View Full Version : Why don't I ever see robots that steer like a car
Capt. Quirk
14-01-2008, 23:21
Wouldn't that be an advantage in this competition?
Wouldn't that be an advantage in this competition?
Teams have toyed with the concept before. 812 (2003) and 1135 have tried. It didn't work too well in one of those cases.
It's definitely been done in the past, but it would probably be under 1% of all robots in the last 8 or so years. I know my team did it in 2003 and had some success.
Kevin Sevcik
14-01-2008, 23:34
Ackermen steering is a definite advantage for smooth turns and probably has speed advantages. It's also nicer on the wheels and carpet. However, it's not terribly useful for precise positioning. Imagine if there was a trackball right beside your car. If you wanted to grab it, you'd have to pull a reasonably complicated two-point turn. Or pull all the way around, etc. A tank drive robot merely has to turn 90 degrees in place.
MrForbes
14-01-2008, 23:39
This is a discussion we've been having for a week now! no resolution in sight, either.
We're working on a car steering type chassis design, as well as playing with the control algorithm for last year's 6wd. It'll be interesting to see how this showdown comes out, we are sort of planning to build the Ackermann design and drive both around and see how they compare.
For those who had trouble with car type robots in the past, what specifically were the problems? Your help would be appreciated!
(and Kevin, it might even be better to make another quick lap and make another attempt at the ball!)
Capt. Quirk
14-01-2008, 23:47
This is a discussion we've been having for a week now! no resolution in sight, either.
squirrel,
Will your team be competing in Las Vegas Too?
MrForbes
14-01-2008, 23:50
We signed up for Phoenix and Los Angeles FRC regionals....no Vegas...although the FTC team wants to go to the Vegas FTC regional. We haven't figured out yet if they are, school might interfere with their fun.
The only plus i see to having the front wheels spin like a car is you keep your motors running at top speed while you turn you never slow down as you turn.
As with a tank steer you have to cut power to half of your drive train in order to turn so potentially you are losing speed. Not much but you are....
MrForbes
15-01-2008, 00:05
Yup, and if you design the robot with the CG about 6" off the floor like we are, you should be able to just zip around corners like nobody's business.
Yup, and if you design the robot with the CG about 6" off the floor like we are, you should be able to just zip around corners like nobody's business.
Very true if you gear it right nobody will be able to catch you as well
1075 did a very "out there" drive as far as FIRST goes in 2003, our rookie year.
Anyone that was at the Canadian Regional that year (now Greater Toronto Regional, as there are now TWO Canadian Regionals!) would have seen it. I think Delphi E.L.I.T.E (FRC#48) gave us an award for most unique drivetrain.
It functioned a bit like a tricycle, we had two undriven wheels at the back of the robot, and an 8" wide track driven by the two CIMs and two Bosch drill motors they used to give us. Then we swung the whole track unit about a point at the front of it. We used a potentiometer on the pivot to track its location, and our autonomous mode was able to climb the ramp very quickly.
I remember that we had a match against one team whose autonomous mode never left the starting box, but instead extended an arm up and over the plexiglass border to reach the pyramid of boxes. Our drivetrain allowing us to turn at full speed got our whole robot to the boxes before they could get their arm there.
This particular unit was plagued by a problem with our inexperience at building drivetrains. It used a miter gear, but we didnt support it closely enough, and under load they were skipping teeth and shredding the gear. We finished 2nd in the competition, mainly because the gear was so shredded we couldn't even climb the ramp.
Capt. Quirk
15-01-2008, 01:12
We signed up for Phoenix and Los Angeles FRC regionals....no Vegas...although the FTC team wants to go to the Vegas FTC regional. We haven't figured out yet if they are, school might interfere with their fun.
I'll come and check out your bot in LA. We recieved our funding too late to be able to compete close to home. So were going to Vegas instead.
65_Xero_Huskie
15-01-2008, 08:56
Wouldn't that be an advantage in this competition?
What do you mean drive like a car?
Like Frontwheel Drive/Backwheel steering?
Vice versa?
I dont get it. I know many robots have done that.
