What type of drive train is the most maneuverable?
 

Our team has, in the past few years, had a problem with robots that cannot move around very well. While our driver has compensated for it quite well, I know she could be ten times better if our robot could move around more.

What do you think is the most maneuverable (and practical. We're on a tight budget.) drive train?

Thanks for your thoughts!
-Brittany

ps. I realize I'm programming/ electrical, but I'd like to be able to program our robot to go where it's supposed to go! :rolleyes:

Re: What type of drive train is the most maneuverable?
 

In another thread there has been some good recent discussion of a very maneuverable drive train using mecanum wheels.

A good compromise between maneuverability and defensive capability is the popular 6WD system.

Re: What type of drive train is the most maneuverable?
 

On a tight budget? I'd have to go with a 6 wheel drive train with a lowered middle wheel. There are tons of examples of it done well here on CD, just search around CD Media.

Re: What type of drive train is the most maneuverable?
 

A very simple and highly-manuverable chassis is two-wheel drive with ball casters, as used recently by 56, 103 and many others.

Pros: It is very light weight and easy to implement, has fewer components than six-wheel drive and has very low scrub (frictional) losses when changing direction.

Cons: While it can push strongly in the forward direction, it has very low pushing ability off-axis or backward (due to weight transfer off the drive wheels). This system is best-suited to a flat and level field, as it has relatively poor drive dynamics when sideways on a sloped surface, such as a ramp, and would probably have a really tough time on steps!

Stay away from swivel casters, as they steer the robot in the direction they're turned towards - which often seems to be the wrong way!

Re: What type of drive train is the most maneuverable?
 

A well designed 6 or 4 wheel drive system has always had the best ratio of pros to cons in my opinion.

http://www.chiefdelphi.com/media/papers/1443

That paper should show you how to get it set up correctly.

Re: What type of drive train is the most maneuverable?
 

While mecanum provides a nice balance of maneuverability with traction, the wheels themselves are fairly complicated, fragile, and can be expensive to machine/purchase. A two drive wheel two caster design is cheap in comparison and still provides great maneuverability. We chose the two caster design for our bot this past year.

Re: What type of drive train is the most maneuverable?
 

another drive is the holonomic drive. It uses 3/4 wheels mounted 120/90 degrees apart. It is very maneuverable, but can be easy to push.

Vex Holonomic(the 8th post in this thread has the code needed to drive the robot) http://www.chiefdelphi.com/forums/sh...ad.php?t=46560
3 wheel vs. 4 wheel http://www.chiefdelphi.com/forums/sh...ight=holonomic
advantages of holonomic http://www.chiefdelphi.com/forums/sh...ight=holonomic
The math involved in driving a holonomic http://www.chiefdelphi.com/forums/sh...984#post354984

Re: What type of drive train is the most maneuverable?
 

What have you done in past years. We usually do a 4 wheel skid steer drive type and have not had many problems with maneuverability. We usually do some grippy wheels in the back and some less grippy wheels in the front to reduce scrub when turning.

Kiwi and Mencanum seem very complicated to me if you are a lower budget team and unless you have access to a machine shop (and have people who know how to use it) i wouldnt recommend them to a team on a tight budget.

Re: What type of drive train is the most maneuverable?
 

team 294 has used a very simple solution the past two years.

Kit transmissions to 6 skyway wheels, the center wheels were treaded with waffle tread and lowered. We didn't have the best traction or turning ability, but we turned well and could push decently. Also, we were able to finish the base assembly in a day.

Re: What type of drive train is the most maneuverable?
 

Team 118 used a crab drive, drive train. A crab drive lets all four wheels move together. So if you want to go left, your robot is still facing forward, but your wheels all turnto the left. It is THE most manuverable because it lets you get anywhere in a short amount of time because instead of wasting time turning your robot around, all you do is move the wheels and that made this previous years game easy because we could score while moving from one side of the field to another.

This what our wheel box looked like for our practice bot,


and this is what all four of them looked like.

Re: What type of drive train is the most maneuverable?
 

