7 ms·

why do steer by wire at all? Is it cheaper somehow?

by whelp_24 3y ago

m463 3y ago
Hmmm.. I would guess decoupling would allow variable ratio steering based on speed or preferences.
- lttlrck 3y ago
  Electric power assist already allows that. It's probably cheaper, lighter and maybe safer to have no steering column.
  - m463 3y ago
    I meant decoupled variable ratio, not mechanical variable ratio[1], not power assist. sort of like turning mouse acceleration on and off. [1] https://en.wikipedia.org/wiki/Steering_ratio#Variable-ratio_steering https://en.wikipedia.org/wiki/Steering_ratio#Variable-ratio_...
  - yreg 3y ago
    No matter what we think about FSD, Tesla's end goal are robotaxis – eventually probably with no steering wheels. Steer by wire is a stepping stone in that direction.
  - giobox 3y ago
    They almost always only vary the amount of power assistance, not the ratio. The ratio is fixed on virtually all electrically power assisted steering racks ever shipped. There is still a fixed mechanical linkage - decoupling this is what allows the ratio to be dynamically adjusted. To date only a handful of Lexus production cars have had dynamic variable ratio and decoupled steering via drive by wire. Electric power steering is essentially the same in use as traditional hydraulic systems - they just replace the hydraulic assistance with electric motors. The big advantage of decoupling and steer by wire is dynamic variable ratio, as well as packaging - no steering column to worry about making space for.
    - inferiorhuman 3y ago
      Nah, there are variable ratio mechanical systems. On a rack and pinion setup, for instance, you vary the spacing of the teeth on the rack. ZF's been doing this for decades.
      - giobox 3y ago
        Generally speaking almost all mechanical steering systems are not dynamic though, you are missing the point entirely. It can't change the spacing of the teeth on the fly - steer by wire effectively does. The number of turns lock to lock on a mechanical system is almost always the same, regardless of speed. With steer by wire, you can easily implement say one turn lock to lock at low speed for easier parking, increasing to 2-3 turns at highway speeds for stability. Which is essentially exactly what the recent Lexus model with such a system does. At low speed it can turn its wheels from one extreme to the other in just 150 degrees of steering wheel rotation - no hand over hand turning etc. 150 degrees is essentially unthinkable on a mechanical rack and pinion system, as it would make the car incredibly twitchy on a highway. > https://www.motortrend.com/reviews/2023-lexus-rz450e-steer-by-wire-yoke-review/ https://www.motortrend.com/reviews/2023-lexus-rz450e-steer-b...
        inferiorhuman 3y ago
        It can't change the spacing of the teeth on the fly. Geez, Elon really ought to start a goalpost moving company. But hey I'll play: yes, yes it can. That's precisely what BMW's active steering is, yes it's mechanical, yes it varies the ratio depending on speed, and yes it's been around for a couple decades now.
        giobox 3y ago
        BMW active steer doesn't get remotely close to 150 degrees lock to lock when maneuvering (minimum rotation reached is ~720 degrees/2 turns), or offer the infinite and instant range of adjustability you can get with a drive by wire system. But sure, it's just the same. I couldn't care less whether the system is on a Tesla or not, its just abundantly clear there are some design and packaging advantages when you lose the mechanical link in anything with a steering wheel. The vast, vast majority of rack and pinion systems ever made, both old and modern, don't adjust number of turns lock to lock at all, whereas the ability to essentially infinitely adjust it is inherent in all drive by wire steering systems.
XorNot 3y ago
It means where you put the steering wheel doesn't have to have a firewall penetration and mechanical linkage through to the engines. That's a lot of mechanical joints which need to be continuous, and need greasing, sealing and have limits on relative angles between them that you don't need - as well as they have to have enough strength to transmit the forces involved. By contrast, with steer-by-wire your system is essentially a black box you bolt on somewhere and then a more compact set of motors which can be coupled to the wheels at whatever is mechanically optimal. The main reason not to do it is because your control systems need to be perfect. Conversely, above a certain vehicle mass, it's also not realistic to think that a human would be able to control the car anyway if the power steering failed, or that control system failures would still be devastating (i.e. if the power steering starts fighting you, you're going to lose).
- whelp_24 3y ago
  Big rigs used to not have power steering, i think with adrenaline you'll be able to steer. I do concede that the power steering fighting you would be bad
  - bravetraveler 3y ago
    I just want feedback from the road, wires don't give me that
    - kuhsaft 3y ago
      You can absolutely get feedback from steer-by-wire. Ask any racing sim enthusiast. Those racing sim wheels can provide enough feedback to rip the wheel out of your hands.
      - bravetraveler 3y ago
        That "feedback" doesn't meet my poorly framed hyperbole. I'm intimately familiar as a driver; both in sims and Real Fast Cars. At what point does it go from feedback to lies? Some computer saying "yep, this is what's happening", if you're lucky. I'll yield that has been the trend for eons. That said, I don't want more of it. What lead to my first comment is the understanding that Tesla doing something where it's... different wires. Bus vs Ethernet or whatever. It sounds even more muted/numb. I don't want a real car to feel like a sim. It's getting harder to tell the difference for the wrong reasons. It's not that the simulators are closing the gap, but that the cars are becoming simulators. Lowering standards is definitely one way to meet them. Take your "we have feedback at home" and keep it I'm half joking through most of this, by the way. The problem is there but I'm deliberately overstating it
bonestamp2 3y ago
It has rear wheel steering, so there would be a lot of linkage needed to do that mechanically. That said, GM has been doing rear wheel hydraulic steering for a couple decades and the front steering is still mechanical in those (at least historically, not sure if that has changed with their EV lineup).
- Grazester 3y ago
  Just about every car manufacture has done rear steer at some point I believe. Nissan had it done initially with a Hydraulic system then electric.
  - bonestamp2 3y ago
    Probably. I know Dodge and Mitsubishi have done it too.
giobox 3y ago
Allows you to vary the steering ratio dynamically (how many "turns" lock to lock). Means a lot less arm twiddling during lower speed maneuvers, and can gradually increase the ratio as speed increases. Traditional mechanically linked steering racks (electric or hydraulic) don't do this and are the same number of turns lock to lock regardless of speed - they can only dynamically vary the amount of power assist, not the ratio. It's been something car manufacturers have wanted to do for a while. Another benefit in theory is packaging - you can free up more space for cabin, front trunk or motors etc when you don't have to route a physical steering column.
- pandaman 3y ago
  BMW had this on mechanically linked system for 20 years. It's called "Active Steering" in their marketing speak.
  - deleted 3y ago
    [deleted]
  - giobox 3y ago
    It's not really the same at all in practice though. With steer by wire you can get the lock to lock literally as little as you like - 150 degrees at low speed lock to lock in the Lexus system for example. In theory it could go from one extreme to the other in a single degree, its just software, although obviously no one sane would implement this. Active Steering on BMWs doesn't get remotely close to 150 degree low speed lock to lock.
    - pandaman 3y ago
      It's a system that changes the ratio of the steering wheel rotation to the wheel angle dynamically while still mechanically linking the wheels to the steering wheel. It does not have the same parameters as Lexus system but many other things differ between BMWs and Lexuses too.
      - simondotau 3y ago
guidedlight 3y ago
Steer by wire is cheaper to produce, as it allows you to reduce costs for RHD markets (e.g. Australia, New Zealand, UK, Thailand, Indonesia, Japan, etc). For example, Ford F-150 and RAM 1500 trucks from the US are exported to Australia where they need to undergo an expensive conversion process before they can be sold. This is why a base model F-150 is US$74000 in Australia.

