pic: Don't do this. It's a bad idea.

[Dillon Carey]

[cdm-description=photo]37012[/cdm-description]

[=Martin=Taylor=]

Not a suspension.

What's going on in those wheels? Looks like a lot of linkages.

[Cuog]

Looks like a psuedo suspension. The wheels look to be able to tilt up/down which would help a little in covering uneven terrain. One problem is that the pivot for the suspension is in a different plane than the U-Joint so there would be a tendency to try and stretch the U Joint unless it has something like a slip-yoke.

[Marc S.]

Looks like a possible crab module, with 2 wheels spread apart for stability, a differential in the center for better turning and U-joints for smooth suspension. Maybe next years surface will be very bumpy.:rolleyes:

[MrForbes]

Looks like the robot version of an automotive Independent Rear Suspension (IRS).

That's a really neat project to do when you're bored! nice

[SenorZ]

Maybe next years surface will be very bumpy.:rolleyes:

I think a rough terrain game is inevitable... and would be very cool. There seems to be a lot of teams that perfect their preferred drive train in the off season and spend the time during build season focusing on game play. Making a bumpy playing field could help, er, level the playing field for newer teams... like mine!

[Chris is me]

Okay, I'm going to try and describe this. It's a swerve module with a differential connecting both wheels, and flex couplings to allow for some sort of suspension.

I can't possibly imagine its use in FRC.

[Andrew Schreiber]

Okay, I'm going to try and describe this. It's a swerve module with a differential connecting both wheels, and flex couplings to allow for some sort of suspension.

I can't possibly imagine its use in FRC.

Coaxial swerve modules with a suspension and differential aren't normal. But on Winnovation they are.

Winnovation: Not even once.

[Michael Blake]

I can't figure out why you have four Bevel gears (forming a box, differential?) connected to the left wheel... couldn't you achieve the same by extending the shaft from the right wheel directly to drive the left wheel?

THANKS!

[lemiant]

I can't figure out why you have four Bevel gears (forming a box) connected to the left wheel... couldn't you achieve the same by extending the shaft from the right wheel directly to drive the left wheel?

THANKS!

Actually the box results in the two turning in opposite directions.

[MrForbes]

The differential is used in the drive axle of cars, read about it

http://en.wikipedia.org/wiki/Differential_%28mechanical_device%29

[Michael Blake]

Actually the box results in the two turning in opposite directions.

RIGHT, but you wouldn't want them to turn oppositely, correct?

This has me scratching-my-head... ;-)

[EricH]

Actually, Michael, lemiant didn't have a chance to read squirrel's link yet. I would suggest reading that link, then figuring out the drive system.

Short version: If both can go the same way at the same speed, both go the same way at the same speed. But if one of them can't keep that speed up, then it doesn't have to due to the way the differential is set up.

[Tristan Lall]

Wouldn't this work better with constant velocity joints (rather than universal joints)?

And are you using the universal joint as two of the members in a four-bar linkage that holds up the wheel? If so, isn't it just going to deflect to the maximum? (Or am I missing a spring somewhere?)

This would be a fun stock design to keep around...just to tempt people when FIRST decides to give us some real obstacles.

[Cuog]

http://www.youtube.com/watch?v=vBm-SzO3ggE&feature=related

Here's an animation of how a differential operates for those confused.

[MrForbes]

Here's a much better explanation.....but then, I do like old stuff

http://www.youtube.com/watch?v=F40ZBDAG8-o

[Michael Blake]

Short version: If both can go the same way at the same speed, both go the same way at the same speed. But if one of them can't keep that speed up, then it doesn't have to due to the way the differential is set up.

So, where's the "slippage" provided in this setup?

THANKS!

[Hawiian Cadder]

Why not choose pneumatic tires over the suspension? I don think you would get much "play" before the bevel gear bottoms out.

[Cuog]

So, where's the "slippage" provided in this setup?

THANKS!

There is no "slip"* in a differential. The nature of how the gears mesh is what allows the shafts to turn at differing rates. The differential itself has no control over the situation, its just along for the ride.

*(unless we start talking limited slip differentials and lockers etc)

[EricH]

So, where's the "slippage" provided in this setup?

THANKS!In the differential gearing. Two of the 4 gears in the inner box are connected to the wheels; the other two are idlers. The relative speed of the wheels doesn't really matter to the idlers; they'll move as fast as they need to.

Hint: Think of this setup as 2 gearboxes. The inner box is the 4 in the middle of the "axle"; the outer is the bevel at the top and the large gear it meshes with.

[Michael Blake]

Here's a much better explanation.....but then, I do like old stuff

http://www.youtube.com/watch?v=F40ZBDAG8-o

NOW, _that_ was helpful... ;-) THANKS, Jim!!

[Michael Blake]

In the differential gearing. Two of the 4 gears in the inner box are connected to the wheels; the other two are idlers. The relative speed of the wheels doesn't really matter to the idlers; they'll move as fast as they need to.

Hint: Think of this setup as 2 gearboxes. The inner box is the 4 in the middle of the "axle"; the outer is the bevel at the top and the large gear it meshes with.

