omni drive vs tank
 

which kind of mobility is every1 thinking of. a good idea that came up today while we were brainstorming was a tank mobility any other ideas??

Re: omni drive vs tank
 

tank treads are WAYYYYY too slow for this game. you gotta go with 4 wheel tank drive. relatively good speed and good push power and easy to do, especially for a rookie team.

Re: omni drive vs tank
 

Typical answer but not always the truth. You can get high speeds with treads if you have the proper gear ratio. I recall team 61 (i think) moving with great speeds in 04 competition and team 180's old tread system to be very powerful. But be sure to do the engineering before the season starts, or you might run out of time like our team did in 03 and had some serious engineering flaws that we found out on the first day of competition.

We are going 6x6 for this years game....

Re: omni drive vs tank
 

ya, i agree, but if its your rookie year treads are too complicated. lots to go wrong, shreading treads, loss of limbs, lots of moving parts(if one fails all the rest can). i mean its just best to keep it simple for your first year, dont go for the gold right away, learn it, then conquer it.

Re: omni drive vs tank
 

Just like last year, team 1318 is going to use a 6-wheel drive system. It worked well then, it should work well now.

However, this year we'll probably use pneumatic tires to get more tread on the diamond plating, instead of the kitbot ones like last year.

Re: omni drive vs tank
 

You'll want to consider that very, very carefully.

Re: omni drive vs tank
 

we were thinking of using a diamond shaped base with a tank drive that would be centered in the middle of the diamond. this way it'd be harder for people to push us because to get maximum area they would have to hit a slanted side which we could still keep driving forward than, however first my frown on the idea that the corner would be in the front of our robot and thus creating a spear like robot

Re: omni drive vs tank
 

You can't make diamond shaped sides anymore, they have to be within 10 degrees of vertical as the rules state here

<R04> "Wedge” robots are not allowed. Robots must be designed so that interaction with other robots results in
pushing rather than tipping or lifting. Neither offensive nor defensive wedges are allowed. All parts of a
robot between 0 and 8.5 inches from the ground (the top of the bumper zone – see Rule <R35>) that might
push against another robot must be within 10 degrees of vertical. Devices deployed outside the robot's
footprint should be designed to avoid wedging. If a mechanism or an appendage (a ball harvester, for
example) becomes a wedge that interferes with other robots, penalties, disabling, or disqualification can occur
depending on the severity of the infraction.

Re: omni drive vs tank
 

I believe that the rule is refereeing to the sides of your robot. So that you cannot tip another bot. I do not believe that there is any restriction to the actual shape the bot looking down at it. I dont know if that made any sense to any of you all but it did to me....

Re: omni drive vs tank
 

it all depends on your robot and what roles you want to play on the field. A holonomic or mechanum drive system is going to have problems with the ramp unless you create some sort of suspension, although they will be the most agile and mobile in the open field.
A tank drive will have tons of traction, and be awesome for the ramp/platform, but it may not possess the maneuverability to an omni-drive in certain situations in the open field, or chase bouncing balls.
Swerve drive may be a nice solution to these problems, but those can be fairly hard to build.

There are many many other factors that tie into this, what kind of ball shooting are you employing, will you shoot on the move, will you shoot at all, etc etc etc

Re: omni drive vs tank
 

This game needs both speed and power. So you need to come up with a drive system that maximizes both. though accuracy is needed somewhat if your planning on manually aiming to shoot.

Re: omni drive vs tank
 

Our team, 1257 had a fully fuctional holonomic drive last year. It was quickly decided that its not a good choice for this game. Defensivly, the only thing to do other then stand in front of the lower goal is to ram like hell, and you just dont get any traction with the omniwheels. Also lets just say there isnt a chance in hell of a holonomic drivetrain making it up that ramp.

Re: omni drive vs tank
 

do you need me to show you video's? they are not slow so don't say they are.. I will show you video's of how fast and how POWERFULL they are

2004 Mayhem on the Merrimack Fastest Robot Award!

But remember tank treads are slow... Time for you to get your facts straight :(

Yes.. Just look at my signature.. Won a lot of compitions this year..

Re: omni drive vs tank
 

tank treads are def not slow, but honestly there is no need for them in this years game. Theres no terrian obstacles other then the 30 degree ramp which shouldnt be a problem to get up. i would go 6 wheel drive and just chain the wheels

Re: omni drive vs tank
 

defense? yeah that's why you need them to push other robots around from scoring.