In terms of pure maneuverability, mecanum is the best, as it can travel in any planar direction, change direction almost instantly, and can conquer inclines easier than a holonomic drive. Holonomic and ball drives can also travel in any planar direction and change direction almost instantly. Swerve drives can also travel in any planar direction, but they recquire time (often very small though) to change the orientation of their wheels. "Crab drives" (a variant of swerve drives where all the wheels are linked together) are the simplest swerve drive, but recquire more power (as the have to overcome more scrub) to move in curves. Afterwards comes the plethora of different scrub (tank/skid) steer systems.
4WD, 6WD, 2WD (and 2WD+caster), and many others all fall into this category. While some may recommend the caster system, I would advise against it. From my personal preferance, while quite maneuvable, the lack of control on the casters can cause more problems that it solves. It significantly reduces your control over your bot, and therefor reduces the amount of accuracy you can drive with. Momentum can often cause the rear end (assuming your casters are in your rear) of your bot to swing further than you want it to. It also makes you a relatively easy target to push (and incredibly easy to rotate out of position).
The "best buy" for maneuverability (in my opinion) would be a 4WD with 2 omni-wheels.

Re: What type of drive train is the most maneuverable?
 

I definently agree with Lil' Lavery- The best bang for the buck if you're not concerned with lots of defence or complication will be the four wheel setup and omni's out front.

Six wheel is another excellent choice with a lowered center wheel- but it also requires more time, complication, and weight budget. However, it's nearly impossible to be spun sideways, or lose traction on inclines, bumpy ground, etc.


Mechanum and swerve are very impressive and capable designs when the game warrants them, but compared to standard drive-trains, a huge amount of design and fabrication muscle needs to go into them.

Re: What type of drive train is the most maneuverable?
 

The center wheel doesn't always have to be lowered. Team 25 has been using a 6WD design for many years, and we have never had to lower our center wheel.

Re: What type of drive train is the most maneuverable?
 

I actually prefer omni's on opposite corners (like 494/70) as opposed to 2 on the same side. That way it makes you harder to be spun by other teams, but still allows you to spin and change direction quickly and accurately.

Re: What type of drive train is the most maneuverable?
 

That is an awesome idea...

Re: What type of drive train is the most maneuverable?
 

Yes it is. And effective. Recall this rather intimidating scene?

Re: What type of drive train is the most maneuverable?
 

in the idea of a slim budget, the omnis are about $80 for 2.....extra skyways that can easily be set up with the kit drive train are much cheaper. if you have the extra money the 4wd with omnis are a good option, but if you don't have the cash or would rather save it for another area id stay with kit 6wd drive with the lowered middle wheel and I know 25 doesn't lower their middle wheel which is fine, but the kit bot is already setup for it.....

Re: What type of drive train is the most maneuverable?
 

I think the simplicity and low energy requirements of a 2 wheel drive system are being overlooked:

1. with a 2 wheel drive system you dont have to scrub any wheels to turn. It takes very little power to steer

2. instead of using castors, you can use low friction material and have skid plates on the corners. Anyone who has ever pushed a shopping cart knows castors take some force to get them to point in the direction you want them to go. The result is the force required to turn is non-linear until the castor rotates. A skid plate solves this problem, or you could use a ball style castor (its like a big ball bearing that is free to rotate in any direction.

3. You can compensate for the 'being pushed sideways' and 'hard to steer up a ramp' issue very simply, using the yaw rate sensor (gyro chip) that has been in the KOP, and using a simple feedback loop to close the loop on the steering. Then you have the best of both worlds, a robot that will spin on a dime, taking very little energy to do so, and that will use all of its available motor power to keep pointing in the direction the joystick is commanding, no matter who or what (gravity) is trying to make it turn.

Re: What type of drive train is the most maneuverable?
 

i think we're all over looking the hovercraft... ( :p )

For a really tight budget, that would probably rule out crab, mecanum, or omni (spending money on wheels and the drivetrain might not be most well spend, depending on the game)

Probably one of the easiest (and cheapest) to impliment would be the 2 wheel / skid plates.
!*caution*! with the gyro, make sure its rated to a high rotation, when we tried to use that with our robot this year, it messed up because it could only do 80 degrees/sec !/*caution*/!