why do steer by wire at all? Is it cheaper somehow?

m463 3y ago

Hmmm.. I would guess decoupling would allow variable ratio steering based on speed or preferences.

lttlrck 3y ago
Electric power assist already allows that. It's probably cheaper, lighter and maybe safer to have no steering column.
- m463 3y ago
  I meant decoupled variable ratio, not mechanical variable ratio[1], not power assist. sort of like turning mouse acceleration on and off. [1] https://en.wikipedia.org/wiki/Steering_ratio#Variable-ratio_steering https://en.wikipedia.org/wiki/Steering_ratio#Variable-ratio_...
- yreg 3y ago
  No matter what we think about FSD, Tesla's end goal are robotaxis – eventually probably with no steering wheels. Steer by wire is a stepping stone in that direction.
- giobox 3y ago
  They almost always only vary the amount of power assistance, not the ratio. The ratio is fixed on virtually all electrically power assisted steering racks ever shipped. There is still a fixed mechanical linkage - decoupling this is what allows the ratio to be dynamically adjusted. To date only a handful of Lexus production cars have had dynamic variable ratio and decoupled steering via drive by wire. Electric power steering is essentially the same in use as traditional hydraulic systems - they just replace the hydraulic assistance with electric motors. The big advantage of decoupling and steer by wire is dynamic variable ratio, as well as packaging - no steering column to worry about making space for.
  - inferiorhuman 3y ago
    Nah, there are variable ratio mechanical systems. On a rack and pinion setup, for instance, you vary the spacing of the teeth on the rack. ZF's been doing this for decades.
    - giobox 3y ago
      Generally speaking almost all mechanical steering systems are not dynamic though, you are missing the point entirely. It can't change the spacing of the teeth on the fly - steer by wire effectively does. The number of turns lock to lock on a mechanical system is almost always the same, regardless of speed. With steer by wire, you can easily implement say one turn lock to lock at low speed for easier parking, increasing to 2-3 turns at highway speeds for stability. Which is essentially exactly what the recent Lexus model with such a system does. At low speed it can turn its wheels from one extreme to the other in just 150 degrees of steering wheel rotation - no hand over hand turning etc. 150 degrees is essentially unthinkable on a mechanical rack and pinion system, as it would make the car incredibly twitchy on a highway. > https://www.motortrend.com/reviews/2023-lexus-rz450e-steer-by-wire-yoke-review/ https://www.motortrend.com/reviews/2023-lexus-rz450e-steer-b...
      - inferiorhuman 3y ago
        It can't change the spacing of the teeth on the fly. Geez, Elon really ought to start a goalpost moving company. But hey I'll play: yes, yes it can. That's precisely what BMW's active steering is, yes it's mechanical, yes it varies the ratio depending on speed, and yes it's been around for a couple decades now.
        giobox 3y ago
        BMW active steer doesn't get remotely close to 150 degrees lock to lock when maneuvering (minimum rotation reached is ~720 degrees/2 turns), or offer the infinite and instant range of adjustability you can get with a drive by wire system. But sure, it's just the same. I couldn't care less whether the system is on a Tesla or not, its just abundantly clear there are some design and packaging advantages when you lose the mechanical link in anything with a steering wheel. The vast, vast majority of rack and pinion systems ever made, both old and modern, don't adjust number of turns lock to lock at all, whereas the ability to essentially infinitely adjust it is inherent in all drive by wire steering systems.

