independant 4 wheel drive

[ufa_mike]

I noticed this year that the teams who did well didn't have a very fancy design or anything they had a robot that drove well and had good speed and torque. I thought about it and decided that the best way to maximize traction and driveabiliy is to have all four wheels spinning at the same rate. This means four seperate gearboxes and a shaft encoder on each wheel. Then a program that keeps thmspinning the same speed. I was wondering if anyone else has had any experience with a system like this and if it woked or didn't work ect.

[Ryan F.]

This year we used a simple system with the drill motors using the FIRST supplied gearbox, and made I made a grearbox for the CIM motors that had a relatively simular output speed. All we had to do in the end was chain the two ouput shafts together, and it made a simple and reliable system that satisfied basically all we needed/wanted it to do.

We place the CIM motors on the back wheels, and the Drill motors on the front wheels, thus making out 4 wheel drive.

Simple is good.

[Alex Cormier]

Originally Posted by ufa_mike

I noticed this year that the teams who did well didn't have a very fancy design or anything they had a robot that drove well and had good speed and torque. I thought about it and decided that the best way to maximize traction and driveabiliy is to have all four wheels spinning at the same rate. This means four seperate gearboxes and a shaft encoder on each wheel. Then a program that keeps thmspinning the same speed. I was wondering if anyone else has had any experience with a system like this and if it woked or didn't work ect.

how about just 4 wheel drive? have one or two motors for each side, run a chain of that spoket to the front whhels and on another sproket to another whell in the back.. ill look for photos... o i rememebr www.gosparx.org *2004 photos* look and you can see what i am tlaking about.

[ufa_mike]

The problem with the 2 wheels move together idea is that to have good tunability your front wheels have to have less traction than the back wheels and slide when u turn. This means that your traction limit is lessened in the 2 wheels move together idea. WHat I really menat was to have each wheel move independantly from eachother so each wheel is at it's traction limit. Anyone know what I'm talkin about.

Any help appreciated

[Ryan F.]

I think the problem may lie in the pneumatic tires. We have a very simular 4wd drive system on out last years robot, and when we tested those tires on it, it jumped, and had horrible turning ability. I'm not sure exactly what we have...but we put some 9 inch wheels on, and that solved the problem.

[Biff]

Originally Posted by ufa_mike

The problem with the 2 wheels move together idea is that to have good tunability your front wheels have to have less traction than the back wheels and slide when u turn. This means that your traction limit is lessened in the 2 wheels move together idea. WHat I really menat was to have each wheel move independantly from eachother so each wheel is at it's traction limit. Anyone know what I'm talkin about
Any help appreciated

.Are you talking about "crab" or "swerve" drive? There are drawings and info under those headings. And some teams that have people posting here can answer as to the complexity of the mech and programing. Most that I've seen have modules that swivel, truned with one chain per side. When looking at a swerve drive at Grand Valley, the team (sorry I forget their number) liked it but said it was a little over geared and tended to eat Fisher Price motors. I made a suggestion to put a spring loaded Z in the chain, on the outside of each "turning chain" and a piston or something on the inside so they could get the modules to form a O and do a tank style turn with out having to have the masses unballanced or be really geared down. I hope someday to be able to work with Students that have the machining (sp) skills to attempt a crab or swerve, for now I planning to stick with 4 wheel dirve and over power it to be able to turn.

[The Lucas]

Originally Posted by ufa_mike

The problem with the 2 wheels move together idea is that to have good tunability your front wheels have to have less traction than the back wheels and slide when u turn. This means that your traction limit is lessened in the 2 wheels move together idea. WHat I really menat was to have each wheel move independantly from eachother so each wheel is at it's traction limit. Anyone know what I'm talkin about.

Any help appreciated

Are you trying to "peel out" (raise the speed) the front wheels to lower friction for turning? Or are you trying to keep the speed of the outer wheels constant (front will want to move faster since it has less load) during a turn to reduce slipping?

[Grommit]

I'll avoid addressing items already mentioned and repeated, and state the following out of our team's experience:

Driving pairs of wheels on each side with one output shaft with chains going to each wheel in the pair, and having identical gearboxes on each side, has been successful for us. Fortunately, our motors wore down at roughly the same rate and it kept both sides at the same speed.