I would say experiment as much as you can in the off-season, build a generic frame, and try different configurations with the wheels, OR browse soap's collection of matches, and take a peak at each of the videos.

Re: What type of drive train is the most maneuverable?
 

I personally can reccomend the swerve system, as 114 had great fun with one of those. The only issue is how to program the thing, and still have it driveable.

As far as most cost effective and still maneuverable, a 6 wheel with the middle wheel lowered is pretty nice.

Re: What type of drive train is the most maneuverable?
 

mecanum and holonomic are very maneuverable, but they only have on average at best 70% efficiency. And they're arguably more complicated to program, needs sensors, etc.

swerve is a complicated system of wheel modules and takes time and money to fabricate, but is more efficient (more pushing power) than mecanum/holonomic. Still has a bit of programming to do, and sensors. swerve can also get heavy if weight isnt seriously taken into consideration during design.

6 wheel drive is simpler to fabricate, cheaper, and easy to program. however, you cant strafe sideways. you can turn arguably better than most other drives, but your robot will rock back and forth a little, which isnt always good.

personally, I'd go with 2 speed swerve. all you guys that think its too hard to pull off, too heavy, too expensive, too complicated, or overkill can have their opinions.

Re: What type of drive train is the most maneuverable?
 

I guess you want to have your cake and eat it too!

Some words of advice.. Don't try to do too much! If you want to be agile and escape defenders, then do it. If you want to push defenders out of the way, the n do it. Don't try to switch up mid match as it will only cause you to waste valuable time.

The smartest thing you can do is analyze the game when it comes out and devise a strategy to your liking. Base your design goals off of this, and seriously consider what each available setup can add to your overall design.

Re: What type of drive train is the most maneuverable?
 

Agreed!
Ball casters solve this problem nicely (McMaster-Carr #2364T1).

If you go with these parts, be sure to reinforce the mount - the stud mount sees a bunch of stress and breaks easily if you run into something.

Re: What type of drive train is the most maneuverable?
 

I think there are three vesions of the Analog Devices solid state gyro (yaw rate sensor) with different max turn rates, with the highest being 300°/S.

The faster sensor lets you spin your bot quicker with the loop closed, and it will stay 'locked' if your bot is hit, or hits something, and spins at a rate below 300°/S - but neither of these things are show stoppers.

the slowest sensor: 80° / S is a fast enough turn rate for normal driving. If you are spinning your robot 360°/ Second, you are not driving, you are doing a victory spin!

Two things: when the sensor is turned faster than its max rate, it outputs the full scale reading - your control loop will continue to respond with its max output, so the robot does not go berzerk, it acts predictably.

The only shortfall is if you are integrating the sensor to get compass heading, the reading will be wrong if the robot is spun too fast (by an external force). In this case you need a way to reset the heading (if the sensor is being used that way) during a match.

2. If you close the loop on steering with a gryo sensor, I recommend you have a disable switch on the control panel. That way you can drive with the loop closed, giving you very precise steering, and the robot will fight on its on to hold its heading (when something external tries to push it sideways), and then if you want to drive the robot open-loop (victory spins and stuff) you can, with the flip of the switch.

yes, and ball castors or skid plates take up very little space, which means, you could also have pnuematic feet that extend down, with high friction plates, that can be deployed when you want your robot to stay where you parked it!.

Re: What type of drive train is the most maneuverable?
 

We have used those in the past and fount that the 4" version #2364T2 work better.


And I agree that 2 wheel drive (75-80% weight over the drive wheels) and 2 ball casters gives the best manuverability for the dollar.

And when you want to 'stay in place' either drop a skid plate (anchor) or raise the ball casters with a cylinder or leadscrew.

Re: What type of drive train is the most maneuverable?
 

Nice ideas! Personally I'm in love with the holonomic (4-wheel kiwi) drive train for maneuverability and cost... However the diagonally mounted omni/traction wheel is an excellent idea in my opinion (if you don't want to move sideways)! I just think that maneuverability is increased dramatically when you ad another degree of freedom!

