2
$\begingroup$

For one axle with one wheel, can the following rules be met and if so, what would be the most simplistic implementation?

Rule #1. Axle rotates clockwise: Wheel rotates at a 1:1 ratio with the axle. The direction of the wheel compared to the axle does not matter.

Rule #2. Axle rotates counter clockwise: Wheel rotates, but at less than a 1:1 ratio with the axle. The direction of the wheel compared to the axle does not matter.

If this already exists as a part manufacturers produce, what is it called?

How far have I gotten with this concept? Not very. Having a ratcheting mechanism sounds like it'd be a necessity or possibly some kind of planetary gear train.. but I'm coming up empty for actual solutions.

The purpose of this would be to have a single motor drive a small toy car/robot forward/right when the motor rotates one way and forward/left when the motor rotates the other way. The motor would be attached to a bevel/mitre gearbox similar to the image below. The bottom is where the motor would go and the mechanism I'm describing should go on both the right and left sides along with the wheels. At least, this is what I'd envision so far to accomplish my goal.

PS: I'm really just doing this for the novelty of it. I'm just getting into electronics and this was a challenge for myself (which I need help with it would seem, lol).

Mitre Gearbox

$\endgroup$
  • 3
    $\begingroup$ Yes it can be done. Proof of existence : direct drive a freewheel in one direction, epicyclic and freewheel in the other. There may be simpler solutions. $\endgroup$ – Brian Drummond Dec 23 '16 at 16:25
  • $\begingroup$ @BrianDrummond Any chance you could illustrate how you'd implement that to affect a single wheel? $\endgroup$ – Mythics Winter Dec 23 '16 at 18:29
  • $\begingroup$ What is the full situation you're trying to solve? An axle merely supports wheels or gears. What is the power source and why does it need to be hard-mounted to the axle, for example? FWIW, I've seen an implementation where a drive gear on the axle sits on a worm-gear thread, so when the axle changes rotation direction, the drive gear shifts longitudinally, thus engaging a different planetary gear on the output wheel. $\endgroup$ – Carl Witthoft Dec 24 '16 at 2:54
  • $\begingroup$ Just to clarify - are you saying that axle #2 always rotates slower than axle #1 irrespective of rotation direction? Or are you saying the one turning 'anti-clockwise' always turns slower than the one turning 'clockwise'. So depending on which direction of spin, the slower axle actually switches between being #1 and #2 $\endgroup$ – m4p85r Dec 24 '16 at 10:11
  • 1
    $\begingroup$ The pull-back toy card have a intermediate gear that switches engagement from one position to another with different ratios, one for winding up the spring fast and the other for unwinding it slowly. $\endgroup$ – KalleMP Feb 2 '17 at 9:25
4
$\begingroup$

Sailboat 2-speed winches do exactly this. Winding the handle clockwise directly engages the drum via one ratchet, and when you wind it anti-clockwise a different ratchet engages an epicyclic gear. Both directions move the drum in the same direction, and both ratchets prevent the drum from moving backwards. The key feature is two ratchets in opposing directions.

Another directional mechanism is Bendix gears, which slide axially along a coarse spiral shaft until they engage or disengage the output gear. The direction of the torque controls which way they slide.

Another is a one-way bearing or sprag clutch; a roller bearing where one (usually the inner) race is not circular but a series of ramps. In one direction the rollers jam, in the other they are free to rotate. It acts like a ratchet.

KalleMP mentions that pull-back toy cars have a intermediate gear that switches engagement from one position to another with different ratios, one for winding up the spring fast and the other for unwinding it slowly.

I imagine that there are hydraulic solutions too.

$\endgroup$
  • $\begingroup$ The roller bearing you’re describing is known as a “sprag clutch” $\endgroup$ – Jonathan R Swift May 10 at 21:36
  • $\begingroup$ @JonathanRSwift - thanks, I've updated my answer $\endgroup$ – Robin Bennett May 11 at 22:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.