# Making your robot drive easier

I have noticed that all teams who consistently win don’t have a complicated design but seem to drive well. SO I sugested to the team we just make a robot that drives and drives well, this year. But I’m not quite sure whet else to do to make it drive easier. Other than making a really solid gearbox with no slop. And ramping the controls.

any ideas?

less c.o.f. wheels so with that spiffy nice gear box in high gear you could turn very easily… or make omni wheels! Yay! omni wheels

Intuitive controls. Even if you have a complex drive system, if you have a simple/intuitive control system your drivers will be able to drive it.
And practice, lots of practice.

Here’s an example (idea taken from some bots, controls from an arcade game):
A bot has four wheels. each has its own drive motor. Each can also spin a continuous 360 degrees (Can spin forever without reversing). Complex drive.
On the control side: 2 joysticks. One for the left, one for the right. Each side goes the direction the joystick is pointed. Up means forward, down means backwards, left means left, right means right. U.L. means 45 degrees to the left from forward. The farther from center, the faster it goes. Front/back wheels are linked in code.

This control system is simple, and follows a standard skid-steer setup (with some mods). however, you can translate (go left/right w/o rotating) by pointing the the joysticks that way. So basically, you can make your robot dance, or rotate while moving forward (advanced technique).

Granted, this sort of set-up would take lot’s of practice. lots and lots.

I’m going to disagree with PitBull a little bit…

I think the key to an easy-to-drive drivetrain is having the optimal lateral coefficient of friction (not the lowest). That is much easier said than done, but here is why I feel this way:

1. If you have too much lateral friction, your drivetrain will not turn well (or maybe not turn at all). This is obviously not desirable for many reasons that everyone knows, so I’m not going to explain further.

2. If you have too little lateral friction, the robot can become difficult to drive. Why? Inertia!

When your driver let’s go of the stick, the robot will continue to turn. The amount of excess turn is inversely proporional to the amount of lateral friction you have. If you have too little friction, the robot becomes hard to control since the driver will let go of the stick where he/she want the robot to stop turning, and the robot will overshoot past the stopping point. This can be overcome with a lot of practice, but the whole point of this thread is to make a robot that doesn’t require as much practice to drive.

Over the years, we have had robots that had very little lateral friction and I will definitely say that they were our most difficult robots to drive. Once we went to 4-wheel drive, the robots would stop turning the instant the driver let go of the stick - these robots were very easy to drive.

So, the moral of the story is: less friction is not always better. There is an optimal amount of friction - good luck achieving it.

Make a really solid gearbox. I find that you don’t need any more then 2 speeds. High and Low. Also you can have wheels with a high C.O.F but to make your bot turn easier you need to 6 wheel drive and lower the middle set of wheels about 5 thou lower then the other ones and there you have a killer drive system.

SNIP

to make your bot turn easier you need to 6 wheel drive and lower the middle set of wheels about 5 thou lower then the other ones and there you have a killer drive system.

I would really like to hear more about this idea. Anybody make a six wheeled robot with all wheel drive??? I saw team 418 at the Lone Star Regional but didn’t get an up close look at their drive. I was more impressed with their ball catcher and laminated wood biggens ball arms :ahh:

post some pics or PM me or send a link to your site with photos

Thanks,

next year.

APS

[email protected]

Team 233 has a 6-wheel all drive system. I’m assuming, when you say 6-wheel all drive, you simply mean all wheels are drive wheels.

Anyway, each side is linked to a joystick for tank driving. The middle wheels are lowered just a bit to give us the ability to turn well, and the friction of six wheels sitting on the ground makes us very hard to push sideways. I don’t think our team will ever change from this 6-wheel setup (unless we get a radically different game from FIRST).

Here’s a link to the 47 robot who uses a sweet 6 wheel drive with chain drive on each side team 47’s bot

and here is the 254/60 “bionic poof” with their 6 wheel drive with the middle ones lowered a little bit

i think, correct me if i am wrong, that 25 was one of the teams that most successfully implemented this last year and many teams have used similar ideas.

We had a 6-wheeled robot this year…I don’t know whether it was six-wheel drive though. It took us a few days to get the middle-axle lowering set the right way, but it helped a LOT. Oh I should tell you that we used some spiffy donated tracks, and it made us look like an R/C tank out there.

Robo pics and videos are here: http://www.sau53.org/net9/First/media.htm
You may also see the team at PARC in May. I wish I could go, but I’m going to Washington D.C. that weekend :-C

i posted a pic of our 6 wheel drive train. theres some stuff in the way, but you can still see most of it.

http://www.chiefdelphi.com/forums/pictures.php?action=single&picid=7644

Watch your speed. I saw some teams build robots that were incredibly fast, but I can just imagine the nightmare those drivers go through whenever they try to do something rather than getting from point A to B.

feedback - PID control loop on the steering

using the default code to let the position of the joysticks control how much voltage (pwm) is thrown at the drive motors is as crude a control method as you can get (well, there is one thats worse, only having a GO/STOP switch :^)

no matter what your drivetrain is if you put yaw rate and/or linear speed sensors on the bot, and use feedback, you can remove all the nonlinearitiy, inertia, friction… from the control system and MAKE the bot do exactly what the driver is commanding at any given instant.

another idea is to add a ‘jog’ function to your control system - I posted stuff about this before - let me search and see if I can find it…

yep,heres the thread - BTW it contains several other simple ideas on how to make your bot better:

Let me elaborate a little. We used the brecoflex tracks this season. They have and awesome amount of friction (cof ?). The problem we had was we could turn because they spread out on the floor 26" and was only 21" wide. To solve the we put a larger we wheel in the center reducing the amount of track on the ground by about 45% in either direction. This gave us just the right amount of track on the ground to turn and allowed us to move alittle faster.

If you have any questions about it PM me or IM me.

-Pat

if you are really looking for a good team’s drive that uses 6 wheels, check out team 42. for the past 4 years they have gone with the same drive, and its really worked out well for them.

Best way to drive well… have a great driver! A great driver can overcome and drive system.

we did six wheel direct drive, with lowered center wheel.

here it is without any end-efffects:

http://www.chiefdelphi.com/forums/pictures.php?s=&action=single&picid=6516&direction=DESC&sort=date&perrow=4&trows=3&quiet=Verbose

Roger, where those red plates powdercoated? or just painted? where did you get those wheels btw?

plates are powdercoated, and the wheels are 2" x 8.5" skyway bead-lok modified using a dremel and a belt sander.

You could aso check out team 25. They have had a great 6 wheel drive system for the last two years.

Well, while we’re on the subject of Home Depot cart type drive systems (you know, 6 wheels with center ones lower), 980 and 599 had them too.