Now, for the complaint about holonomics not being able to go up ramps, I think you have a good point in that it's relatively hard, but definitely essayer to maneuver once on the ramp! I believe I can speak about this as the driver of a 4-wheel drive all-sky wheel drive train in the '06 competition. Once I got on the ramp (really easy) I could hardly move along it, it was something to do with the insane difference between driving on a level ground, and having one wheel atop the ramp providing bookoo friction against a turn... Now for a kiwi drive friction may be the deciding factor regarding your movement at all on said metal ramp, but you could definitely provide force in any direction you choose!

But for overall simplicity of design, and a good two degree of freedom drive train ideal for getting around your opponents... I'd pick the diagonally mounted omni/traction, because your not a rookie team, and you can probably handle it!

Re: What type of drive train is the most maneuverable?
 

Wow, I posted yesterday, and there's already fifty million posts! This is awesome, I love Chief Delphi :p .

Another question: For a defensive type robot that is still maneuverable, what do you think is the best? (For our sadly depleted bank account :( )

(I'll probably be asking a lot of different questions. I have no idea what our robot will be doing this year.)

Thanks for your thoughts!

-Brittany

Re: What type of drive train is the most maneuverable?
 

If you want the best capability, 6 wheel is the way to go, in my opinion. You may use a long-style frame orientation (more suitable for pushing), and six wheel gives you a great number of wheels on the ground without sacrificing manueverability.

*Note- More wheels does not typically mean more traction. It's simply advantageous to have more wheels because when on obstacles or being shoved around, it's more likely that you'll have a wheel on the ground, and less likely you'll bottom out.

Re: What type of drive train is the most maneuverable?
 

Either a 6 wheel drive with the kitbot, or the alternating omini & traction wheels.

Re: What type of drive train is the most maneuverable?
 

I would totaly agree that a 6-wheel drive system would be ideal, a 4-wheel system would work but would not be as mobile. This all really depends on how low your center-of-gravity (CoG) is. If you are focusing on a defensive robot it should have a very low CoG and most drive systems will turn well. Try and get your hands on some traction wheels, look at ifi, and if you are willing to spend the cash grab some andymark 2-speed servo-shifting :yikes: gearbox's would be a very nice addition. Have a look at a team like 1305 from this year for a sweet 6-wheel drive system.

Re: What type of drive train is the most maneuverable?
 

A look at 610 from this year would be worthwhile, too. Very nice use of 6WD and grippy stuff on the wheels.

Re: What type of drive train is the most maneuverable?
 

For a defensive/offensive combo, Swerve would be the cream of the crop, but also expensive. The "best buy" for an agile defender would probably be a 6WD.

Re: What type of drive train is the most maneuverable?
 

Our programmers this year actually got the code down to 4 lines... and it was just converting joy numbers to good PWM values.... super efficient.

Most programmers that I've met actually say they're easier to program than a 4-wheel / 6 wheel tank drive, or at least the ones that have used them.
Only a very weird configuration would make it harder... like only using 3 wheels :p

As for making it go relative to the driver, thats where it becomes tricky (all that great vector math). Thats where we used the gyro, and thats how our robot messed up (preseason, the lead programmer then decided that it wasn't worth our time).

We also found out that a gyro is affected by temperature, pressure, etc. greatly; and that it gave out different readings at different times of the day :( oh well

Re: What type of drive train is the most maneuverable?
 

How would vectors not apply for robot-centric control as well? :confused:

Re: What type of drive train is the most maneuverable?
 

I'm simple. I am a fan of the 4w tank drive, for several years we always went with a width ways orientation so we had a zero degress turning radius. but this last year we had a 4 wheel 2 spd tank that was long ways so to solve the manuverablility problem we implemented a pop-castor design that used a piston to push up the fron and turn on 2 castors and the rear wheels. It looks pretty sweet too!!!

Re: What type of drive train is the most maneuverable?
 

the vector math is easier, and actually is just converting joy input to PWM values (4 lines of code)...

