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12 points · 9 hours ago

This explains why the MIT sound recreation from a video of a potato chip bag in a sound proof room used the Mary had a little lamb rhyme.

Original Poster12 points · 8 hours ago

That rhyme was used a lot for testing early sound recording devices

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3 points · 8 hours ago

Even cooler to know that. Any particular reason?

3 points · 1 day ago

There’s a book/website that shows a buck of mechanisms :

Many of the mechanisms illustrated were created to solve some sort of domain problem.

You can download a program called “Linkage” if you want to play around with designing such mechanisms.

778 points · 2 days ago

This stuff is basically the only part of waste that goes to landfills. At least in sweden where we have a similar system. The hazardous waste gets mixed into a clay/slurry type deal, and then baked into bricks that then get buried somewhere far away from freshwater tables (i think this is the english word for it, fresh ground water)

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434 points · 2 days ago

freshwater tables (i think this is the english word for it, fresh ground water)

100% right!

5 points · 2 days ago

You can always pick up an automation direct PLC and use their free software & video training course for roughly the same effect.

I wouldn't get stuck being the "PLC guy" - you can always use PLCs in your designs, but don't get stuck doing just that.


I can't seem to find anything. Looks like 14.4V is a common tool battery, but there are no specs on the discharge rating.

This is for an ultralight - trying to avoid LiPo/LIon because fire = bad.



The fact that a 60C battery bulged mean you need alot of current. The battery was rated for 60*2.5A = 150A and it still bulged. Li-ion batteries are also NOT one-on-one replacements for Lead Acid batteries.


Is the battery being charged mid-air or do you take it home and then charge it?

Due to the weight limitations and current draw the best would be from best to worst:

  1. Supercapacitors, lots of current, not a lot of energy total, discharge over time
  2. Manganese based li-ion cells, the dangerous type, safe(er) if not pouch cell.
  3. LFP-cells, safer, less current so need more capacity
  4. NiMH
  5. Lead-acid
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Original Poster1 point · 2 days ago

I think it was just stored at near full charge in a 110F garage. Charging is done on the ground.

The NiMH has a 40A fuse, think it will blow when used on your engine.You should have a look at: "16V supercapacitor banks".

  • The energy-density is lower
  • The current capabilities are enormous
  • So you need less total energy stored
  • You need to charge them before a flight.
  • They discharge by themselves in a couple of days.
  • Charging current is also enormous.

To be safe you could stop using lipo's or increase it's capacity. More capacity means less stress on the battery under the same load. You could take these batteries and place two in parallel like this to increase the capacity. With these lipo's you could have a current draw of 90*5A = 450A. Two in parallel would give you 90*10A = 900A. Hobyking is known to lie about its ratings so lets take 33% of 900A = 300A. That would be sufficient.

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Original Poster1 point · 2 days ago

Okay so - I looked up the start motor and it is rated as 12V/250W. So that's ~20A. The motor just needs to crank for a few seconds so accounting for inrush current, etc, it looks like I need something around ~60A. (I'm guessing the fuse is a slowblow type).

I guess I don't understand how their 3000mAh battery pack manages to crank the motor.

Anyway - I'm still very reticent about using LIPOs, even if they are used far below their rated rates.

The SLA battery is pretty heavy (~6lbs) so quite undesirable.

LFP batteries look interesting, but they seem quite expensive. Something [like this]( looks like it'd be perfect, but $150! Might as well the paramotor rated battery :)

Any other suggestions?

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Original Poster8 points · 5 days ago

You've got a good point here. They're just SO loud, it makes you think they're the norm.

I'm wondering why the community hasn't shunned people like this? We shun people all the time in BASE. BASE operates in uncertain legal areas sometimes so we've got to protect our sites just like people are passionate about protecting the ultralight "no license required" status. We spread the word and those people are no longer welcome to participate in events or jump with the majority of the community.

But on a positive note, I'm really liking what i'm seeing from on the electric side of this sport! Same with electric cars, we just need the battery tech to get a liiiiitle better. My next motor will be electric.

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3 points · 3 days ago

The thing about paramotors is that you can literally fly from anywhere. I live in a metro area of about 3Million people, but are only ~350 people in the local paramotoring group on facebook (this includes visiting pilots).

You can spend your entire life flying every single day and not encounter another another paramotoring pilot.

3 points · 3 days ago

Are we sure the guy doesn't actually know how to fly? He seemed unusually competent (minus ear protection) for someone who's never flown before. I can imagine someone hamming it up for youtube views.

2 points · 26 days ago

You would need an exemption from the FAA because that breaks 103 rules. If it were me I'd probably start here:

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1 point · 3 days ago

The FAA is people too.

Also, FAR105 (Sport Parachuting) has similar prohibitions on doing jumps over congested areas or assemblies of persons, but they have form 7711-2 which you can submit to request such permission. Doesn't seem to apply to FAR103, but I'm sure they would review it at least. If your engine is shut off aren't you almost parachuting anyway?

1 point · 3 days ago · edited 3 days ago

The tongue weight is not a rating for how strong the hitch is, it's a rating for how well your car will maintain control when there is a load applied to the rear of the vehicle.

If you exceed the tongue weight, you are unloading the front wheels of your vehicle past the tested condition and your steering becomes less effective.

Essentially -- your rear wheels are a fulcrum. The car body + hitch are the lever.

This is the reason why heavier cars have a higher tongue rating - their suspension is rated to take a heavier load and they also have more weight so that it takes a higher weight push on the lever to unload the front wheels.

