Posted by Daniel Garmendia at 1/10/2001 11:26 PM EST
Other on team #367 from Seaford High School.
My team is trying to decide how we want to steer our robot… The tank-like design would use two motors and we have a program for that. the go-cart like design would use three motors. Two motors for the forward/backward motion and the other one for changing the direction of the two powered wheels… Any advantages of this way over the tank way? There is a question of traction too… didn’t hear too well 'bout this… is the arena carpeted?
Posted by Justin Stiltner at 1/10/2001 11:55 PM EST
Student on team #388, Epsilon, from Grundy High School and NASA, American Electric Power, Town of Grundy.
In Reply to: tank or go-cart style steering?
Posted by Daniel Garmendia on 1/10/2001 11:26 PM EST:
: My team is trying to decide how we want to steer our robot… The tank-like design would use two motors and we have a program for that. the go-cart like design would use three motors. Two motors for the forward/backward motion and the other one for changing the direction of the two powered wheels… Any advantages of this way over the tank way? There is a question of traction too… didn’t hear too well 'bout this… is the arena carpeted?
Yes the arena is carpeted. If I were you I would go with the tank style. Its your choice but it is the easyist to design/build/drive/program and it has the ability to do a 0 radius turn which a car cannot do. and it would take a while for the car style to do a 180
also you wouldent need 3 motors since the speed controllers have a reverse in them.
its up to you but I would reccomend keeping everything simple and if you use a part design your robot to use the part like it is off the shelf that way you can just buy a replacement and not have to work on it to make it fit.
Justin Stiltner
Team #388
Epsilon
Grundy Va,
Posted by aTm at 1/11/2001 12:30 AM EST
Student on team #111, Wildstang, from Wheeling High School and Motorola.
In Reply to: tank or go-cart style steering?
Posted by Daniel Garmendia on 1/10/2001 11:26 PM EST:
I think that before you try to decide, you should first of all see which type of system would benefit your concept. If the robot is just going to go over the ramp, there’s no need for crab drive, as we call it. If you plan to be manuevering alongside the ramp, crab might be a great feature. If you were on my team, you would know that crab can make ANY robot better no matter what the circumstances, according to me of course. I loved driving crab, the manueverability, added difficulty, and complete control of any driving situation really played to my liking when Wildstang implemented the crab drive two years ago. Sure, tank drive would be easier, but your driver will be forever grateful, and so might you depending on your strategy, if you decide to go with crab. If you have the time, the motors, and the dedication, why not??
aTm
Posted by Michael Martus at 1/11/2001 6:57 PM EST
Coach on team #47, Chief Delphi, from Pontiac Central H.S. and Delphi Automotives Systems.
In Reply to: The Wonders of Crab ( Go-Kart steering)
Posted by aTm on 1/11/2001 12:30 AM EST:
Based upon your comments…
Any guess as to what type of drive Chief Delphi will have?
Posted by Lora Knepper at 1/11/2001 8:51 PM EST
Other on team #419, Rambots, from UMass Boston / Boston College High School and Seeking Sponsorship.
In Reply to: Re: The Wonders of Crab ( Go-Kart steering)
Posted by Michael Martus on 1/11/2001 6:57 PM EST:
: Based upon your comments…
: Any guess as to what type of drive Chief Delphi will have?
If the Chief doesn’t go crab, I will be forever shocked, and probably out cold on the pit floor ;o) Personally, I loved when 69 did crab last year…the few times I drove the base, I had a blast! (I was the arm operator :o) )
~ Lora
Posted by Anton Abaya at 1/13/2001 9:12 PM EST
Coach on team #419, Rambots, from UMass Boston / BC High and NASA, Mathsoft, Solidworks.
In Reply to: The Chief better go crab!!! It’s a tradition!
Posted by Lora Knepper on 1/11/2001 8:51 PM EST:
yah yah go lobstahs!
-anton
Posted by Joe Ross at 1/11/2001 3:26 AM EST
Engineer on team #330, Beach Bot 2001, from Hope Chapel Academy and NASA/JPL and J&F Machine.
In Reply to: tank or go-cart style steering?
Posted by Daniel Garmendia on 1/10/2001 11:26 PM EST:
There are several advantages to the tank style system. The most important is simplicity. Like you said, you already have a program that allows for tank style system, and mechanicaly the tank system is realitively simple also.
To go with a Crab system like chief delphi has so elegently demonstrated in the past is much harder. There are many more programming issues to deal with and mechanically it is more difficult as well.
tank systems can also give you more powered wheels on the ground, which gives you more pushing/pulling power if down properly. You do lose a little manuverabilty, but IMHO building a drive system that can get you from point A to point B reliably is much more important than being manuverable, especially since you don’t have any opponents this year.