Re: omni drive vs tank
 

ya you get just as much traction with the pneumatic wheels with those big CIMs it wont be necessary to use tank treads and if any team is smart they will use a pneumatic brakepad system to hold their ground while shooting at the center goal

Re: omni drive vs tank
 

I'll bite. This year's game will not be friendly to omni wheel drives (unless you can shoot extremely accurately on the fly). It will also not be friendly to tank treads, although I am not sure that is what you meant. Tank does not mean tank treads you guys. It could mean a skid steer system, which would be good, unless you want to go ramp climbing. Although after last year and 116's incredibly wicked sweet drive, I'm sure you can think of something cool.

Re: omni drive vs tank
 

Im not saying it wont be friendly to tank treads im just saying it wont be neccessary your better off going witha 6 wheel pneumatic tire drive train, that ramp isnt going to be to hard to get on. other then that its all about speed, traction, and movability. A functional holonomic drive train is fast as h*** and nice manevability if you practicle driveing but if u get pushed you got zero traction, we even replaced the wheels and added tire treds we literally glued on with some industrial glue the traction increased but if you get pushed you slide.

Re: omni drive vs tank
 

it is possible for a crab drive or an omni drive to get up the ramp with the help of another robot. There will be plenty of tankbots that can push them ramp, just make those wheel/motor assemblies strong.

Re: omni drive vs tank
 

I think a crab could get up in its own but an omni would need the assistance of a dropdown high traction roller of some sort.

I think a crab is perfect for the game, but I don't think my team wants to go that way.

Re: omni drive vs tank
 

Omni wheel drives, when not being useful while climbing the ramp, will probably prove to be extremely valuable when a team is positioning itself to shoot the balls into the corner goal. Lets say you have positioned your robot in front of the goal to shoot and you find yourself a little too far left. Without Omni wheels its given that u will turn right, go forward a little and turn left again to face the goal. Precious time lost...which wont be if you use an omni drive system.

My team has used a four wheel drive system with doubled up wheels wrapped in tread(from McMaster Carr) and two pneumatically activated castor wheels. If all four wheels are on the floor the robot has a LOT of traction and works well as a defensive robot. If the castors are actuated and pushes the front wheels up, it gives it the manuevarability required in the FIRST games. We have found this to work quite well.

On the topic on tank drives, it is a very hard thing to perfectly execute. Tank drives require a lot of work and the result is not very much advantageous over a normal four wheel drive system.

These are just my thoughts. The game dynamics on the field will also have a great say on the reliability and advantages of each of these different systems.

Good Luck

Re: omni drive vs tank
 

Omni bots will have a place in this year's game, although I dont know if 116 will use a holonomic drive again. More advanced programming teams may like omni-drives to "shoot on the fly", especially if they dont develope a turret system for their launcher. Agility and speed will be essential in reaching the corner goals/HP stations, because you CANNOT power your way to them (youll just jam the opponent into the corner, and its gonna be near impossible to get them out).
It is POSSIBLE to create an active suspension system, although very difficult, for a holonomic or mechanum drive to get up the ramp.

Re: omni drive vs tank
 

if it werent our "first" year doing this we would push for omni or crab drive... and it would be nice if the "shooter" were ALWAYS pointed at the goal. no matter which way the joystick is puished the robot moves int the x/y accordingly but the programming keeps the front faced towards the goal.
i guess a rotating top would do as well

Re: omni drive vs tank
 

regarding the tank treads- it's not so much that they're slow, it's that they're not good for turning, which will probably end up being an important part of this game.

Re: omni drive vs tank
 

That was the first thing that I thought of once I saw that green light. Set the camera to home in on the light and rotate the firing mechanism.

I'm pretty sure that team 648 is going with a crab steer system and that is the perfect drive system for that design idea. This will also be our first year for crab but we have been testing design and coding on the Robovation bot.

Re: omni drive vs tank
 

if you do it correctly, they can turn just as easily as a tank drive.

Re: omni drive vs tank
 

The thing about tracks is that I haven't seen proof that you can get more traction with them than with a good treaded wheel. And unless you are climbing a stair, I haven't seen a good reason for why you need them. And there are a few excellent reasons not to have them.

Re: omni drive vs tank
 

sounds like a good offseason project to me. Make two identically geared drives, make one with treads, one with wheels using the same belt material. See which pushes the other.

