Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

As some of you noticed, I've been asking a few questions here and there. And a few of you have asked what's up. Well, I've been doing some brainstorming regarding an all-direction drive system (I think you all have a special term for it; but for the life of me it escapes me).

It seems that the simplest and easiest way is to employ the use of omniwheels setup in a perpendicular fashion. But I'm not keen on the idea of splitting up the motor power of the robot between the two directions. Nor the seemingly lack of traction when compared to some other robots (as you really only have two wheels that will be opposing the force; the other two will just roll with it)

So this is what I came up with for my ideal drive system:

1) All the wheels can steer 360 degrees
2) All the wheels can individually go forwards or backwards while having a single motor set, gearbox, and transmission power ALL the wheels.
3) At least a two speed transmission (though to be honest, I'd really like to have an ULTRA-low gear as well)




1) All the wheels can steer 360 degrees

After thinking about this one, I figured there's no point to having the wheels steer individually; that is, to be able to have them facing different directions. While the thought of having them all opposing each other in order to combat being pushed, I figured it might be better to instead have them turn in the direction of the force and use the motors to push back.

So I came to the conclusion to develop a steering system in which turns ALL of the wheels simultaneously. I concocted one system (that has two variations) that seems to do the trick. I'll probably post another animation of it when I get the chance to model it (probably tomorrow evening), so I'll come back to this later.



2) All the wheels can individually go forwards or backwards while having a single motor set, gearbox, and transmission power ALL the wheels.

This is one of the bigger problems I've been facing. When I was putting such a drive system through the ropes (in my head) it dawned on me that as the wheels turn, in order for the robot to spin, the wheels that turn backwards/forwards change. That is, say the wheels are all pointing forward and you want to turn right, well, simply you spin the left wheels forward, and the right wheels backwards. Voila. So I originally thought to have two drive systems; one for the left wheels, one for the right wheels. BUT, say the wheels are all facing left: now you want the forward wheels to spin backwards, and the rear wheels to spin forwards in order to turn the robot.

So now I'm faced with two choices: a) Build a motor-mount, gear box, and transmission for EACH of the four wheels
or
b) Use a single motor-mount, gear box, and transmission that would power ALL the wheels simultaneously AND develop some sort of method to reverse that power for individual wheels.

And personally, while a) MIGHT be the more feasible choice... to my knowledge, option b) hasn't been explored much. And it might turn out to be a good choice too; this would save grief having to build four gear boxes, four motor mounts, and four transmissions. Plus I like a challenge; I want to see it done :P



3) At least a two speed transmission (though to be honest, I'd really like to have an ULTRA-low gear as well)
I hope this is pretty self explanatory. Ultimately, in a perfect world, I would like to have a high speed, low-speed/high torque, and an ultra-low-speed/ultra-high-torque gears. I want this drive train to get down and dirty; and if need be, it will drive slow... but it will certainly move whatever is infront of it.




Now, with regards to 1), I do have a question concerning the idea in my head. I can't elaborate on the idea now, but I will tomorrow evening when I get the time to. But just a quick question: I see chains used all the time; but always in a vertical fashion. Is it feasible to have the chains run horizontally? Or will it be very prone to slipping off the sprockets? If so, what can one do to counteract that from happening?



In regards to 2), you can read up on my "reverse gear" thread here: http://www.chiefdelphi.com/forums/sh...ad.php?t=28174



And finally, in regards to 3), I saw the team 222 3 shifter design that has balls pop out of the shaft to engage the proper gear. (http://www.chiefdelphi.com/forums/sh...threadid=26630) That seems like a grand idea; I really like it. But I also read some cautions regarding the design. You think the design is quite alright to use so long as you take the proper precautions (i.e. material selection/lubrication)? Any other three shifters? Maybe I can use that 4 speed automatic shifter ;) Though to be honest; I prefer to have the shifting in the power of the driver, so if I did implement that, I'd program in an override switch. You think it'd be simplist just to use a single small pneumatic to engage a 2nd gear instead? Beauty part of this is I want to have only ONE transmission in the robot; no need to build two transmissions and mount double the parts.