: My team is trying to decide how we want to steer our robot… The tank-like design would use two motors and we have a program for that. the go-cart like design would use three motors. Two motors for the forward/backward motion and the other one for changing the direction of the two powered wheels… Any advantages of this way over the tank way? There is a question of traction too… didn’t hear too well 'bout this… is the arena carpeted?
Posted by Ken Leung at 1/11/2001 3:50 AM EST
Student on team #192, Gunn Robotics Team, from Henry M. Gunn Senior High School.
In Reply to: tank or go-cart style steering?
Posted by Daniel Garmendia on 1/10/2001 11:26 PM EST:
Well, it is really up to what your robot is designed to do. If you want a robust drive train to push goals around and go up the ramp, or push robot on stretchers to the end zone, you probably don’t need maneuverability, then the tank will suite you well. But, if you are planning to go pick up balls, either small or big, and try to chase after the goals to put balls in, then you want a lot of maneuverability so you are just floating around the field, doing whatever delicate turn or even sideway move you want, then tank drive is probably not your cup of tea. One thing I know about tank drive is that it is not hard to build a reliable one. So, the most important issue to figure out is you robot’s function. You may want the robot to do everything, but chance are, that will be too hard to accomplish. Pick what the robot is going to do, and build the device behind that robot.
Posted by Matt Berube at 1/11/2001 7:55 AM EST
Engineer on team #49, Delphi Knights, from Buena Vista High School and Delphi Automotive.
In Reply to: tank or go-cart style steering?
Posted by Daniel Garmendia on 1/10/2001 11:26 PM EST:
What everyone said below is right. A tank drive is both simple to construct and reliable. It is also fairly agile/manuverable. BUT, it is very inefficient. It runs straight just fine but it slows down ALOT as soon as you try to turn. I would strongly suggest to anyone wanting to build a tank drive that you consider powering each side with 2 motors.
Matt B.
T49
Posted by Dodd Stacy at 1/11/2001 11:22 AM EST
Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.
In Reply to: A warning about tank steer
Posted by Matt Berube on 1/11/2001 7:55 AM EST:
: What everyone said below is right. A tank drive is both simple to construct and reliable. It is also fairly agile/manuverable. BUT, it is very inefficient. It runs straight just fine but it slows down ALOT as soon as you try to turn. I would strongly suggest to anyone wanting to build a tank drive that you consider powering each side with 2 motors.
: Matt B.
: T49
A fairly simple and effective way to solve the inefficiency problem is to run 6 wheel tank drive, 3 wheels in line on each side, with the center wheels (under the machine cg) more heavily loaded than the other four. The side-skidding of the front and back wheels during turning then exerts very little drag because the wheels are very lightly loaded. The same effect can be had with track drive systems by putting a slight “rocker” or vee on the bottom of the track path. Good luck.
Dodd
Posted by CArobot at 1/16/2001 6:25 PM EST
Other on team #619, CArobot, from Charlottesville Albemarle.
In Reply to: Re: A warning about tank steer
Posted by Dodd Stacy on 1/11/2001 11:22 AM EST:
: : What everyone said below is right. A tank drive is both simple to construct and reliable. It is also fairly agile/manuverable. BUT, it is very inefficient. It runs straight just fine but it slows down ALOT as soon as you try to turn. I would strongly suggest to anyone wanting to build a tank drive that you consider powering each side with 2 motors.
: : Matt B.
: : T49
: A fairly simple and effective way to solve the inefficiency problem is to run 6 wheel tank drive, 3 wheels in line on each side, with the center wheels (under the machine cg) more heavily loaded than the other four. The side-skidding of the front and back wheels during turning then exerts very little drag because the wheels are very lightly loaded. The same effect can be had with track drive systems by putting a slight “rocker” or vee on the bottom of the track path. Good luck.
: Dodd
Why run 6 if only the middle two are going to carry enough weight to matter?
: Luke
Posted by Joe Johnson at 1/16/2001 9:33 PM EST
Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.
In Reply to: Re: A warning about tank steer
Posted by CArobot on 1/16/2001 6:25 PM EST:
Turning is a big reason to go with 6 wheel drive.
If you are trying to turn with 4WD or with a tank
drive, you are going to have to scrub your drive
mechanism across the floor.
If your front and back wheels are sharing the load
about equally, then you have a separation of about a
robot length between the scrub forces on the front and
back wheels. This puts a torque on your machine that
the drive system has to overcome. I have build a
number of robots that can barely turn at all without a
lot of heat being generated by the motors.
By going with 6WD, you effectly half the seperation
between the scrubbing forces. More than this, if you
look at the velocity vectors, you will see that in the
case of a square robot turning about its center with it
weight in the middle of the robot, the tires have to
move at a 45 degree angle to the direction of rolling.