Even if it turns out treads aren't better...you'll know how to use them for the future. And you can teach new kids a bunch about drivetrains. :)

Re: omni drive vs tank
 

I made a 1min video on the Speed, Power and Traction of tank treads..


Introducing: Speed, Power and Traction of Tank Treads

I made a 1min turning video

EDIT: Introdicing: Sooo Tracks Can't Turn?

Re: omni drive vs tank
 

bump

Re: omni drive vs tank
 

hey billy goats...do you think you could show me those videos??? i'm on a second year team and we were looking at tank treads, could you tell me where i could find those???

Re: omni drive vs tank
 

Tank treads would be profitable if you can get the gear ratio adjusted so that its fast enough to keep up. Problem is, the biggest advantage of having treads is their grip and strength on the carpet. So gearing it for speed would lose the power aspect of having treads.

Re: omni drive vs tank
 

If you look at the video you will see how fast we run at. we would be one of the fastest robot on the floor. but with the most power. you are right you have to get the gearing right. we always used 4 motors for the drivetrain.


how fast do you want to go. to fast and you have no control. Now with multi gear shifting we have all we need. :)

Re: omni drive vs tank
 

Our team usually goes with 4 wheel drive tank style. We have thought about Omni Drive, but it turned out that we want maneuverability. Tank Drive is the best..

Re: omni drive vs tank
 

????? :confused:
Wouldn't omni-drive type systems give a far greater maneuverability?

Re: omni drive vs tank
 

tank drive is extremely maneurerable when done correctly. I think it is better than omni wheels becuase part of my definition of maneuverability is ease of getting it to the specific spot, well omni wheels get thrown around to easily.

just some thoughts

Re: omni drive vs tank
 

I would say tank because i see alot of pushing going on

Re: omni drive vs tank
 

The major problem I see with omni's is stability. Depending on your strategy, you might want to stay in a fixed location to shoot balls. However, Even given that you can try and stay fixed with omni's I think that you wil find your robot being bumped all day.

Just an opion though.

Re: omni drive vs tank
 

obviously. But you don't get the power that tracks get you

Re: omni drive vs tank
 

See video/thread/link below.

See note on above quote.



2005 Team195 Tank Tread Drive System+ 4 speed transmission

Guys, seriously this thread is pretty much out of control. None of you really outline good reasons why a tank drive system is not effective. The video shows a tank system being very effective in maneuverability.

Re: omni drive vs tank
 

That's because it is much easier to spout worthless generalities and platitudes than to provide an argument of any substance.

As people learn more and mature (especially as engineers) they learn that in a technical discussion phrases similar to "Never use tank treads, they can't turn." aren't worth reading.

$.02
-JV

Re: omni drive vs tank
 

Having said all that, I'll get off the soapbox and describe some of the actual physical phenomena that are being loosely described in this thread.

Robot Myth Busters - Linear Pushing Force:

Myth: Tank Treads have a significantly greater pushing force than Omni drives.

Math:
In actuality, pushing force is dependant on 2 things:
1. Traction
2. Torque

If you have lots of traction, but not enough torque, you stall your motors and/or blow your breakers.

If you have lots of torque, but no traction, you spin your wheels and can't push anyone.

The trick to designing a super-powerful pushing robot is do get as much traction as possible, then gearing your robot so that when it is under load (in a pushing match), the motors only draw 40 amps each.

Traction is dependant on:
a. Robot Weight
b. Wheel Coefficient of Friction

So your first step, is to maximize the robot weight. This is relatively easy in a game where the robots have a maximum allowed weight, and there are no heavy goals to lift up on (Refer to 2002, where teams increased pushing force by lifting 190 lb goals).

You then need to find a grippy tread. Most teams have comparable wheel-treads. The 'best' stuff is arguably the brecoflex stuff that many teams use.

Using wider wheels/tracks won't get you more pushing power, but it will distribute the load over a greater area; this means you won't burn holes in the carpet as easily, and it will take longer for your treads to wear down.

If you've *maxed* out your pushing power, now you need to figure out your gearing (to ensure you have enough torque). As I said briefly above, the main requirement for low-gear is: "Can push against a wall, without popping your breaker?" (We use pushing against the wall, as the worst-case load scenario).

What does this mean?
Two Robots both weigh the same. One robot has tank-treads, one robot has omni-wheels. Both are geared such that their wheels slip, and their motors only draw 40 amps during "wall push". Their CG is in relatively the same place. Who will win in a pushing contest?