Also, helpful... THANKS, Eric!

[lemiant]

Actually, Michael, lemiant didn't have a chance to read squirrel's link yet. I would suggest reading that link, then figuring out the drive system.

Short version: If both can go the same way at the same speed, both go the same way at the same speed. But if one of them can't keep that speed up, then it doesn't have to due to the way the differential is set up.

I hadn't. I thought the big bevel was attached to the shaft not the box. After reading that article I understand, and am amazed!!!! :ahh:

[AdamHeard]

Wouldn't this work better with constant velocity joints (rather than universal joints)?

And are you using the universal joint as two of the members in a four-bar linkage that holds up the wheel? If so, isn't it just going to deflect to the maximum? (Or am I missing a spring somewhere?)

This would be a fun stock design to keep around...just to tempt people when FIRST decides to give us some real obstacles.

I Agree with your complaints about suspension geometry.

Also, The suspension on this seems to indicate a purpose of driving over varied terrain. With the completely open differential on there, the wheel with less resistance (often in the air, not making any contact) will get all of the rotation, leaving a torque on the static wheel equivalent to just the friction in the differential.

[Hawiian Cadder]

I Agree with your complaints about suspension geometry.

Also, The suspension on this seems to indicate a purpose of driving over varied terrain. With the completely open differential on there, the wheel with less resistance (often in the air, not making any contact) will get all of the rotation, leaving a torque on the static wheel equivalent to just the friction in the differential.


true, maybe you could use a limited slip differential to prevent that.

[PAR_WIG1350]

I Agree with your complaints about suspension geometry.

Also, The suspension on this seems to indicate a purpose of driving over varied terrain. With the completely open differential on there, the wheel with less resistance (often in the air, not making any contact) will get all of the rotation, leaving a torque on the static wheel equivalent to just the friction in the differential.

The suspension Appears to actually a three bar linkage with the link from the wheel bearing retainer to the differential frame being a spring loaded variable length link (possibly a gas shock). The u-joint is simply the joint between two links. It would benefit from more support, but the geometry should still work.

Also, by linking the axles with a slip clutch between the output gears of the differential the static wheel issue could be resolved. Like this (http://www.chiefdelphi.com/media/photos/30718). basically it's a primitive version of the limited slip differential.

[MrForbes]

That method of using the axle shaft as a suspension locating member was used on some IRS cars for years, including the Corvette starting in 1963

[Cuog]

That method of using the axle shaft as a suspension locating member was used on some IRS cars for years, including the Corvette starting in 1963

Also known as a "Swing axle"

First on this list: http://www.autozine.org/technical_school/suspension/tech_suspension2.htm

Also used on VW Beetles(busses, and most other models including porsche) 38-68

[MrForbes]

There are different ways of doing it, the Corvette used Ujoints at both ends of the axle shaft, so it isn't really a swing axle like the early VW. The axle and control arm make a parallel arm setup, so the camber doesn't change dramatically like on the early bug

[Dillon Carey]

This was just a fun project, we probably will never make anything like this.

Also I thought about making it into a limited slip diff. but I ran out of steam before getting that far.

As far as the suspension is concerned, I put it in there just so if the robot got tipped a little by another bot, it could still get some power to the floor. And I have never done anything with any sort of suspension, so I'm sure it is probably a terrible setup.

Last, the entire reasoning behind a differential module was to be able to have lots of traction, while still being able to turn the module.

[Borisdamole]

There are different ways of doing it, the Corvette used Ujoints at both ends of the axle shaft, so it isn't really a swing axle like the early VW. The axle and control arm make a parallel arm setup, so the camber doesn't change dramatically like on the early bug

but Corvette is using that strange leaf spring setup....

And this drive train could improve traction by using a sealed diff, and using silicone diff fluid to prevent the module from "diffing out"

A limited slip diff is normally all mechanical, and uses helical gears to prevent "diffing out" (but there are others that operate on clutches or springs)

a traditional limited slip setup would be VERY costly for this size (the gears would be expensive), but silicone would be a great option....

Many small differentials are easily available from any rc car shop or ebay

Cool idea!

[Aren Siekmeier]

Odd how this comes out the day before I return from a week long vacation when I had enough time to think this up in my head. This is exactly what I was envisioning, mechanically anyways: a swerve module that can be pivoted effortlessly due to the differential box.

Several people have explained it already, but I'll take a stab too. You turn the coax shaft as usual and it turns the differential box turning both wheels, like a normal differential drive (this also allows for some interesting turning cases without most of the wheel scrub). Turning the module drives the wheels in opposite directions while the differential box remains stationary. He added the fourth bevel in there just cuz (for strength?), it seems to me, as most differentials operate with only three. Now try flipping one wheel's input to the box (by putting the two perpendicular bevels on the same shaft or any of a number of other things), and now it can translate freely, but must be powered to rotate.... An interesting, though usually useless, prospect.

The universal joint suspension was definitely not something that entered my head. Why you would ever need that, no one knows. Then again, why would you ever need any of this? It's just awesome, that's all.

[Borisdamole]

He added the fourth bevel in there just cuz (for strength?), it seems to me, as most differentials operate with only three.

