Torque 'Spring Load Differential'

[SNIPE]

Hi,

Today and over the past few days I've been working on a way to have wheels driven for a 4x4 but to have as maximum torque, then I came up with the idea to use a worm gear drive but to add springs to it so if it gets stuck the springs get compressed by the worm gear and that then gives more torque to the spur gear, I also added a center differential to swap the torque between front and rear wheels, the result is quite good especially driven that there is not much weight on the car yet and slick-ish tires with no suspension or steering.

Here is a video of it working

Edited June 8, 2014 by SNIPE

[Zerobricks]

So what you basically did was to add slack to the driveline? Sorry I dont see any benefits from the springs?

[SNIPE]

I'm unsure I follow

The springs definetley help as when you grab the axle to try and stop it you can feel the spring(s) providing more torque so its hard to stop it completely.

The worm gear acts as a gear strip as well as a worm gear when the car gets stuck, the axle through the spring and worm gear doesn't slide, it only rotates.

Edited June 8, 2014 by SNIPE

[Zerobricks]

Springs dont magically generate torque....You get the same torque without springs....

EDIT to clarify where does the force come to compress the spring? Worm gear!

Edited June 7, 2014 by Zblj

[DrJB]

Well, what the OP did not mention, it could be that the springs are pre-loaded, and in such case, there is no slack. Thus, I am with the OP and such construction may have merit. The springs simply 'store' some motion if the wheels get somehow stuck. They then restore it when enough torque has built-up. Rather clever, and warrants further 'play'.

Edited June 9, 2014 by DrJB

[Kelkschiz]

I am not a mechanical engineer but i have to agree with Zblj. The process SNIPE describes should not be able to generate torque. It feels a little like a perpetuum mobile; it appeals to logic but just misses the mark. You could easily test it: Just measure the torque with and without the spring.

[SNIPE]

The springs are pre-loaded yes by a little bit, maybe I'm confusing torque with traction (i'm terrible at this) but heh, it works, I can see the wheels moving slightly to try and get grip like with a differential on an off-roader however this is acting like a locked diff but I guess you could make it switch between locked and unlocked by putting an 8 tooth clutch gear in instead of a 24T then adding a clutch.

Also: Perpetual motion doesnt exist

Edited June 9, 2014 by SNIPE

[touthomme]

Cool idea! You may want to set up some better lighting for future videos. :)

J

[Nazgarot]

The springs do not add torque. They store it.

When the wheels get stuck the spring is compressed (motor stores force in the spring), and both the force of the motor and the added force from the spring is supplied to the wheels.This gives the wheels gradually more torque when they become stuck til the point where the spring is fully compressed. At that time the force (torque) applied to the wheels is the maximum force of the spring + the motors torque.

This is actually a good way to momentary increase force to free stuck wheels. On the other hand I've never had problems with the power applied to the wheels being to low... More like the gears not being able to handle the torque when the wheels get stuck.

-ED-

[locoworks]

the springs add nothing to power or overall torque. they actually reduce power to the wheels as they compress. the motor can only generate so much power and if it is comporessing a spring it isnt turning the wheel. once the spring is compressed the wheels are getting as much torque as the motor could provide without them. what the spring will do ( though maybe of no great use ) is to give a sudden increase in the speed of wheel rotation for 1/4 - 1/3 rd of a rotation of the wheels whilst not under load. they may act as a bit of a cush in the drive train though which may just save a gear???

[emilstorm]

I think I get what you are trying to do with the spring, but I don't see it doing it. I don't think a spring that little is going to do much difference anyway, interesting concept though.

[andythenorth]

Compressing the spring is parasitic - it requires force from the input axle.

For a single axle, with a direct motor drive, the diversion of force into compressing the spring would reduce the force transmitted to the spur gear.

For a set-up with a differential, I am not good enough at physics to figure out the overall split of torque between the two axles

Edited June 8, 2014 by andythenorth

[SNIPE]

Hi

I have made it so the wheels can be locked to the worm gear drive or so it can free wheel (this is useful if the car is starting to tip over, simply unlock the necessary axle, I also added a second spring so it works in reverse gear too.