XorNot 3y ago

It means where you put the steering wheel doesn't have to have a firewall penetration and mechanical linkage through to the engines. That's a lot of mechanical joints which need to be continuous, and need greasing, sealing and have limits on relative angles between them that you don't need - as well as they have to have enough strength to transmit the forces involved. By contrast, with steer-by-wire your system is essentially a black box you bolt on somewhere and then a more compact set of motors which can be coupled to the wheels at whatever is mechanically optimal. The main reason not to do it is because your control systems need to be perfect. Conversely, above a certain vehicle mass, it's also not realistic to think that a human would be able to control the car anyway if the power steering failed, or that control system failures would still be devastating (i.e. if the power steering starts fighting you, you're going to lose).

whelp_24 3y ago
Big rigs used to not have power steering, i think with adrenaline you'll be able to steer. I do concede that the power steering fighting you would be bad
- bravetraveler 3y ago
  I just want feedback from the road, wires don't give me that
  - kuhsaft 3y ago
    You can absolutely get feedback from steer-by-wire. Ask any racing sim enthusiast. Those racing sim wheels can provide enough feedback to rip the wheel out of your hands.
    - bravetraveler 3y ago
      That "feedback" doesn't meet my poorly framed hyperbole. I'm intimately familiar as a driver; both in sims and Real Fast Cars. At what point does it go from feedback to lies? Some computer saying "yep, this is what's happening", if you're lucky. I'll yield that has been the trend for eons. That said, I don't want more of it. What lead to my first comment is the understanding that Tesla doing something where it's... different wires. Bus vs Ethernet or whatever. It sounds even more muted/numb. I don't want a real car to feel like a sim. It's getting harder to tell the difference for the wrong reasons. It's not that the simulators are closing the gap, but that the cars are becoming simulators. Lowering standards is definitely one way to meet them. Take your "we have feedback at home" and keep it I'm half joking through most of this, by the way. The problem is there but I'm deliberately overstating it

bonestamp2 3y ago

It has rear wheel steering, so there would be a lot of linkage needed to do that mechanically. That said, GM has been doing rear wheel hydraulic steering for a couple decades and the front steering is still mechanical in those (at least historically, not sure if that has changed with their EV lineup).

Grazester 3y ago
Just about every car manufacture has done rear steer at some point I believe. Nissan had it done initially with a Hydraulic system then electric.
- bonestamp2 3y ago
  Probably. I know Dodge and Mitsubishi have done it too.

giobox 3y ago

Allows you to vary the steering ratio dynamically (how many "turns" lock to lock). Means a lot less arm twiddling during lower speed maneuvers, and can gradually increase the ratio as speed increases. Traditional mechanically linked steering racks (electric or hydraulic) don't do this and are the same number of turns lock to lock regardless of speed - they can only dynamically vary the amount of power assist, not the ratio. It's been something car manufacturers have wanted to do for a while. Another benefit in theory is packaging - you can free up more space for cabin, front trunk or motors etc when you don't have to route a physical steering column.

pandaman 3y ago
BMW had this on mechanically linked system for 20 years. It's called "Active Steering" in their marketing speak.
- deleted 3y ago
  [deleted]
- giobox 3y ago
  It's not really the same at all in practice though. With steer by wire you can get the lock to lock literally as little as you like - 150 degrees at low speed lock to lock in the Lexus system for example. In theory it could go from one extreme to the other in a single degree, its just software, although obviously no one sane would implement this. Active Steering on BMWs doesn't get remotely close to 150 degree low speed lock to lock.
  - pandaman 3y ago
    It's a system that changes the ratio of the steering wheel rotation to the wheel angle dynamically while still mechanically linking the wheels to the steering wheel. It does not have the same parameters as Lexus system but many other things differ between BMWs and Lexuses too.
    - simondotau 3y ago

guidedlight 3y ago

Steer by wire is cheaper to produce, as it allows you to reduce costs for RHD markets (e.g. Australia, New Zealand, UK, Thailand, Indonesia, Japan, etc). For example, Ford F-150 and RAM 1500 trucks from the US are exported to Australia where they need to undergo an expensive conversion process before they can be sold. This is why a base model F-150 is US$74000 in Australia.