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Joined 3 years ago
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Cake day: June 7th, 2023

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  • Ah good, we can talk physics.

    Newton’s Second Law

    Okay, let’s start with Newton’s second law:

    F=m*a

    but we’re going to flip it around to

    a=F/m

    so that acceleration of a body is equal to the force acting on that body divided by its mass. What this tells us is that for a given force f applied to a vehicle of mass m, the vehicle will accelerate at rate a.

    Where does that force F come from? From the tires acting against the pavement per the lever arm equation:

    t=F*d

    or, a force F working through a lever arm of length d will produce a torque t, but again, we’re going to flip it around a bit to give us

    F=t/d

    Which tells us that a given torque t operating through wheels of radius d will produce a force on the pavement of F.

    Now we’re going to combine the two to give us

    a=t/(d*m)

    So, acceleration is directly proportional to the applied torque and inversely proportional to mass which absolutely supports what you are saying at first glance.

    HMI

    HMI is an acronym for Human Machine Interface which is a whole mechanical design field built around helping humans interact with complex machines like cars. Now I have to admit some ignorance here, but I don’t know what type of vehicle you drive so I’ll start simple.

    In my vehicles, both gas and electric, there’s two pedals specifically related to acceleration. The accelerator (sometimes called a throttle) and the brake pedal - and these pedals are remarkable devices.

    The accelerator (negating regenerative braking that we’ll touch on later) controls positive acceleration while the brake controls negative acceleration. Basically, the accelerator makes us go faster (forward or back) and the brake slows us down. But here’s where it gets nuts - these are proportionate input controls. It isn’t like a light switch rather, it’s more like a dimmer - the more you press on the pedal, the more acceleration you get. The way this is accomplished is by controlling the torque applied by the motor. This is key - we can control the torque output of the motor.

    Puting it all together

    You are absolutely correct that the electric motors in EVs can generate absurd torque which, as we’ve seen, results in incredible acceleration. I certainly had some fun when my EV was new. But, 99% of the time, I’m driving in traffic or on the highway and my accelerator inputs are very light - the motor is generating only a small amount of torque it’s capable of producing.

    Gas cars operate in a similar, albeit wildly more complex manner (the accelerator pedal controls the amount of air getting into the engine, then a feed forward control mechanism is guessing how much fuel is needed and a feedback system monitors for the presence of unconsumed oxygen or uncombusted fuel in the exhaust). The important thing is that both are capable of delivering variable torque based on operator inputs.

    So let’s imagine we have two cars stopped side by side at a stoplight that turns green. Both vehicles can use their accelerator pedals to control their rate of acceleration and they both accelerate away in a nice sedate manner.

    As I mentioned in a previous post, an Ioniq 5 (EV) weighs about 2000kg while a Rav4 (gas) weighs about 1700kg. The EV therefore weighs roughly 15% more. If both vehicles leave the line at the same rate of acceleration the torque output from the EV will need to be 15% higher.

    a=t/(d*m)

    That then takes us back to Newton’s Second Law and thus the longitudinal interaction force between the tire and pavement will be about 15% higher - which is not nothing, but let’s add some context.

    Perspective

    The coefficient of drag Cd for the Ioniq 5 is 0.288 vs 0.310 for the Rav4 - about 8% higher. The drag equation is

    Fd = 1/2 r * u^2 * Cd*A

    where r is the air density, u is velocity, and A is the reference area. In this case r and A are equal (well, mostly equal in the case of area) for our ICE and EV examples.

    What this equation tells us is that at a given speed, the Rav4 requires 8% more driving force to overcome wind resistance. This isn’t just during the acceleration phase, but at all times.

    It also shows us that drag forces go up with the square of speed. That means that if you increase your speed from 100 to 115km/h (15% increase), the drag forces go up by 32%.

    So if we compare the EV to the ICE vehicle under cruising conditions, the friction forces between the tire and the pavement are HIGHER for the ICE vehicle in this example.

    Even more than that, the impact of increasing speed dwarfs both the impact of mass and the impact of the coefficient of drag.