In a stroke of brilliance one of our programmers got rid of all the vectors... and explained "To go left, turn these wheels forward, those ones backward. To go right, turn these wheels backward, those ones forward. To go forward, all wheels go forward, backwards the same. To spin, turn these 2 forward, these 2 backward, and vice-versa" (as he pointed to our diagram).

now (like all other drives) the driver is thinking in terms of the robot, so they're the ones "doing the math".
The robot isn't remembering where it is, so theres fewer vectors involved.

If the robot did remember where it was, the coding would become absolutely atrocious.

Re: What type of drive train is the most maneuverable?
 

if that was true then your gyro was defective or there was a bug in your code reading the gryo value. Solid state gyros are highly reliable, the same AD chips used on the robots are used in cars for things like airbags and stability control (steering).

One thing about the gyros, they must be solidly mounted to the chassis of the robot. If the gyro can wiggle and vibrate (if you hold it down with tie wraps, or foam tape) you will get all sorts junk on the output signal.

To be useful the gyro chip must move exactly the same as the robot chassis moves.

Re: What type of drive train is the most maneuverable?
 

Our 2006 Martian robots were initially designed and built with the same knobby pneumatic skid steer drive train layout we had in 2003,4, and 5. This proved to be too unstable during turning because of the robots’ higher center of gravity. The diagonally placed omni wheels were installed very late in the build. Omni wheels are fine for maneuverability, but not good for resisting a lateral push.

If we had it to do over again, we would have had a drive train very similar to what 469 did this year (and what we did in 2001 on our first Martian robot). Las Gorillas had a skid steer with a set of deployable ball casters on the front right and left to lift the front of the robot off of the ground for maneuverability. When the casters were retracted, all four knobby pneumatic tires were on the ground for impressive pushing power and sideways stability against an aggressor.

Re: What type of drive train is the most maneuverable?
 

What are the joystick controls you use? I can see that the robot can slew around very easily, but what if you really do want to face the robot to a different heading?

Re: What type of drive train is the most maneuverable?
 

When HOT did crab in 2005, we used a regular black Flightstick (forward, backward, left strafe, right strafe) and a Playstation steering wheel to change the robot's orientation.
We just opened up the case of the steering wheel and soldered some wires onto the potentiometer to put into a gameport connector.

Re: What type of drive train is the most maneuverable?
 

Although swerve drive can maneuver around objects, it is not the most physical of drive trains. From what I've seen, the most effective drive seems to be the 6WD.

Re: What type of drive train is the most maneuverable?
 

MORT's best drive train was a 4-wheel.
It used 5" (I think, I'm sure Brandon can correct me) Colson wheels with a very short, wide wheelbase (long robot, short wheelbase) to cut down on scrub. The tipping problems of a short wheelbase were solved with 4 ball casters, one on each corner. It handled beautifully, could get up some decent speed, and was a pretty vicious defender. (I'm pretty sure that robot provoked the no-wedge rule.) Keep in mind however, that this was a flatland drive train for triple-play.
General suggestions based on that bot:
*Colsons rock
*Find the happy balance in the ratio or use a 2speed tranny. (I don't remember what our ratio was.)
*Short, wide wheelbase reduces scrub.
*Ball casters are beautiful on flat land.
*Keep the game in mind. A flat game needs no clearance, a ramp does.

Re: What type of drive train is the most maneuverable?
 

Just an off topic post. If you want manuverable go with a wide robot. Doesn't matter how many wheels you have, it will still be better than a long robot.

Re: What type of drive train is the most maneuverable?
 

All other things being equal, a typical six wheel drive along the long axis will have a shorter effective wheelbase than a four wheel drive arranged on the short axis.

Re: What type of drive train is the most maneuverable?
 

Is there a way to calculate the force (or torque, whatever) required to have a robot turn?

Re: What type of drive train is the most maneuverable?
 

Re: What type of drive train is the most maneuverable?
 

Uhhhmmmmm, not so fast there. As a general statement, this is not true.

It all depends on how you are going to define a "typical six wheel drive" and what assumptions and caveats you are putting on that definition. I will maintain that in a "typical" six-wheel drive, all six wheels are co-planar. In that case, the wheelbase of the six-wheel drive is established by the Conservative Support Polygon, which is defined by the four outer wheels. As specified in the original statement, the wheels are arranged along the long axis of the robot. The four outer wheels determine the resulting wheelbase, which by definition is longer than a four-wheel drive arranged along the short axis of the robot.