Is that canon?

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65 points · 4 days ago


3 points · 4 days ago

Oh. In english units when they talk about force they mean the force exerted due to gravity by an object weighing that much.

So - you can use a fish scale. If you lack a fish scale, you can use a piece of string, a pulley, and a hanging 10 lb weight. Like this

Original Poster1 point · 4 days ago

So the trigger pull scale will work the same way too? I already have one of those

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2 points · 4 days ago


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5 points · 5 days ago

You're missing the point of cross fit though: flail around wildly in an effort to injure yourself in the short term and long term. This exercise accomplishes both.

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1 point · 5 days ago

Seriously - I do bouldering at a gym that also does CrossFit. The CrossFit area has giant banners advertising local medical/physical therapy services so that you can get back into CrossFit after you get hurt.

Like.... what?

1 point · 6 days ago

I'd previously quit one job where I was working on a project for a few years and then .... was back in six months since I kept thinking about how that project never got finished.

2 points · 6 days ago

Haha - either buy it now or buy it later with concealed flood damage ;)?

I think it's an attempt to lock the sheet bend in location so it doesn't slip when it's not under load. I noticed this variant when fooling around with nets a few months ago.

I have since learned that you can hit each knot with a soldering iron, and slightly melt the line to tack it in place if you are sewing a net with synthetic.

Also, making a net may be fun, but it's a waste of time unless you just want to learn the skill. You can buy netting scraps or even cut up a cheap mesh hammock for your own projects.

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Original Poster1 point · 6 days ago

I need to actually mend a net on my Paramotor 😆

5 points · 8 days ago

The electric car industry seems to be in a bit of a flux right now?

8 points · 8 days ago

Why do you say this? Because Tesla is in the news and the stock is yoyoing? I think as an industry there is a huge industry commitment to growth and a ton of startups in the ev space both in the u.s. and China...

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1 point · 7 days ago

Because if Tesla craps out there is going to be a glut of very experienced EV engineers looking for work. Good luck competing with them.

2 points · 7 days ago

I’ve been reading Cadillac Desert lately and the claims it makes about the misuse of water in the West are eyebrow raising. Ie: there’s plenty of water in the rivers to irrigate and feed millions of people, but due to how the water rights were divided, lots of the water ends up going to arid, high-elevation farming states where only low value crops can be grown.

I thought Snape was mostly being horrible to Harry as to not rouse suspicions. I feel like if he gave Harry special treatment or was even polite or civil towards him, at least Malfoy would have found out and told his parents, etc. Plus, he was extremely bullied by Harry's dad when he was younger and I assume that resentment might still last especially when you're seeing someone that looks so much like your tormentor but he never outright hurt Harry (I don't think giving him detentions and stuff counts lol).

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6 points · 8 days ago

But there was no hint of Voldermort until the end of the first book. As far as everyone knew, he was gone..

4 points · 8 days ago

Look into the curta computer. There are 3D CAD files available

5 points · 9 days ago

Why do you need version 0.21.0?

Latest is 1.1.3

Original Poster2 points · 9 days ago · edited 9 days ago

I did n0t know there is a newer version.

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7 points · 9 days ago

Ah ok.

So put pg 1.1.3 in your Gemfile. Also, if you don't specify any specific version, then bundlr will try to find the version that will most likely work for you (not guaranteed) by looking at what you have available in your environment and any sort of other dependencies between other gems.

It's generally good practice to lock in a specific version of your gems for production purpose since a newer version of a gem could change the API interface or somehow break your application.

The downside of locking your gems down to a very specific version is that you may miss out on bug fixes or new features. So - in the future if you run into what you feel is a bug with a specific gem, you can always try updating it manually to the most recent version.

You definitely don't need to purchase your glasses from an optometrist, but don't skimp on visiting your eye doctor for health. I am an OD student and have seen way too many patients with conditions that will eventually blind them because they skimp on getting proper eye care or use websites that just give them a prescription.

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3 points · 15 days ago

Yeah but you can't do an eye exam online. The only thing that any of the online places do is take your prescription and make glasses - which is not any different than a brick & mortar eye glass place.

There are many websites that are marketing online eye exams (and even some stores that are implementing kiosks. This will get your prescription and then some doctor will bulk sign off on all the prescriptions. This is something fairly new that will eventually get banned, but is around right now. In my case, 25% of what I do with patients involves the prescription. This part is easy and can be done in 5 minutes. The other 75% involves health of the front of the eye (think corneal health), the inside of the eye (think lens), the back of the eye (think retina), and the neural connection between your eye/brain. So while I am all for great deals on glasses, since I use Zenni myself (especially since I have seen the markup on glasses), I would be wary on skipping proper care.

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1 point · 9 days ago

Right - I'm not saying don't go to an eye doctor - I personally go out of my way to get my eye exams done at a place that does cataract, etc, surgeries in the belief that the doctors there deal with complex eye-related issues and so can recognize them better.

However- I don't see places like Lenscrafters offering me any sort of value. The salesperson takes a brief PD reading and then takes my prescription and order from me and... I come back in a few hours to pick up my new frames. What do they do that Zenni doesn't?

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3 points · 9 days ago

Hmmm two posts about babysitting.

Talk about Astro turfing.

4 points · 9 days ago

Hmmm two posts about babysitting.

Talk about Astro turfing.

2 points · 10 days ago

How about using something like this?

It's hard to know what tolerances you need without knowing more about your application.

sdn commented on
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2 points · 12 days ago


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