GaryVoshol
15-01-2008, 08:59
Perhaps the reason is that teams that have the capability of designing a car-like steering mechanism also have the ability to go to an even more agile design - swerve or crab drive.
Here are a few images of previous robots with steering mechanisms similar to what have been discussed in this thread:
http://www.firstroboticscanada.org/site/node/410
http://www.firstroboticscanada.org/site/node/367
http://www.firstroboticscanada.org/site/node/325
http://www.firstroboticscanada.org/site/node/323
team1203 4life
15-01-2008, 09:29
Wouldn't that be an advantage in this competition?
because the turning radius is to large and would put you out of position
p.s sorry if this was already posted didnt read through all of them
Jherbie53
15-01-2008, 09:51
Like the others have said, it would be hard for you to turn around and go backwards in a quadrant. Other than that, this years game would promote it I think. If you decided not to hurdle the trackball or pick the trackball up off the ground, then you could build a really nice drive train that turns easy and could push the trackball around the track. I don't how easy it would be to build a CAR like drive train,( I'm not that technically inclined in this area ).
The reason why I think most teams don't use it is, like Kevin Sevcik said, you have to do a Y turn to turn around and its so much easier to have a drive train that can spin in a tight radius. Another reason is that it might be harder to build a CAR steering mechanism rather than lining up 6 wheels and running chain to all the wheels from a gearbox.
1086wulf
15-01-2008, 10:53
Car like steering was not really advantageous in the past because the games were more of maneuverability. This year however, since you will be running around the track, I would think if your strategy is to just run around to get points then it would work well. If you are herding it may cause some problems if you lose control and try to get the ball back.
Kit Gerhart
15-01-2008, 12:39
Wouldn't that be an advantage in this competition?
This year, for the first time since I've been involved with FIRST (12 years) we discussed car type steering briefly. For this game it might have an advantage in that you would have better precision when driving through holes in traffic than with tank type drives. The down side, as others have mentioned, is that you can't "turn in place" as with tank drive. Because of it's simplicity, I'm sure most teams will use tank drive this year, but will be practicing some different driving skills than for most previous FIRST games.
Team 1504 is making this kind of steering.
Isn't overdrive NASCAR for robots with a huge ball?
R3P0
My typical overthink analysis of this question:
Ignoring other aspects of the game, if you want to go just for the absolute minimum lap time, I suspect that an automotive-style drive train and ackerman steering system would be the ticket. In either rear-wheel drive or four-wheel drive form, in principle there should be less frictional losses and smoother direction change control.
One gotcha with this is your un-steered wheels need to compensate for the different driven path length around corners. A differential can lead to sitting still with one driven wheel spinning while drifting (sliding) a solid axle takes more finesse to drive and re-introduces frictional losses, so I'd opt for differential control of the motors driving the wheels (sync'ing them to the steering angle).
In the real world of Overdrive I think all this is moot, because it will be pretty darn hard to get a clear lap to make use of the little bit of extra speed you might have. Besides, us oldtimers recall a certain Evil Machine with six-wheel drive and tank steering that just plain flew around the field a few years back, proving that drive system can be fast, manuverable and push like an irresitable force - without any complicated steering system.
deshirider430
15-01-2008, 13:13
612 (05') http://www.chantillyrobotics.com/photo_gallery/main.php?g2_itemId=875
What I'd like to see is a tractor-style turning mechanism. 3 CIMs on 1 transmission that drives 2 rear wheels from a differential. To turn, all you do is brake the side you want to turn to. Put unpowered omnis on the front and BAM there you go -- seems easy enough right?
Capt. Quirk
15-01-2008, 23:59
One gotcha with this is your un-steered wheels need to compensate for the different driven path length around corners. A differential can lead to sitting still with one driven wheel spinning while drifting (sliding) a solid axle takes more finesse to drive and re-introduces frictional losses, so I'd opt for differential control of the motors driving the wheels (sync'ing them to the steering angle).
The easy way around that is to just let your inside wheels freewheel through the corners. The differential and "Steering Brakes" like JesseK suggested would turn wickedly fast. Programming for the turn angle or using a Go-Kart style chassis that lifts 1 wheel and with programming, could drive 3 wheels would be another option.