Mechanically 3 will work, but it creates alot of load on the center gear.

Acutually many diffs use 4 center gears(total of 6 gears)
like this (http://www.bbssystem.com/buggy/diff3.jpg)

[JesseK]

iirc, this is eerily similar to the front landing gear for planes.

[MrForbes]

Acutually many diffs use 4 center gears(total of 6 gears)


Most of the automotive differentials I've seen use two "spider" gears, for a total of 4 gears. The only common exception is the heavy duty Ford 9" rear from the 1970s-80s. But I haven't worked on many late models either!

[Chris is me]

iirc, this is eerily similar to the front landing gear for planes.

The suspension is definitely similar, but I thought the landing gear for planes were unpowered casters? I'm no expert by any means, though.

[Ian Curtis]

The suspension is definitely similar, but I thought the landing gear for planes were unpowered casters? I'm no expert by any means, though.

No, the nose gear is actuated for taxiing. The rudder is very ineffective at low speeds. Think about it, would flapping the rudder around give you a whole lot of moment when you are sitting on the ramp? Some very old planes have a tail skid in place of a nose wheel, and occasionally this isn't actuated (but it makes ground handling a royal pain).

[Garret]

I may be wrong, but I don't think that this will even offer the right type of suspension. From the picture it looks like there is only one universal joint on each side, meaning that the wheel can only rotate up and down, not just move up straight up and down as in a more traditional suspension. I would think that there would need to be at least 2 universal joints on each side in order to allow it to move up and down. However I do like the idea a lot.

[Tristan Lall]

No, the nose gear is actuated for taxiing. The rudder is very ineffective at low speeds. Think about it, would flapping the rudder around give you a whole lot of moment when you are sitting on the ramp? Some very old planes have a tail skid in place of a nose wheel, and occasionally this isn't actuated (but it makes ground handling a royal pain).On most aircraft using tricycle gear, the nose wheel is unpowered, unbraked and mechanically or hydraulically steered.

There are numerous exceptions, however. Some early Boeing 727s had nose gear brakes, but they were omitted on later aircraft (and often removed on early ones) because the added braking capacity was of little use compared to the weight penalty (something like a hundred pounds). There was an aftermarket kit being evaluated by Air Canada on one of their Boeing 767s which added an electric motor to the nosewheel for taxiing. While saving wear and tear on the main engines was a good idea (I believe it could run on the APU's generator), again, it weighed too much, and there was concern it could lead to higher maintenance costs for the nose gear assembly. On a few small aircraft (Diamond's DA20, for example), the nose wheel is freely castering. Steering is accomplished with the toe brakes controlling the main wheels (differential braking), and the rudder pedals at higher speeds.

Incidentally, the suspension on the nosewheel of most aircraft is not located beside the wheel like that—it's usually in the strut. (Gas-over-oil is common.)

[PAR_WIG1350]

On most aircraft using tricycle gear, the nose wheel is unpowered, unbraked and mechanically or hydraulically steered.

There are numerous exceptions, however. Some early Boeing 727s had nose gear brakes, but they were omitted on later aircraft (and often removed on early ones) because the added braking capacity was of little use compared to the weight penalty (something like a hundred pounds). There was an aftermarket kit being evaluated by Air Canada on one of their Boeing 767s which added an electric motor to the nosewheel for taxiing. While saving wear and tear on the main engines was a good idea (I believe it could run on the APU's generator), again, it weighed too much, and there was concern it could lead to higher maintenance costs for the nose gear assembly. On a few small aircraft (Diamond's DA20, for example), the nose wheel is freely castering. Steering is accomplished with the toe brakes controlling the main wheels (differential braking), and the rudder pedals at higher speeds.

Incidentally, the suspension on the nosewheel of most aircraft is not located beside the wheel like that—it's usually in the strut. (Gas-over-oil is common.)

Another exception would be the Boeing B-52 Stratofortress Which has a quadracycle undercarriage and 4-'module' crab steering to facilitate landing the behemoth of an aircraft in high crosswinds conditions. Most aircraft have to approach flying sideways and straighten out after they land to roll down the runway instead of off it, the B-52 simply rolls sideways :p .

[Tristan Lall]

Another exception would be the Boeing B-52 Stratofortress Which has a quadracycle undercarriage and 4-'module' crab steering to facilitate landing the behemoth of an aircraft in high crosswinds conditions. Most aircraft have to approach flying sideways and straighten out after they land to roll down the runway instead of off it, the B-52 simply rolls sideways :p .To be fair, the B-52 only has ±20° of strafing ability.

Actually, the reason for those steerable gear is the use of ridiculously-small control surfaces on the B-52. The engineers designing it in the late 1940s were not confident in the reliability of early hydraulic flight controls, and therefore adopted all sorts of unusual compromises. Instead of using a large hydraulic rudder to control the plane in a crosswind, they just added steerable gear, and stuck with a very narrow (though still about 20 ft tall) spring-tab-assisted rudder.

It seems to have worked, because the early-1960s-built B-52Hs are likely to be in service for at least 30 more years....