So yeah; I'm a newcomer to mechanical engineering, so I'm looking for your input; and so far it's been great! And I have one problem that seems to be just out of my reach right now. And that is transferring the power of the motors (from a fixed shaft... or gear... or chain, or what-have-you) to a 360-degree spinning wheel. I'm sure it's been done before, but I haven't seen any threads (though admitadly, I didn't look through ALL of them... but a half decent number none-the-less) regarding that issue.

So thanks again on any input and advice you can toss my way! You've been a great help so far!

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Congratulations, you've just reinvented Swerve Drive. I suspect you have already seen some robots like what you describe in action, and just didn't know it. Actually, its amazing the depth to which you have conceptually predicted designs wrought from tough trial and error. Now that you know its out there, I bet you'll have better lucking finding pictures of such systems on CD and the net. In particular i remember seeing a system using two gearboxes routed out to the four corners with horizontal chain, which sounds close to the design you were moving towards. To my knowlege no one has been using gears to switch directions, though. yet.

To get you started, these videos of 118 in action are what first got me excited about swerve drive:
http://chiefdelphi.com/forums/showth...ight=118+video

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

I have been considering ways to make a drive train like you are describing (and i have thought of the one you suggested) and i came to the conclusion that that method is to complex mechanically. As you can see from the reversing gear box that you put in the post you linked from, the reversing system is quite complex. Basically, i dont think its practical. As jim said, what you described is basically a swerve or crab drive is much more do-able (and has been done).

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

My suggestion to you guys would be, look in the White papers, and also considering contacting teams like 111 Wildstang or 79 Captain Krunch. There are others ( such as 118 the robonauts ) but I know both of those teams produce beautiful versions of what you described, in 2 slightly contrasting methods. They also both produce detailed Inventor drawings of their drives. 79 used the " crab/swerve " drive this year, and wildstand only used it in their front 2 modules. But I'm sure that both of these teams would be willing to answer any questions you may have, or direct you to drawings of what made in the past and problems they have run into.

Tho this drive is a bit more complex than others, if built correctly, with others mistakes in mind, it can be quite a beautiful piece of machinery. It is deffinitely not beyond us FIRSTers, because so many teams have produced these style drives before.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Ok, I willtry my best.
For the horizontal useage of chains, yes. It is done. Here is a rather complicated pic.here

There is another way. it looks like this M module in the corners drive sprocket in the "v" of the m.
The single chain slant inward for tension to the only driven sprocket. when it turns all four of the modules turn.

What is a module you ask...
Tytus knows best. Here is a pic of the many posted here on CD. Much help and other pics can be found in the beginning section of the 2003 robot showcase picture galleries. http://www.chiefdelphi.com/forums/pi...&quiet=Verbose It is driven throught a powered shaft coming werticly throught the center of the module. It takes a 90 degree turn with two gears ans dives a sprocket which chain drives the sprocket on the wheel. The round disk at the top is where the "bevel gear" is. It is run by the horizontal chain. It is a bevel gear I assume because It has the hole in the middle for the wheel drive shaft to go through. It rotates the whole module. There are not teeth shown in the linked pic.

Ok. now the matter of powering the shaft that goes into the modules. Take from the gearbox, the output shaft. Gear it 1:1 four times, so you knwo have 4 different output shafts. Make a reverse gear like your previous threads inclde for each of these shafts. then, make a braking system for these shafts. Like disk brakes on a car. Now, each of the shafts can run at different speeds in forward and reverse. Then you have to get these shafts to each respective module.

This system in my mind is very overweight due to the 4x braking system and 4x reverse gears. Just an idea. Although it may be crazy. It is a challenge.
It would give you what you ask at the price of weight. Also keep in mind that all four wheels will be running off of one motor, or however many you have in your gearbox, which each have a 40 amp limit.

Wew. Done. Sorry if I am unclear it is late. Ask me about the foggy parts. I hope Tyus will make an apperance in this thread too. He knows whats up and down in the swerve world.