Nice pictures deshirider430, how did it work?. I was worried that using the window motors would limit how quickly the bot could change directions?
What I'd like to see is a tractor-style turning mechanism. 3 CIMs on 1 transmission that drives 2 rear wheels from a differential. To turn, all you do is brake the side you want to turn to. Put unpowered omnis on the front and BAM there you go -- seems easy enough right?
A differential wouldn't be hard to make and I think multiple motors feeding a differential would be a great idea, Especially for the 6 wheel drive "tractor style" drive train. All it would take is steering brakes and then the outside bank would receive full power.
My typical overthink analysis of this question:
Ignoring other aspects of the game, if you want to go just for the absolute minimum lap time, I suspect that an automotive-style drive train and ackerman steering system would be the ticket. In either rear-wheel drive or four-wheel drive form, in principle there should be less frictional losses and smoother direction change control.
After going through a similar overthink analysis, we came up with a different approach that should beat an automotive-style drive train with Ackerman steering - and arguably almost any other "standard" system. I won't just give it away, but let's just say that it involves reducing the deceleration time required to make the turn at the end of the Lane Divider to the absolute minimum amount of time possible, and constructing the ability to withstand repeated 53-G impacts into the robot. :)
-dave
.
After going through a similar overthink analysis, we came up with a different approach that should beat an automotive-style drive train with Ackerman steering - and arguably almost any other "standard" system. I won't just give it away, but let's just say that it involves reducing the deceleration time required to make the turn at the end of the Lane Divider to the absolute minimum amount of time possible, and constructing the ability to withstand repeated 53-G impacts into the robot. :)
-dave
.
So you decided to go with this, afterall?
So you decided to go with this, afterall?
We will see after the CDR on Saturday. Either way, it is a fun idea (if we don't go with it, it may still be a fun off-season project to prepare for IRI).
-dave
Travis Hoffman
16-01-2008, 02:22
Because of it's simplicity, I'm sure most teams will use tank drive this year, but will be practicing some different driving skills than for most previous FIRST games.
Actually, those who were adept at patrolling the area around the rack by driving in arcs last season may discover that that skill directly translates into making smooth gradual turns through the lane dividers with a tank steering setup this season.
Travis Hoffman
16-01-2008, 02:26
After going through a similar overthink analysis, we came up with a different approach that should beat an automotive-style drive train with Ackerman steering - and arguably almost any other "standard" system. I won't just give it away, but let's just say that it involves reducing the deceleration time required to make the turn at the end of the Lane Divider to the absolute minimum amount of time possible, and constructing the ability to withstand repeated 53-G impacts into the robot. :)
-dave
.
Bat-Steer (http://community.discovery.com/eve/forums/a/tpc/f/9401967776/m/4301969919/p/1)? Holy CO2 grapnels (http://books.google.com/books?id=ij-xvNBcwJUC&pg=PA38&lpg=PA38&dq=batmobile+grapnels&source=web&ots=74TCDtS9hc&sig=QE19UKnaqnn4DrxZvlRRCSkeqBU), Batman! :p
Capt. Quirk
16-01-2008, 02:55
and constructing the ability to withstand repeated 53-G impacts into the robot. :)
-dave.
By the ball, wall or other robots? :ahh:
Bat-Steer (http://community.discovery.com/eve/forums/a/tpc/f/9401967776/m/4301969919/p/1)? Holy CO2 grapnels (http://books.google.com/books?id=ij-xvNBcwJUC&pg=PA38&lpg=PA38&dq=batmobile+grapnels&source=web&ots=74TCDtS9hc&sig=QE19UKnaqnn4DrxZvlRRCSkeqBU), Batman! :p
Invert the solution. :)
Vikesrock
16-01-2008, 03:51
Invert the solution. :)
Wait.....the field has secret CO2 grapnels built in to sling your robot around the corner?
MrForbes
16-01-2008, 09:54
Actually, those who were adept at patrolling the area around the rack by driving in arcs last season may discover that that skill directly translates into making smooth gradual turns through the lane dividers with a tank steering setup this season.