This fundamental truism is only modified if the definition of a "typical" six-wheel drive is altered to promote non-standard configurations. For example, the common practice of moving the middle pair of wheels into a non-planar configuration. On a hard planar surface, this causes the robot to ride on the middle set of wheels and one of the "end" set of wheels. Only four wheels support the robot, not six. Thus, the wheelbase becomes approximately half of the long dimension of the robot. But this is actually no longer a true six-wheel mobility system. It is a set of two four-wheel systems that share a common pair of wheels (the center ones). In this case, you lose many of the advantages of a six-wheel drive (ie. distribution of weight across more points of contact with the floor, greater stability across the longer wheelbase, etc.).

-dave

Re: What type of drive train is the most maneuverable?
 

Yes, this is entirely true -- and what I get for posting at 3 AM or some ungodly hour like that. In FIRST, I consider a 'typical' 6WD arrangement to include a lowered center wheel, but I can see that in another application, this definition would be incorrect. Trucks or airplanes, for example, may ride on six wheels rather four to, as you mention, better distribute their weight across a surface. I meant to speak only with the confines of FIRST use -- and even then, perhaps it's erroneous to assume that most consider the 'typical' 6WD arrangement to have a lowered center wheel.

Re: What type of drive train is the most maneuverable?
 

I remember looking at that whitepaper. I recall that the only thing it said was that the length of the robot should be less that the wheelbase, for the robot to just begin to turn. I will look again to see if there is a method to determine how much force is required by a certain dimensioned robot, with a certain weight and a certain CoF with the carpet, to turn.

[edit: Ok, the equation is there. Great.]

Re: What type of drive train is the most maneuverable?
 

All you students out there, read the post above, at least twice. There is a great lesson in it.

Many of the references (books, articles, poems, CD threads, etc.) that you will encounter will have more to say to you when you re-read them a season or two later. The reference doesn't change from one reading to the next, but you do. And you get smarter, or more experienced, or both.

Re: What type of drive train is the most maneuverable?
 

I have read this white paper twice and I believe there is another factor to consider. The effective coefficient of friction in the lateral direction of a stationary tire is different (higher) than a tire that is slipping on the carpet.

We have had several successful skid steer robots with the wheelbase greater than the track width. These robots had large knobby pneumatic tires that were quite sticky. If the driver attempted to turn by energizing only the right side wheels and keep the left side stationary, the robot would not turn, as the white paper would suggest. If the operator pushed one stick forward and the other rearward with enough power to break the tires loose, the robot would turn. This was not a graceful turn, but worked well. This method requires the robot to have enough torque to break all wheels loose on carpet at the same time.

There is a good way to visualize this if you have ever driven on an icy road with a rear wheel drive vehicle. If you punch the accelerator and break the tires loose, the rear of the vehicle will move sideways as it slides down the crown of the road.

I cannot offer a formula to show this at this time, so I will have to leave the proof as an exercise for the reader.

Jay

Re: What type of drive train is the most maneuverable?
 

Re: What type of drive train is the most maneuverable?
 

The drive train that the students came up with a couple of years ago is a pretty good system. We have used it in OCCRA for 2 years now and for the altering of our FIRST robots, which is four wheel drive in the back with casters or skyway wheels in the front. We also tried slides in the front instead of casters but I like the casters better. It is a simple machine for your budget and is very dependable. :)

Re: What type of drive train is the most maneuverable?
 

Ours was similar. The 4WD part had perhaps a 15 inch wheelbase and we used poly skids at the other end. Even so, the pneumatic tires were so grippy that steering was a bit herky jerky. Good system, though. Simple and reliable. he team won the Motorola Qualiity Award at the VCU regional for the overall 'bot.

Re: What type of drive train is the most maneuverable?
 

I just did this yesterday for our test plateform. Just be careful about how much u lower the middle wheel. We used 3mm and it works great in carpet.