PS
lego systems are also shown in the beginning of the 2003 picture gallery, robot showcase. They also give a good swerve module description.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Maybe I'm just missing something but if you have a drive system like in this pic, why would you need reversing gears? What is wrong with reversing the motors? I'm confused.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Best I can figure, it allows you to rotate in place.

We had a swerve drive last year (2003), and we've brainstormed for days on end about the possibilities, so I'd like to think my brother and I could answer some of the questions you might ask.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

That pic just shows the useage of a horizontal chain to turn the modules.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Here is a design we have been working on for 2005. Features: 4 wheel drive, 6 drive motors in one gear box, 2 speed trans, very low CG, 4 wheel steering crab and conv., weight as shown 90 LBS!!

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

1 more view

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Disgusting.



In a good way.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

If the wheels can all turn 360 degrees, then you only need them to turn in one direction. Just point them 180 degrees from 'front' and you've got reverse.

95 acutally produced a drive system something like what I think you mean for the 2003 season. All the wheels were inpendently steered and powered. Drills and Chips for drive, Globes and window motors for steering. The drive motors gearing was through worm gears. I've included a link to some pictures on 95's website. Anything in the picture gallery that is from 2003 may be of some use.

-Andy A.

95's photo page

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

I hope that the drive train is not detailed in your drawing. There is a need for slip clutches in the differentials to allow turning. Without them the drive motors go into stall during turns. Just two drills or two Chalupas driving the wheels means 200+ amps during turns. Add the two FP, two Chalups and two drills and you have exceeded the current capabilities of the battery and possibly tripped the 120 amp breaker. There was a GM team who had a similar design without the clutches and they repeatedly set the drill motors on fire during turns using one drill for front and one drill for back. This is one application where current sensing is an eye opener. Sorry.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Thanks for the plethora of responses!

First off Henry; that was exactly what I was thinking for rotating the wheels... in fact exactly; that was the two options I had in mind; the X and the M shape for the chains. Good thing aboot the M is that it uses less chain (right?), but if the chain falls off, then we won't be able to steer. With the X, more chain, but if one falls off, we still have three steering wheels right? Though... I suppose that won't really help. I think I like the M better.

I was thinking aboot it again last night, and I figured that all the wheels wouldn't need to independantly go in reverse. If we wanted to turn the robot, have the "engine" (motors, gearbox, transmission) power the two sets of wheels, just rotate the wheels back to the forward/backward position (a max rotation of 90 degrees) and have them spin in opposite directions.

I'd still like to have a 6 motor drive with one transmission and one gearbox though. So I figured, what if we had the engine outputting to both sets of wheels, but on one set employ the 'reverse gear'. When we're in the normal driving mode where we're swerving and whatnot, the reverse gear won't be engaged. But when we want to steer, we'll pop in the reverse gear causing the wheel sets to spin in opposite directions; and if we want to turn right, we'll run the motors foward, and instead if we want to turn left, we'll run the motors backward.

And we could use software to allow the driver to switch between conventional tank-drive and the swerve drive easily enough through this.

Laff, $@#$@#$@#$@# you Rodd! Looks similar to what I had in mind; except for the steering bit. I kind of want to avoid the whole "car" steering bit... seems like a bit much having to include differentials and whatnot.


It's a good idea to be able to just turn the wheels around 180 degrees to achieve the reverse; but wouldn't you need four motors (one for each wheel) in order to spin two of them backwards and the other two forwards?


And thanks for the wheel idea... I had something like that going around in my head, just couldn't make the parts come together properly. And after seeing that; I got a slightly different approach to it. I'll model it and put it up tonight after work.


EDIT:
Al... does that mean you can't use 6 motors ONLY when turning? Would they work fine for a swerve drive not turning? And then say when we are turning, we could just use software to make two of the motors not run during that time?

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

There are slip clutches in the differentials

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Now that i thinkabout it 4 reverse gears are not needed in my preious design if the wheel turning horizontal _ chains are run off of 2 spockets and two globes or windows or something. Instead of the M more of a X

This way you have no reverse, except for on all ofthe wheels at the same time, but you can turn the front wheels 90 degrees to the left and the back 90 degrees to the right. It wil created tank type steering and turn your front into the side, until the turn is over and the driver staightens out the wheels to dive again. There is also steering like a car, but better, cause you can turn the back wheels too, which is an option now sometime on the newer models :D .