We're working on control changes to make this as easy as possible....which kind of does away with the need for a robot with car type steering. First tests on it yesterday were very successful.....6wd, driven with a (spring loaded to return to center) steering wheel and throttle.
Alan Anderson
16-01-2008, 11:16
...and constructing the ability to withstand repeated 53-G impacts into the robot. :)
I think you also need to assume the ability of the field to withstand the same impact, as well as the ability of the center alliance drivers to withstand the repeated assaults on their senses.
Capt. Quirk
16-01-2008, 11:34
First tests on it yesterday were very successful.....6wd, driven with a (spring loaded to return to center) steering wheel and throttle.
Are you talking about the operator interface?
MrForbes
16-01-2008, 11:40
yes, I am talking about the OI.
I think you also need to assume the ability of the field to withstand the same impact, as well as the ability of the center alliance drivers to withstand the repeated assaults on their senses.
Our testing program involves the use of a field mock-up and one of these...
http://ecx.images-amazon.com/images/I/31TBV2WYKNL._AA280_.jpg :)
-dave
.
Travis Hoffman
16-01-2008, 12:04
Invert the solution. :)
*sings in aggravating childish whining tone* I know what it isssss-sssssss.......
So if Batman is not the appropriate movie, would it be more like Austin Powers on the cushman or Herbie fully Loaded?
whytheheckme
04-02-2008, 12:13
http://www.chiefdelphi.com/forums/showthread.php?threadid=63217
:D
FIRSTMa2104
11-02-2008, 12:52
Our team is working on a steering method that simulates the driving of a car in a racing game. Rather than going with a load of complicated sensors, we're planning on coding everything in algorithms that we can change easily whenever we need to. We're planning on having incremental steering for the front wheels and a differential gear system for the rear wheels.
Team 135
11-02-2008, 15:22
We thought about it and thought that it should be good for this competition. The main reason that we did not do it was because it was complicated. Not that we could not have built it and gotten it to work but there are a lot of places that failure could happen. Our goal for this year from pre 6 weeks was to keep it simple stupid.
MrForbes
11-02-2008, 15:32
We built a prototype Ackermann steering robot using the kitbot chassis, it was quick and easy to build and worked ok, but the steering radius was pretty large and we also figured out how to make a 6wd skid steer more controllable...so we gave up on the car steering idea.
FIRSTMa2104
11-02-2008, 16:18
We saw the same problem but we fixed it by changing the size of the wheels.
Kendal Reed
11-02-2008, 16:51
We're doing it. (http://www.chiefdelphi.com/forums/showthread.php?t=63122) Our drive team may regret it once they see this thread, but... we're doing it now. :rolleyes:
(Ours will be rear wheel drive only, with each rear wheel connected to a pair of CIMs via one gearbox and the differential functionality handled entirely in software.)
robostangs548
11-02-2008, 20:47
I really think that it would, that is why we just might be doing it :P
http://robostangs.tonch.com/hollaatchaboi.jpg
We figured out how to do a system that is four wheel drive and four wheel steer with a diff in the middle and rack and pinion steering
mattotters
11-02-2008, 21:40
I really think that it would, that is why we just might be doing it :P
http://robostangs.tonch.com/hollaatchaboi.jpg
is that pot i smell? and thats pretty sweet really sweet
robostangs548
11-02-2008, 21:59
is that pot i smell? and thats pretty sweet really sweet
Why thanks, we will have a vid up in the next 2 hours or so...
robostangs548
11-02-2008, 23:52
Video is up!
http://robostangs.tonch.com/asdf.html
Ackerman drives can theoretically keep the front wheels locked straight and have a tank steer mode to turn in place if you needed a smaller turning radius.
Back in 2001 competition my School Team (616) had Rack and pinion steering. It worked well (though we bought a trillion limit switches).
As a few other's have posted, the turning radius is what kills you. If you're off track at all (read: pulling into a parking space all jacked up), you almost always have to backup and try again. Building and programming the system was awesome though (back when we programmed in P-Basic.)
Perhaps when the fields get a little larger, and traveling around the (larger) field has more importance in the game, rack and pinion steering will come to the forefront. Right now though, manuverability is what's important.