Under the same situation for a 6WD robot with the
center wheels lowered so that they take more of the
load, there is almost no loss due to scubbing of the
wheels because the wheels that scrub are not loaded to
any significant amount.
Finally, considering the worst case of the CG half way
between two sets of wheels and a machine trying to spin
about its CG. Again, look at the velocity vectors.
Because distance between the drive wheels in the
fore/aft direction is about half the distance between
the wheels in the side to side direction, the velocity
vectors make a much smaller angle with the direction of
rolling of the wheels. This means less scrubbing.
BOTTOM LINE:
This is a great year to consider 6 wheel drive with the
middle wheels lowered a bit so the machine rock just
about a 1/4 inch.
Try it, you’ll like it.
Joe J.
Posted by Mark Garver at 1/16/2001 10:26 PM EST
Student on team #68, Truck Town Terror, from Waterford Kettering/OSMTech Academy and General Motors Truck Group.
In Reply to: 6WD – Highly recommended…
Posted by Joe Johnson on 1/16/2001 9:33 PM EST:
Hey Joe, the way this idea of yours sounds seems like you have tried this idea like in the pass couple of day?
Posted by Joe Ross at 1/17/2001 3:54 AM EST
Engineer on team #330, Beach Bot 2001, from Hope Chapel Academy and NASA/JPL and J&F Machine.
In Reply to: 6WD – Highly recommended…
Posted by Joe Johnson on 1/16/2001 9:33 PM EST:
Our rookie year (Toroid Terror) we used a rocking concept, but with only 2 wheel drive. We ran two wheels at the center of the robot and then in the center of the front and back, we used small fiberglass skids (and inch or two in radius). The skids were raised slightly off the floor so that the robot rocked (like Dr. Joe’s 6 wheel drive). We only weighed 70 lbs, but we were easily one of the fastest and most manuverable robots out there.
We discovered the major flaw with this system the next year. That year we tried virtually the same drive system, but the robot weighed 130 lbs. In this case, there was too much weight on the skids and the robot barely moved.
Dr. Joe’s 6-wheel drive solves the problem above by having more driven wheels on the ground. I would definetly consider trying it if I were you. It gives you a strong, manuverable robot, and you can easily be fast if you want to also.
Joe Ross
Beach Bot, Team 330
Posted by Bill Beatty at 1/17/2001 10:34 AM EST
Other on team #71, Team Hammond, from Team Hammond.
In Reply to: 6WD – Highly recommended…
Posted by Joe Johnson on 1/16/2001 9:33 PM EST:
I can’t wait to see it.
Posted by Anton Abaya at 1/20/2001 12:18 AM EST
Coach on team #419, Rambots, from UMass Boston / BC High and NONE AT THE MOMENT! :(.
In Reply to: 6WD – Highly recommended…
Posted by Joe Johnson on 1/16/2001 9:33 PM EST:
hmmm…
can we borrow joe for like a day or two?
-anton
Posted by Joe Ross at 1/20/2001 1:59 AM EST
Engineer on team #330, Beach Bot, from Hope Chapel Academy and NASA/JPL , J&F Machine, and Raytheon.
In Reply to: interesting…
Posted by Anton Abaya on 1/20/2001 12:18 AM EST:
: hmmm…
: can we borrow joe for like a day or two?
: -anton
Sure you can borrow me. What’s a ticket to boston nowadays?
Oh, you mean that Joe 
Joe Ross
Beach Bot, Team 330
Posted by Chris Hibner at 1/17/2001 8:04 AM EST
Coach on team #308, Walled Lake Monster, from Walled Lake Schools and TRW Automotive Electronics.
In Reply to: Re: A warning about tank steer
Posted by CArobot on 1/16/2001 6:25 PM EST:
We are a team that uses 4WD and swears by it since it is powerfual and the robot is extremely easy to drive if done properly.
As Joe mentioned below, in a 4WD drive system, the wheels must scrub sideways as the robot turns. If you sum the moments about the robot as it turns, you will see that you need one of two things in order to turn effectively:
- Your track must be larger than your wheelbase (considerably larger to be effective).
or
- Your coefficient of friction between your wheels and the ground must be greater in the fore/aft axis than in the side-to-side axis. This is why we make custom wheels for our robot. We use metal or plastic and keep the edges of the wheel teeth “sharp” while we round the sides of the wheels. Then, voila! - you get a significant difference in the coefficient of friction from fore/aft to side-to-side. Of course, this only works if you are on carpet (or another surface that will deform under a wheel) and your wheel teeth are a good thickness. The wheels are esentially like skis - sharp in one direction and rounded and slippery in the other direction.
The residual friction in the 4WD system makes the robot extremely easy to drive since when you release the controls, the robot stops turning very quickly. Thus, the drivers don’t really need to worry about compensating for overshoot in the turns.
I hope this helps anyone considering a 4WD tank steer system.
-Chris