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Would someone mind explaining to me how the power would be transfered to the wheels in a system like the ones shown here. I've been looking at a lot of the pics...and am obviously missing something, because I don't see anyway the power from the motors is getting to the wheels.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

This is just my two cents:

I would suggest staying away from the Reverse gear unless you want things to get very mechanically complex. Also, by using a reverse gear instead of changing motor direction, you cannot make point-turns, you can only counter-rotate. Think about it: Your wheels in reverse go as fast as your wheels in forward, and as far as I can understand, there would be no way to stop only one side of your bot. Personally, I would go with separate drives, but thats just my opinion.

Also, Henry_222's idea sounds cool, but:
1 drive motor + 4 module rotation motors = 5 total OR....
4 drive motors + 1 module rotation = 5 total <--- I'd go for that, more power to the floor, even if more complex.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Also..if your using the chips in the drive....there isn't a large speed difference...so for reversing...I doubt you would ever notice a difference in just going backwards.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Fizman- Not that it matters too much, but your wheels should only have to rotate 90 degrees to swerve if you run ur drive motor(s) forward and reverse

Rod- Could you explain how power is transferred from the motor to the wheels on your design, and how the wheels change direction/speed?

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

I would suggest mounting your 3 speed transmissions in the center and then have miter gears coming off that connect to the wheel modules...we were thinking of doing this but didn't have the recouses to pull it off

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

I'm curious if you could run into a situation where you have too much power. There has to be a point where you just have so much power that you can't transfer it to the carpet because the wheels are slipping. Is there any way of calculating this?

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

The senario you described wouldn't be a problem of too much power, it would be a problem of too little traction.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Well the point I was trying to make is... how much power is so much that it doesn't matter? Simply because you will run into the traction problem.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

oh, the old coaxial crab drive. a potentialaly shiftable omni drive desing sporting dashing manuverabilty

however there inavoidabaly heavy, complex. heavy, inefficent, batery hungary, recorce-eating things witch through the process of desinging my oun became Painfully apparent.

its still a wikid cool drivetrain tho

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Not ONE motor, one gearbox. Many motors potentialy. It is all in the application.

I like the ideas....but....
I see this whole venture of one power source to complicated and heavy to deal with. There are many other options.

Also,
I have only ever "peeled out" or skidded wheels on carpet once with a bot. It was a basic bottom chasis and had 6" wheels and a prototype 3 speed on the fly tranny. The wheels are the ones from the kit, Skyways I think. I flew around in 3 and slammed into 1. SKIDDDDDDDDD. And I started in 3, full stick. SKIDDDDDDDD, ZOOM. If the proper wheels are in the application, there can never be too much power. HE HE HE. :D


Ching Ching, thats my 2. On a lot of stuff.
-Henry

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Sure there can. When you start ripping up carpet, you have to much power and traction.

This does happen, and teams do get disqualified for it.

-Andy A.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

I don't know; I see the venture of one power source (while complicated) could potentially be lighter than multiple ones. I mean; even if you have to build a monster gearbox, it'd still only have to be twice the size (maybe less if you're good at compaction) than having two smaller gear boxes. Have to mount 2 motors in a gearbox? Have a gear box X size. Have to mount 4 motors in a gearbox? Have a gear box 2X size. Am I right? So the weight evens out there.

But then you can have a single transmission for the whole thing; 1/2 the pneumatics, 1/2 the mounting, 1/2 the gearing.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

With the centralized design you still have the weight of the motors. If you want to add more the a couple you have to have all the gearing to join them. If you want it to shift you can save some weight on only one but you would make up some of that on the amount of chain. Pneumatics don't weigh a lot past the first cylinder. Several of the gearshifting design use 3/4" cyclinder at a very short stroke which are very light.