Neither! They will stalemate.

Reality:
It is extremely difficult to get omni-wheels with a coefficient of friction equal to the brecoflex treads. So this scenario doesn't usually happen. However, it very easily could given the right design.

Followup:
Are you sure that the surface area of the tank-treads doesn't result in a greater coefficient of friction?

No. This is true for "ideal surfaces" only. In actuality, the surfaces aren't "perfectly flat, and smooth". This results in an interlocking matrix of materials (think velcro, on a smaller scale). In this case, the surface area does play a small effect. (This is measurable.)

However-- You can calculate an "overall coefficient of friction" for a given robot configuration. This is done with a simple pull test. Based on this, it would be possible to find an omni-wheel drive which has a comprable coefficient of friction to a tank-tread drive. So the above theory of a stalemate is still valid. Again-- the difficulty comes in finding such a system.

Overall:
Robots with traction wheels, will in most cases, win pushing matches against omni-drives. When someone invents a better omni-wheel; traction wheeled robots beware!

Re: omni drive vs tank
 

Having said all that, I'll get off the soapbox and describe some of the actual physical phenomena that are being loosely described in this thread.

Robot Myth Busters - Robot Turning:

Myth: Tank Tread Drives can't turn.

Math:
Read this whitepaper:
http://www.chiefdelphi.com/forums/pa...le&paperid=222

It is possible to design a tank-tread robotto spin on a dime. It is all based on the turning scrub of the drivetrain-wheelbase configuration, and the robot gearing.

Reality:
Using a reduced length-wheel base, (wide-body, or dropped-middle system) it is possible to create a spinning tank-tread bot. However, this may result in other negative factors such as the robot rocking back and forth between front and rear.

Overall:
Tank-treaded robots can be made to turn; however the nature of their design results in significant scrub, which must be overcome in some way.

Re: omni drive vs tank
 

Design is all about tradeoffs and compromise.
Understanding the physics and reality of each configuration is important; taking this reality and determining what is most important to construct the overall robot system is critical.

Isn't engineering fun? :)

-JV

Re: omni drive vs tank
 

Like John, I'm going to try to add some useful information to this thread so we can all speak the same language.

There is actually some truth to this statement.

Using a 4 wheel drive, tank steer machine without omni-wheels can cause a great deal of difficulty turning, so it's common practice to use omni-directional wheels, either in the front or the back (or occasionally front and back) of your machine.

The difficulty in turning occurs because you're trying to essentially slide your wheels in directions they do not want to turn. By adding omni wheels in the front, for instance, these wheels will slide (much more easily) in the lateral direction while you are turning, which reduces current draw and provides a much smoother motion.

However, to get back to the quote, one potential downside is that these omni wheels are ALWAYS easy to slide, and in the case of being bumped (from the side, near the front for example) you can expect your machine to be rotated more easily from side hits than otherwise. This becomes especially apparent when you use 4 omni-wheels on your machine - there's very little to stop you from being pushed all the way across the field when you are hit from the side.

That's my 2 cents. *Plink Plink*

Matt

Re: omni drive vs tank
 

Sometimes. But it caused me to grey a bit earlier than I wanted. :ahh:

Matt

Re: omni drive vs tank
 

For the second consecutive year we've decided to use omnis in the front and traction in the back but the omnis are run on the same chain as the traction so we get some power with them.

Re: omni drive vs tank
 

Cristian, thanks for contributing to this thread. However, I think that this statement isn't quite true. However, you're not the only one who has made this sort of statement before, so don't feel too bad!

The amount of linear force that a wheel provides isn't completely related to the chain tension that is spinning the wheel, as John mentioned before, it's really related to the coefficient of friction (how sticky the wheel is) between the wheel and carpet.

If you take a step back and imagine that your front omni wheels are actually made of a material that really slips on the carpet, they won't be contributing the pushing force your robot can produce. As the chain pulls on the sprocket that turns the wheel, the traction heavy wheels in the back will be biting in to the carpet, while the front will basically be slipping. Basically, you take the coefficient of friction times the weight on each wheel to get how much force your robot can push with.

Hope this helps clarify!

Matt

Re: omni drive vs tank
 

That may be true but from experience I know that the omnis do help in a pushing match especially when helped by the back wheels.

Re: omni drive vs tank
 

All I got to say is TANK all the way man.