3 wheel vs 4 wheel vs 6 wheel

[locohammerhead]

I NEED MAJOR HELP ASAP! My team has their minds set on a three wheel desighn and i keep telling them that its not stable and they wont listen and i need as much info about why those are not stable and why a 6 wheel or 4 wheel drive is the way to go. If you could contaCT ME ASAP! That would be great! my email is locohammerhead@hotmail.com just enter that for msn instant messenger aol is locohammerhead and yahoo is locohammerhead i will only be on the messengers for one more hour so if you could contact me that would be great! And if im not on please! email me here it is again locohammerhead@hotmail.com.

thank you,
Brandon Cook team 1256

[Rob]

Depending on your strategy, 3 wheel drive may be appropriate. The obvious problems with this concept are stability issues and less powered wheels on the ground. Advantages are higher manuverability and a lighter drivetrain than say a 6 wheel design.

In 1998 my team used a 3 wheel design, 2 powered wheels in the front and a caster in the middle back. In order to maintain stability we had .5" of ground clearance. In addition, we put small delrin skids on the bottom of the back corners in case they contacted the ground. As far as less powered wheels goes...We wanted to be quick and manuverable for that competition. While we had virtually no pushing power, we could escape from defensive machines using our manuverability.

My point is the following:
You should identify what qualities you want your drivetrain to have, and pick your design around them. List the advantages and disadvantages of each design. See if the advantages fir what you want, and see if you can come up with effective solutions for the disadvantages.

Remeber that people on your team will have vastly different ideas about what to do. Look to past robots from other teams for some inspiration on your ideas. Finally, compromise is sometimes the worst solution, you may have to give up on your idea, or convince others to commit to yours. It helps if you have some math or experiment results to back up the claims you make about your design ideas.

Good Luck,

Rob

[dhitchco]

Brandon,
as others have suggested, the optimal drive design is a big "it depends".

There are many examples of real-world 3-wheel (or overhanging) designs such as engine lift cranes for automobile repair, or drum lifter cranes for 55 gallon barrels.

More importantly, it is vital that you and the team come to some concensus on your design and then put your best foot forward. By far, the biggest problem will be if you do NOT stick to some pre-determined strategy. You know that !#@$% will happen, but at least you can stay that you chose a design wisely and then executed flawlessly....win or lose.

[locohammerhead]

well the team im on wants a arm that can turn 360 digrees and the 3 wheel desighn that they have in mind is really narrow and thats a big prob.

[Parker]

Originally Posted by locohammerhead

I NEED MAJOR HELP ASAP! My team has their minds set on a three wheel desighn and i keep telling them that its not stable and they wont listen and i need as much info about why those are not stable and why a 6 wheel or 4 wheel drive is the way to go. If you could contaCT ME ASAP! That would be great! my email is locohammerhead@hotmail.com just enter that for msn instant messenger aol is locohammerhead and yahoo is locohammerhead i will only be on the messengers for one more hour so if you could contact me that would be great! And if im not on please! email me here it is again locohammerhead@hotmail.com.

thank you,
Brandon Cook team 1256

What ever you do, don't use a pivot wheel!!!!!!!!!!!!!

My team used a pivot wheel last year and had major problems with steering. Our robot was incapable of backing up in a straight line. This screwed up our autonomous program.

If you do go with a three wheel design you should use a circular delrin skid.

As far as the number of wheels is concerned, that depends on your design. Personally, I'd use a four wheel drive robot because you get more power and it makes your drive train a lot more efficient.

[greencactus3]

3 wheel robot? or 3wd? slight difference. 2wd but with caster may be called a 3 wheel robot. a kiwi drive/killough platform 3wd robot would be really sweeet. a couple teams have already succeeded with those designs. and unstable.. well not necessarily. as loing as you have a nice big triangle it shouldnt be too unstable in itsself. just maybe a high cg will be bad. but that applies to all robots. and yes, as someone said. dont use swivel casters. omniwheels. skids, ball transfers, are a couple better options. but make sure if you use anything of the sort make sure they can support the weight. we destroyed a couple of our 'wheeliebarish' casters.

[i_am_Doug]

what bout tread?

[Koko Ed]

Originally Posted by locohammerhead

I NEED MAJOR HELP ASAP! My team has their minds set on a three wheel desighn and i keep telling them that its not stable and they wont listen and i need as much info about why those are not stable and why a 6 wheel or 4 wheel drive is the way to go. If you could contaCT ME ASAP! That would be great! my email is locohammerhead@hotmail.com just enter that for msn instant messenger aol is locohammerhead and yahoo is locohammerhead i will only be on the messengers for one more hour so if you could contact me that would be great! And if im not on please! email me here it is again locohammerhead@hotmail.com.

thank you,
Brandon Cook team 1256

I'm not sure how much a bunch of random outsiders on some messageboard is going to sway the arguement in your favor. I think you guys need to test out the theories yourselves and find out what works and what doesn't.

[SpaceOsc]

id argue that a 360 arm will cause your weight to shift to the gaps in between your triangle of wheels and may tip u over, if u are going with 3 wheels it better be low to the ground cuz when u hit one of those pvc pipes from the base of the goal tetra u might fall over, if u got a arm that spins 360 degrees (Turret Arm) then you can argue u dont neeed as much agility in your drive base, u just need to go backwards forwards and the ability to turn and most importantly not to fall over!!!!!!

of course there is some details that need clarifying, such as:

wuts the third wheel for? does it serve like a crab drive module? is it a castor? is it omni? is it even powered? and wut kind of config is it in? is the third wheel the leading wheel?


with arms that complex u really neeed a strudy box under your turret, also with a 6 wheel drive and or a 4wd you can have a larger base frame as im assuming most 3 wheel drive frames are smaller by default. and u do need room for that arm

ive been in situations like this before witha soburn team and usually can laugh about it on your own later when things go wrong, but if your teams not giving in then at least see wut the issues are and come up with ways to fix them now, like making the robot low, like using skids, and the such


-Osc-

[663.keith]

I can see a 3 wheel design for this years competition to be very unstable. It seems that we will see a lot of robots getting tipped over this year while trasfering tetras, or by another robot pushing them. A robot will have a very high center of gravity when it is holding on to a tetra, I would sugest trying to get the most contact with the floor as possible

[The Cyborg]

Our robot last year had a three wheel drive system, and there were a few ups and downs from having it:
First of all, we were tippy, and we also had a hard time programming the third wheel, since none of us last year knew C that well.
But, on the other hand, the third wheel made driving the robot significantly easier, since we specially programmed (after we learned to use C a little better ) only one joystick to drive the robot, and to have the wheel turn while we go forward at the same time, putting less stress on the wheels than a common four wheel drive.
A three wheel drive is good, and it is bad, it depends on what you have on the robot (and the experience you have, dont forget about the experience).

[Steve P]

Good luck moving in a straight line with a 3 wheel design.

[Gary C]

Originally Posted by locohammerhead

well the team im on wants a arm that can turn 360 digrees and the 3 wheel desighn that they have in mind is really narrow and thats a big prob.

Why not go ahead and build a circle for that matter.

[Jeffel]

treads are slow and they suck for quick turning and overall they suck and casters are horrible too. Its better to just use 4wd!

[663.keith]

Originally Posted by Jeffel

treads are slow and they suck for quick turning and overall they suck and casters are horrible too. Its better to just use 4wd!

treads can be very fast and easy to turn if done correctly. We have a robot that is by far the fastest we have built and he uses treads. conversely, one of our 4wd robots was terrible at speed, and could barely turn (it used a wonderful "Bounce turn"). I believe that treads work better than 4 wheels in many cases.