Matt
robostangs548
12-02-2008, 12:22
Back in 2001 competition my School Team (616) had Rack and pinion steering. It worked well (though we bought a trillion limit switches).
As a few other's have posted, the turning radius is what kills you. If you're off track at all (read: pulling into a parking space all jacked up), you almost always have to backup and try again. Building and programming the system was awesome though (back when we programmed in P-Basic.)
Perhaps when the fields get a little larger, and traveling around the (larger) field has more importance in the game, rack and pinion steering will come to the forefront. Right now though, manuverability is what's important.
Matt
That is why with a quadrasteer design, you can crab walk a 45 degree :)
FIRSTMa2104
12-02-2008, 17:37
I really think that it would, that is why we just might be doing it :P
http://robostangs.tonch.com/hollaatchaboi.jpg
Funny, we are using the same motor to steer.
Ed Sparks
24-02-2008, 01:26
Team 34 has an Ackerman steering system this year with a limited slip differential.
Here's the front end (without bumpers) ......
http://www.firstcadlibrary.com/pics/Robot2008-14.jpg
Top view of the front end .......
http://www.firstcadlibrary.com/pics/Robot2008-13.jpg
Here's an overall view of the rear end .....
http://www.firstcadlibrary.com/pics/Robot2008-10.jpg
A close up of the drive train ......
http://www.firstcadlibrary.com/pics/Robot2008-11.jpg
A close up of the diff .......
http://www.firstcadlibrary.com/pics/Robot2008-15.jpg
I took these pictures before we attached our lift. We'll be at the Peachtree & Bayou regionals. See ya' soon.
Blue_Mist
24-02-2008, 01:34
Interesting tread. Spray paint? If so, I anticipate blue streaks all across the carpet...
Interesting tread. Spray paint? If so, I anticipate blue streaks all across the carpet...Nah, blue nitrile I think it's called. It's a traction material that comes blue--no streaks on the carpet.
Ed Sparks
24-02-2008, 01:44
Interesting tread. Spray paint? If so, I anticipate blue streaks all across the carpet...
Nope. It's Nitrile roughtop rubber belting available from McMaster-Carr.
Team 34, that is a beautiful and impressive drivetrain. Out of curiosity, why did you choose to go with a differential rather than have one motor for each side and vary their speeds as you turn? It seems to me that if you lose traction on one wheel, you lose about half your power either way.
For video of an Ackerman-steering robot in action, look here:
http://www.chiefdelphi.com/forums/showthread.php?t=64389
Ed Sparks
24-02-2008, 17:19
Team 34, that is a beautiful and impressive drivetrain. Out of curiosity, why did you choose to go with a differential rather than have one motor for each side and vary their speeds as you turn? It seems to me that if you lose traction on one wheel, you lose about half your power either way.
1. We don't believe there is a great need for 'brute force' this year. One two speed gearbox should do it. High speed for getting around the track in a hurry, and low speed for pushing our way out of a jam. We have plenty of speed and power in high to move out in a hurry and the CG is so low we can take a corner at full speed. The turn radius is about 3 feet.
2. Our system utilizes a clutch to provide torque transfer in the event of one wheel loosing traction. That metalic device just behind the blue diff is an adjustable clutch. We can adjust this clutch to whatever torque we want so we have in effect created a "Limited-Slip" differential system. In general, we set the torque high enough so we can still move in the event one wheel looses traction but not so high that the rear axle acts as a solid axle during cornering.
3. Weight. It weights less than a system that has independent gear boxes. We wanted to be sure that we had weight to use for our lift. As it turns out, the base you see pictured weighs only 42 lbs which gave us plenty of room for lift development. The whole robot only weights less than 100 lbs.
4. We wanted to use a CIM on our lift and I'm glad we did. It's ultra fast and smooth as silk.
5. Simple. It looks complex but this thing is actually easy to maintain. The software was easy, it avoids any issue with two gearboxes stuck in an undesireable condition, and it's layed out well.
Team 1504 is making this kind of steering.
Isn't overdrive NASCAR for robots with a huge ball?
R3P0
Here's our front forks for our steering
Fred Flintstone would be proud!
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