Upon testing it seems that when the load is too high it is automatically switching the axle to 'unlocked' but I can disable it from doing that by adding the old axle connector with ridges to use with the clutch, I think ill use some stronger springs soon too.

Edited June 8, 2014 by SNIPE

[andythenorth]

What kind of terrain are you using this on? What you've built is a torque-limiter, not a torque-multiplier

In lower-friction situations, applying the full torque to a wheel can cause it to break away and spin. In this case a lower torque will maintain traction. It's the same theory as driving a car in higher gears on snow.

[SNIPE]

Not sure yet i've tested it on ramps and it can get up quite steep ramps fine, and can get on ledges or drops that are around 2.5 inches tall

I need to improve the torque now as replacing the 24tooth gear has gave it less but I should just be able to do that on the cabin side of the drive shaft or maybe by using shorter but stuffer springs.

Lets say its trying to get up a ledge, the wheels are stopped but move slightly, sometimes it swaps between front and back wheels and it usually works fine and enables it to find grip to get up the ledge it does need some improving however.

Fitting the steering arms and steering gear/rack is gonna be tough.

Edited June 8, 2014 by SNIPE

[emilstorm]

These springs will have to be absolutely enormous for it to have any kind of effect, especially with load on the axle. Having a spring on each side of the worm gear will neutralizy any effect you might get out of this discharge. It is a little unclear in the video, but if you put the chassis belly up and block a wheel to store energy in the spring, does it have any noticable effect on the wheel when you discharge the spring?

As i said in my earlier post, i think it is an interesting concept to store propulsion energy this way for when you need a little extra. And it is quite brilliant that it would automatically start charging when such a situation arises, but i don't quite believe it will ever have any practical and measurable effect. I think the sudden increase in speed you see in your video would more or less come without the spring when the worm gear reaches the end of its "free run".

Any way i don't really see any practical value since a regular differential wiil do the same. If you however make the "free run" long enough for the wormgear to slip entirely off the gear, and be pushed back by the spring when the other set of wheel gets the vehicle past the obstacle, it would be an interesting new take on a differential. It would probably not be very reliable though.

But it is definedly an interesting technique

[SNIPE]

When the spring is discharged it has an effect on the wheels yes they spring forwards with force. (because the spring pushes the worm gear forwards like a gear rack back to its original position) but depending on the surface it can move a little bit not fully compressed and decompressed. I don't think the spring has to be huge - you can give it more travel by making it stiffer but shorter instead of longer but weaker strengh.

If I take the spring out, it will move too quickly and will apply the same torque all of the time and wont be as good for crawling , the trick is to move at low speed over the surface so the car doesn't tip up but go fast over say wet mud where it would get stuck (not that i'm putting it in mud)

Edited June 8, 2014 by SNIPE

[emilstorm]

If I take the spring out, it will move too quickly and will apply the same torque all of the time and wont be as good for crawling , the trick is to move at low speed over the surface so the car doesn't tip up but go fast over say wet mud where it would get stuck (not that i'm putting it in mud)

Ok, then it's maybe just me being dense, but isn't that pretty much just a length differential?

[SNIPE]

I've took the reverse spring out because it doesn't really help much and uses up space for the forward spring also the spring cannot be pushed up against a pinhole because the chamfering causes the spring to get stuck and not rotate with the axle, I don't want the spring being wound onto the worm gear! so I just added a half bush between the hole and the spring.

When I added the clutch gear it can disconnect the wheels from the motor but it also adds some slack since the teeth between the gear clutch and e clutch are far enough apart.but it isn't too bad.

I'm not sure what a length differential is but it is like a differential yes.

Edited June 8, 2014 by SNIPE

[emilstorm]

I'm not sure what a length differential is but it is like a differential yes.

Sorry, I don't even know if it's called that. I mean the diff between the front and back wheels of AWD's.

I think yours works sort of like a reversed differential, it seems to stall the set of wheels that looses traction instead of making it spin faster. This concept gets more interesting the more I look at it, I wll stay tuned

[SNIPE]

Nah there is already a regular diff in the center.