Friday, January 6, 2012

Self-steering car chassis, Mark II

Opener

Some may remember a very simple self-steering chassis I've tested last February. It was about time to advance it, so here's a new self-steering chassis concept, Mark II.

Let's just quickly remind ourselves what the self-steering chassis is about, and when would one prefer it over typical designs. Namely, if a planned vehicle is limited to using only two motors altogether (due to weight, power requirements, size, simplicity or any other reason), a conventional approach would use one to provide drive, and the other to steer. However, for some particular models it might be troublesome to use only half the available power for providing drive.

Otherside An alternative is to have both motors provide drive, one for each wheel. In such configuration, steering is done by having the two motors (and of course, their respective wheels) turn at different speeds, thus producing sufficient tangential force for the chassis to turn. This type of drive, often known as a differential drive, is used by tanks, for example. However, if the chassis is wheeled, it will turn too ― at least if the front wheels have sufficient caster to readily follow it, what was the point of the aforementioned Mark I chassis. But it still suffers from poor reliability unless perfectly balanced and having minimal friction, both of which are sometimes unavoidable. Therefore, an obvious direction for improvement is to introduce a steering control that follows the drive wheels' behaviour.

Mark II concept attempts to solve this problem mechanically. To explain its functioning, let's split it down to a few main components.

Scheme Each of the rear wheels' axles (A) is linked to a differential several studs ahead (B). As you have perhaps noticed, there are three gears (C) on one, and four at the other side, resulting in one of the axles spinning in reverse. The differential thus works opposite from its typical application on the half-axle: it actually turns only when the rear wheels aren't turning at the same speeds (i.e. they tend to steer), and its rotation speed is proportional to the difference between the rear wheels' speeds. But as long as the rear wheels turn simultaneously, it remains stationary.

In other words, its turning speed is proportional to the amount of steering that needs to be done by the front wheels ― of course, also obeying the direction. But since it's the speed and not the absolute displacement we're interested in, this differential cannot be directly linked to the steering pinion. Instead, we need a simple sort of a mechanical tachometer, and that is approximately what the front differential (D) does. It has got a very light brake (E) at its main axis, and its second axle leads to a usual steering rack&pinion mechanism (F).

The point is that the brake and the rack&pinion work in balance: the more torque and speed arrive from the rear differential, the more will they be met by the increasing resistance of the brake, thus directing more towards the steering. The steering, of course, imparts its own resistance depending on how sharp turn it's attempting to make, and yet more if it's equipped with a recentering system (G). Exact steering would need a very precise balance between these variables, but in practice it needs no more than a nudge in the correct direction, and then the friction to the ground keeps it in correct geometry. In other words ― it works.

Scheme-EditedWhen there is no need to steer anymore (the rear wheels begin turning at the same speed), the rear differential will stop turning, and it will be easier for the front wheels to recenter themselves thanks to a bit of caster. Unless the weight on the front axle is huge and the tyres grippy, this force will be very light ― and that is the main reason why the pinion couldn't be linked to the rear differential through a standard clutch gear: its resistance would almost always be too high, and prevent the front wheels from recentering. Very heavy models may still get away with it, though ― but they rarely have limits on the number of motors anyway. The better but more complex solution is to introduce a recentering mechanism and adjust its force carefully according to the rest of the system, in which case the caster is not necessary.

There are still some particular situations in which Mark II works poorly, such as turning in place (with rear wheels turning in opposite directions), turning slowly in sharp curves, and driving backwards if the steering is centered only by caster (without recentering mechanisms). However, in typical circumstances it works all right.

15 comments:

  1. Great concept. Is it somehow possible to combine this idea with an independent suspension for each wheel?

    ReplyDelete
    Replies
    1. Sure, this concept is completely independent from the type of suspension that may be used. Live-axle, independent wishbones, trailing axles... anything would work.

      Delete
  2. Cotton directing wheel covers are much sought after in light of the fact that they arrive in an extensive variety of hues, outlines and examples. You can purchase a few spreads for your vehicle and change them as and when required. My Wheel Covers

    ReplyDelete
  3. This article explains what GAP insurance is, and relevant factors to consider in determining whether or not you should purchase GAP Insurance. Many consumers don't understand GAP insurance, and pass it up when it would be a wise investment to purchase it. Likewise, there are circumstances under which GAP insurance would be a complete waste of money. Learn what to look for when determining whether to purchase GAP insurance.www.protectourcar.com

    ReplyDelete
  4. Always remember that you are the customer, and you shouldn't let the car sellers pressure you into buying the used car right away. You should always ask them for some time to think about it.
    automatic car starter

    ReplyDelete
  5. Remember that it is your opportunity to test the car, so set aside your opportunity to judge whether it is a solid match and it is in a decent condition or not. Acura Lug Nut Torque

    ReplyDelete
  6. The site was so nice, I found out about a lot of great things. I like the way you make your blog posts. Keep up the good work and may you gain success in the long run.Cupertino security service

    ReplyDelete
  7. The new pull / push nature of the market powered by the Internet requires automotive advertising agencies to focus on people vs.https://www.uberafricaforum.com/uber-phoenix-office/

    ReplyDelete
  8. What happened to Corner? This blog on car insurance is not as good as his previous blogs. Corner

    ReplyDelete
  9. Try not to enable yourself to fall into this classification, as it isn't baffling for the two gatherings yet it will definitely cost you more cash then what you expected to spend. https://www.adlist24.com

    ReplyDelete
  10. It's constantly amusing to investigate new places, yet a luxury vehicle makes it significantly all the more energizing for you. rent a ferrari in italy

    ReplyDelete
  11. Including a honest to goodness Wheelskins cover should take around 60 minutes. You needn't bother with exceptional instruments or abilities to finish the establishment. Your fit ought to be immaculate, giving you a decent tight cover. You can outline your cover from a decision of 15 hues.Best leather steering wheel covers

    ReplyDelete
  12. Reinsurance offers any automobile dealership the chance to develop to the following level by offering cases to clients with the expanded power over the reinsurance company.reinsurance companies

    ReplyDelete
  13. Be that as it may, since they work for commission, they are under more strain to snatch an arrangement as quickly as time permits.
    click over here

    ReplyDelete
  14. Brilliant post. I was looking like this. Genuinely it is to an unprecedented degree obliging and educational post. Thankful for sharing. Sacramento Background Check

    ReplyDelete