    Summary

    I haven’t come across a peer reviewed body of knowledge that compellingly argues that an EV and an ICE vehicle, driven similarly, will have substantially different rates of tire wear. Rather, speed, proper inflation, and road surface seem to be much more significant. The bulk of reports of accelerated tire wear come from journalists and influencers reviewing vehicles - groups who likely enjoy the acceleration that EVs are capable of, but don’t have to use.


  • The tire thing is FUD in my experience - and I haven’t seen anything other than anecdotal evedince that under similar driving patterns and styles there’s substantial differences in wear. My Ioniq 5 for example only weighs ~15% more than a Rav4 and less than a Honda Pilot.

    When I drove a Subaru STi, I shredded my first set of tires. My station wagon, that weighed more, the tires lasted forever because I drove like an old man. With EVs, if you have fun enjoying that instant torque by punching it off every stoplight, you’ll definitely shred some tires. Accelerate smoothly and I don’t see why tires would see substantially shorter lifespan - which is what I’m seeing from my personal tread wear so far (but that’s anecdotal and therefore of extremely limited value).





  • Hmm, depreciation on my Ioniq isn’t anything like that bad. And I had a fuel injector quit in my last car at 130k. The cost of replacing all four injectors was a heck of a lot more than quoted. I intentionally lowballed service costs for ICE vehicles because people tend to (dramatically) underestimate what they spend on maintenance.

    Also, the tire thing is FUD. Tire wear is higher IF you regularly use all that torque. If you floor it off every light (which is very fun) you shred your tires. If you drive conservatively there’s minimal difference. My Ioniq 5 weighs about 2000kg, a non-plug-in Rav4 hybrid weighs 1700kg, and a Honda Pilot is around 2200kg so the weight just isn’t that different from other vehicles.







  • animatedknots.com - amazing step by step on how to properly tie things. The downside is that there are a lot of knots that are either hyper specific or more decorative than anything. I climb and sail - both are knot-heavy. 95%of the time I use one of five or six knots/hitches. I’d focus on the utilitarian knots personally. These are the knots that can accomplish real stuff - but if you get them wrong, could be fatal in the wrong circumstances.

    • Simple overhand - great for keeping a loose end from flopping around, connecting two ropes (need long tails or a secondary knot to keep it from moving), or joining webbing (known as a water knot in this context)
    • bowline - great for tying around things like if you want to anchor something to a tree
    • figure 8 - the go-to for tying yourself into a rope when climbing. I rarely use it anywhere else as it’s bulky and difficult to untie if loaded hard. A bowline can be used in its place for tying in, but the big advantage of the 8 is that it’s easy to visually check. Every few years a miss-tied bowline kills a climber.
    • clove hitch - this one is super underrated. It looks like you just wrapped a rope around something but it self tightens thanks to the way the strands lie over each other. It’s also super easy to adjust.
    • trucker hitch - it’s really just a couple of overhand knots, but this one is my default for lashing down loads because you can get the rope super tight. This is how I tie my canoe down to the roof of the car.
    • fisherman knots - killer for connecting ropes - or making non-load-bearing adjustable loops (bracelets, necklaces), or tidying up loose ends.

    Bonus knots *alpine butterfly - gives you a load bearing loop in the middle of a rope without requiring access to the ends. An overhand on a bight also gives a loop, but the overhand can move when loaded. Alpine butterfly stays where you put it, looks cool, and is fun and easy to tie. *prussic - this hitch can slide along a rope when unloaded and then locks when you apply weight. This let’s you move up or down a fixed line. A Texas Prussic involves one prussic attached to your harness and one free but with a foot loop. Hang on the harness prussic, slide the unloaded foot one up the rope. Stand up on the foot one (locks in place) and slide the unweighted harness loop up the rope, sit back down in your harness. Congrats, you just ascended 100mm up a rope. Rinse and repeat until you get to the top or reverse the process to go back down.




  • potate@lemmy.caOPtoAlberta@lemmy.caSolar and EVs
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    19 days ago

    If you live in Calgary, the city has a fantastic funding program. The city puts up the money and then you repay it as a top up on your property taxes with a minimal interest rate.

    The payback period of solar is generally shorter than the payback period of the loan from the city so it’s likely you would see your monthly cash flow improve right off the hop.

    There are other communities in Alberta offering similar programs. I’m a giant nerd about this stuff so feel free to DM me.