On the other hand, this year our drivetrain was a living NIGHTMARE. We had four individual modules, with all the gears mounted inside the wheel, and motors sticking out of the wheel suspended in $125 bearings (cha-ching!). All four modules rotated by way of a window motor on a chain that ran on the top of the robot, creating a mess that made mounting difficult. But the worst part was that the wheels broke down every so often, making them very high-maintenance. And did I mention that they were supposed to run at the same speed, but in actuality were quite a terrible mess? I'm not sure if this is electrical or mechanical, but half the time one of the four wheels was running slower than the other four and messing the bot up. Also, it is hard to align the wheels, and if your wheels are as wide and high traction as ours, you're dreaming if you think we can tank. Thus, I strongly recommend you consider carefully if you want a swerve drive next year, and no matter what, talk to people who have done it before, such as Bill Gold and Jim Gold on Sea Dawgs #258, who definitely can give you a good idea of what to do and what not to do with a swerve drive.

[Madison]

Originally Posted by ufa_mike

I noticed this year that the teams who did well didn't have a very fancy design or anything they had a robot that drove well and had good speed and torque. I thought about it and decided that the best way to maximize traction and driveabiliy is to have all four wheels spinning at the same rate. This means four seperate gearboxes and a shaft encoder on each wheel. Then a program that keeps thmspinning the same speed. I was wondering if anyone else has had any experience with a system like this and if it woked or didn't work ect.

Wheels driven by chain or gears are spinning at the same rate.

[Alex Cormier]

found one laready.. go to picture galleries,2004,regionals,buckeye.. you can find many of my bot and see the chians good..

http://www.chiefdelphi.com/forums/pi...&quiet=Verbose

[RoteAugen]

Originally Posted by ufa_mike

I noticed this year that the teams who did well didn't have a very fancy design or anything they had a robot that drove well and had good speed and torque. I thought about it and decided that the best way to maximize traction and driveabiliy is to have all four wheels spinning at the same rate. This means four seperate gearboxes and a shaft encoder on each wheel. Then a program that keeps thmspinning the same speed. I was wondering if anyone else has had any experience with a system like this and if it woked or didn't work ect.

If you are going to atlanta, seek out team 138. We'll be happy to help provided we arent in a rush to get to a match

[JoshJ]

For simplicity, like its been said, you can just link each side with chain and sprockets or gears, etc

For driveability, i would use a gyro to give you steering feedback and have it adjust ur drives(not that i have any experience with them, but that seems to be the general trend around here)

For traction, maybe you could use a non powered wheel with an encoder on each driving side. That way, if a wheel slips, you can slow it down to the speed of the non powered wheel, (or just above it, depending) until the two speeds match, then you know that you are getting grip, and are good to go. Let me know what you think

-Josh

[sburro]

My team had a 4- wheel drive system that involved linking the front tires with the rear ones with chains. I did notice, though that when the robot went to turn, it "hopped" like a 4-wheel drive truck on a dry day. I myself was going to post a qeustion that asked if anyone had a somution without loosing to much traction?

[sanddrag]

Originally Posted by sburro

My team had a 4- wheel drive system that involved linking the front tires with the rear ones with chains. I did notice, though that when the robot went to turn, it "hopped" like a 4-wheel drive truck on a dry day. I myself was going to post a qeustion that asked if anyone had a somution without loosing to much traction?

This is not because of the chains linking. It is because the wheelbase is longer than the track width is wide and there is too much traction.

[MikeDubreuil]

We've developed an excellent solution for this. I'm fairly sure it's not an original idea, however I don't know who to credit it too.

Our drive train consists of 4 drive modules. Two are powered by the Chips, and two are powered by the drills. The motors are mounted horizontally, making their polarity/wheel direction the same. Worm gears are used to transfer the power horizontally to vertically (to the wheel). With a little programming and gearing the motors spin at about the same RPM.

Even with using the sticky pneumatic tires we've never blown a fuse. We also rarely lost a pushing match. Our only problem is that we had turning problems, IE: hopping. I think we're going to solve that via some omni-wheels. With some tweaks in the off-season, we are going to make this our standard drive train.