Wikipedia:Reference desk/Archives/Science/2019 February 25

= February 25 =

Are there any doctors ...

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Are there any doctors in the US which perform a bilateral epididymectomy for birth control? Futurist110 (talk) 21:22, 25 February 2019 (UTC)


 * This better not be a just Google it question. 67.175.224.138 (talk) 01:42, 26 February 2019 (UTC).
 * This general topic seems to be of great interest to the OP. One would think that Google could provide some answers. Although he could just start by asking his own urologist. ←Baseball Bugs What's up, Doc? carrots→ 04:04, 26 February 2019 (UTC)
 * He's been asking questions about various testicular surgeries for over a a year now. At this point, we should simply give the boiler plate "visit a doctor and ask them directly". These questions are growing tiresome, and it's clear he's looking for personal medical advice.  Stop asking here, and talk to a physician.  If you can't find a specialist, start with a general practitioner and get a referral.-- Jayron 32 04:43, 26 February 2019 (UTC)

Anatomy of rental electric scooters
Those new dockless electric scooters for rent (from Bird, Lime and so on) seem to have the battery inside the frontal vertical bar. At least these feel quite heavy. Wouldn't it be a more stable design to put the battery in the horizontal base, where the user stands? Doroletho (talk) 23:46, 25 February 2019 (UTC)
 * Maybe, maybe not. How do they get recharged? That could figure into the design. ←Baseball Bugs What's up, Doc? carrots→ 04:03, 26 February 2019 (UTC)


 * How are you measuring 'stability'? Although putting the centre of gravity as low as possible (i.e. stand on the battery) seems like a good idea, in practice experience with bicycles (such as touring bikes with heavy panniers) favours putting the weight forwards, even if that means going higher. Pendulum stability with a low CoG just isn't an issue for bikes - after all, the human (and heavy) rider is at the highest point. What matters more is the forward-backward location of the CoG. Under braking (and bikes don't accelerate or corner as hard as they can brake), a forward CoG is stable, but a rearward one can be an unwelcome surprise to the rider.
 * There's also the question of familiarity. Many of these rental bikes and scooters have to cope with riders who are unfamiliar with them. In that case, it's easier to add any additional mass as close as possible to the rider's body. Non-riders are used to their own mass, or even carrying an additional mass, but not riding a vehicle where an additional mass is attached to the far end of a lever. This may not be the best place for that mass, but it's the easiest place to learn how to deal with. Andy Dingley (talk) 20:35, 26 February 2019 (UTC)


 * Two-wheeled vehicles (other than the suspended monorail) always have their centre of mass above their pivot point. This means that pendulum stability does not apply. Statically, they behave like an inverted pendulum, which is unstable.
 * Instability isn't necessarily bad. When deviations from equilibrium grow on a timescale of more than a few seconds, the rider has enough time to compensate. For a point mass (i.e., the battery is small compared to its distance from the ground), moving the mass up will increase this timescale, making the vehicle easier to control. Furthermore, too much stability makes it hard to manoeuvre.
 * Also keep in mind that two-wheeled vehicles aren't static. We have to talk about the dynamics and Wikipedia has a nice article about bicycle and motorcycle dynamics. At high speed, the gyroscopic effect of the front wheel makes a bicycle too stiff to remain stable and it will fall over in capsize mode, similar to an inverted pendulum, but the deviation from equilibrium only increases on a timescale of 100 seconds or so, making this instability unnoticeable (Meijaard et al., Proc. Royal Society A, 2007).
 * Or are you talking about Segway-like scooters? I've never seen one. When mounted they are always unstable, but moving the centre of mass up will increase the timescale on which they fall over, making it easier to compensate. PiusImpavidus (talk) 11:02, 27 February 2019 (UTC)
 * Segways keep the battery low and close to the axle - as do 'hoverboards'. Their control systems can react fast enough, but this reduces their moment of inertia and the torques needed. For the comfort of the rider, they need to keep the rider's mass further away than the machine, otherwise the motors would need more torque and the riders would be thrown back and forth more.
 * For the hoverboards, the limit isn't the motor torque, but the current supply to these motors. It's greater than their (fairly small) battery packs can deliver, so they have to use supercapacitors as a reservoir capacitor in the motor drives, just to cover the peak surges for balancing it over a bump. Andy Dingley (talk) 11:23, 27 February 2019 (UTC)


 * For clarity, the OP is referring to this sort of thing Bird Scooters 1 2018-09-28.jpg [//www.youtube.com/watch?v=YsVLiFCHWO0], covered in our Electric kick scooters and Scooter-sharing system articles. Some of the non rental versions do have the battery in the base [//www.youtube.com/watch?v=qChbzq_Vso8]. Nil Einne (talk) 13:09, 27 February 2019 (UTC)
 * According to [//qz.com/1257198/xiaomi-makes-the-bird-and-spin-scooters-taking-over-san-francisco/], at least some of the Bird scooters are simply rebranded Xiaomi M365. Well they obviously have their own electronics or at least firmwae for the rental part, but I presume the main battery etc are in the same place. Lime seem to use slightly more customised products, at least the ones I've seen (but also per that article). Considering that it took them a while to figure out that suddenly applying a high level (maximum?) of breaking for no reason while at high speed is probably a bad idea [//www.stuff.co.nz/business/110815450/lime-disappointed-with-auckland-council-escooter-ban-calls-for-level-playing-field] [//www.theverge.com/2019/2/25/18240489/lime-sudden-excessive-braking-firmware-bug-scooter], and I think they still haven't figured out that they should at least confirm they've updated the firmware on their scooters to stop such things before starting a mass email campaign [//www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=12206602] [//www.nzherald.co.nz/business/news/article.cfm?c_id=3&objectid=12206910], who knows if their design choices made any sense. Nil Einne (talk) 13:40, 27 February 2019 (UTC)
 * Mind you, on the firmware side at lest I'm not sure if the Xiaomi M365 gives much reassurance it's better [//www.wired.com/story/xiaomi-scooter-hack/] [//blog.zimperium.com/dont-give-me-a-brake-xiaomi-scooter-hack-enables-dangerous-accelerations-and-stops-for-unsuspecting-riders/]. Nil Einne (talk) 13:49, 27 February 2019 (UTC)


 * This article was one of the first things to come up when I typed the statement "Battery on Bird Scooter" into Google. It seems to answer many of the questions and issues brought up in this thread.  -- Jayron 32 13:23, 27 February 2019 (UTC)