protector to keep an Arduino board out of the conductive clutter on a typical electronics bench. I stopped the printer shortly after it finished the bosses atop the mounting posts:
Our Craftsman lawn mower has both a deadman grip for the motor (the Operator Presence Control Bar) and a Drive Control Lever that engages the rear wheel drive. The latter requires a death grip to keep the belt engaged, which means you (well, I) spend about two hours clenching the grip.
Lawn mower – compound leverage handle
I’ve long since flipped the control to the left side and added thick foam padding, but there’s no adjustment that reduces the death-grip requirement: you can change the engagement distance, not the spring constant.
Evidently the Sears engineers have much stronger hands than anyone in our family.
The doodad hose-clamped to the upright part of the mower handle is a basically a hinge that applies force to the tip of the red handle. The hinge axis lies far enough from the handle’s pivot so that holding the hinge against the handle requires very little force; at least it’s no longer a death grip.
Lawn mower – compound leverage handle engaged
It’s not an ideal solution, but it engages and (more importantly) disengages easily. I still don’t like mowing the lawn, but at least I don’t return with a crippled-up hand.
The hinge is actually a lock hasp, so it has a slot that slides neatly over the Drive Control Lever’s tab. I beat both sides into a more-or-less cylindrical form over a piece of pipe, while miraculously not bending the hinge pin.
Evidently the Sears engineers never actually used the damn mower for two hours at a time.
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness. That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness. Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes; and accordingly all experience hath shewn, that mankind are more disposed to suffer, while evils are sufferable, than to right themselves by abolishing the forms to which they are accustomed. But when a long train of abuses and usurpations, pursuing invariably the same Object evinces a design to reduce them under absolute Despotism, it is their right, it is their duty, to throw off such Government, and to provide new Guards for their future security.
We read the original document in DC a few months ago, while doing the touristy thing. These days, that means submitting to a search on the way into each museum; Mary lost her forgotten-in-the-bottom-of-her-purse Swiss Army Knife to the Smithsonian guards.
We left town feeling that something has gone badly wrong in the last decade or so.
The Smell of Molten Projects in the Morning 