What you are wanting to do is heavy by nature. With the right design and materials a centralized gearbox may be lighter. This is a tough one to call either way though. The xbox is a fairly good example of this but they said they weighed ninety pounds without shifting. And the only used to motors. More than this would require additional gearing and the gear shifting mechanism would have to be added. In this case you are looking at at around another 20+ pounds which will leave you with a 20 lb arm at most. Weight is a hard constraint to deal with. I think we would see a lot more drivetrains like you envision if we could weight 20 to 30 more pounds.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

Are you saying that:

3 motor gearbox + 3 motor gearbox +2xTransmission < 6 motor gearbox + 1xTransmission?

A central gearbox would indeed require chain and/or a shaft extending out to the other wheels, but I don't see that taking up that much extra weight. Besides; other drive systems would require the same thing to transfer the power out to the wheels.

And with the shifting, it's not just the pneumatics; it's the extra mounting, gearing, maybe another shaft. Plus if you can reduce the amount of pneumatics required to fire to shift; we might be able to ditch the need to include the air compressor.

When I compare something like this to a traditional tank drive system; I see the only extra weight coming in to support the one extra motor to turn all the wheels, and maybe the little bit more with the wheel mounts. And then the reversing gear; which would probably weight the same amount or less than the second transmission. Or perhaps better yet; maybe it can be implemented along with the transmission somehow...

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

I'm more comparing the xbox design which only utilize two motors and doesn't shift or have a reverse gear. It weighed 90 lbs. Yes I know the robot they show was a prototype and a lot of weight can be reduces out of the other materials. I thought there drivetrain in general was very nice in design. Four more motors and the gearing to join them, a multi-speed option, and a reverse gear would add weight on top of being centralized and being a swerve drive. I think a good design would be about equal to or maybe even a little less than using multiple gearboxes. I just don't see a large enough benefit for the complexities added in having both a centralized drive and centralized steering.

Re: Four Wheel, all steering, non-omniwheel, ONE power/motor source drive
 

I would look at this question from an overall robot design standpoint... If you have one huge (relatively) gearbox in the center of your robot, thats going to limit you on your ability to integrate your mechanisms into the robot, espescially an arm with a wide degree of freedom. If you do the two seperate transmissions route, you leave the entire center of your robot free for whatever you see fit. If you look around, there are a lot of evolving 'drive module' designs that have the entire drive sections of the robot all compact in thier own self supporting 5" wide (sometimes even smaller) sections on the outside of the robot. Also something to care about, having that big gearbox in the middle of the robot could require you to raise anything else that would typically go down the center of your bot and drastically raise your CoG.


If you are using steel shafts, the weight adds up extremely quickly. A full robot lenght shaft would also need to be very supported into your robot, and to have one for each set of wheels, that is a whole lot of weight. Check into the bending moment on shafts that long, and then to have it be a powered drive shaft.... you get the idea. Having just 4x 5 inch non-powered wheel supporting shafts is a big advantage in the weight saving department.


Adding a shifter into a gearbox should probably not require many extra shafts than you would normally have. Just the one shifter shaft which you will need in a unified gearbox anyway. If you are adding a lot of extra, you may want to check your gearing layout. Having 2 individual shifting pistons doesn't mean you will use a lot of air. This year on our fall drive base and competition robot we used 2 individual 1/2" throw 3/4" bore pnuematics and were about to shift about 35 times conservatively. No onbaord compressor was ever required. Even if you had 2 1" throw pistons, are you really going to be shifting that much in a single match?


On top of just added weight, thats 7 motors minimum you are looking at into just your drive. You need to remember the wonderful rules of power distribution, and make sure you have acceptable motors for the rest of your mechanisms. The turning motor will need its own gearbox also and shafts/chain to make it to all 4 wheels. A reversing gear would require another extra shaft and ultimately, more weight. Wheel support is not something you should go lightly on. I know in 2002 some teams who lifted goals ended up paying for it in the long run when thier wheels bowed outward after a few competitions.
In all, do you think the added complexity and weight are worth it? Not to mention the array of extra parts that will need to be designed and fabricated.