4wd or 2wd need help

[itay_ms]

hi we are a rookie team and we need some advice what is better 4 motors with 6 wheels or 2 motors with 4
i hope you will help me

[BillP]

What you really need to consider is what you want your robot to do. If you want a strong robot that can push other robots around, I would recommend 6 wheels and as many motors as you can put together. However, if you want a quick, agile robot that will run circles around the "bully-bots", go with 4 wheels and two motors. In either case, you should look into the possibility of (at least) a two speed gear box so you can get the benefits of both strength and speed.

Good luck!

[DjAlamose]

Well, 6 wheels is much better than 4 wheels if you plan on getting up ramps (these would be on other robots). 6 wheels also will give you more traction on the playing field. Having 4 wheels makes things easy to design and build. So there are trade offs between the two.

As for motors, you don't need 4 motors with 6 wheels, 2 would be just fine. When selecting the number of motors you are looking to see how much power you want. The more motors, the more power, the more complexity.

So 6 wheels is more complex than 4, but has better qualities. And 4 motors has more power and more complexity. It all depends on what you and your team feel comfortable with designing and building.

Personally though, I would go 6 wheels and 4 motors.

[Zoheb N]

well you know you can also go with a four wheel four motor design.

We have used crab drive for about the last 4 years and have averaged 3-4 motors on 4 wheels which has worked great.. it has given us a lot of mobility but not too much strength but it is a sacrifice you make in order to get more speed to dodge your opponents

[Peter Matteson]

It really depends on a few more factors. I suggest looking up the 2wd vs. 4wd threads on this message board where we have discussed the advantages and disadvantages of each system.

My current feeling is that a 6wd system with a offset middle wheel is easier for a driver to learn to control. Either way though my team will use at least 4 drive motors.

[Kevin Sevcik]

Originally Posted by DjAlamose

Well, 6 wheels is much better than 4 wheels if you plan on getting up ramps (these would be on other robots). 6 wheels also will give you more traction on the playing field. Having 4 wheels makes things easy to design and build. So there are trade offs between the two.

As for motors, you don't need 4 motors with 6 wheels, 2 would be just fine. When selecting the number of motors you are looking to see how much power you want. The more motors, the more power, the more complexity.

So 6 wheels is more complex than 4, but has better qualities. And 4 motors has more power and more complexity. It all depends on what you and your team feel comfortable with designing and building.

Personally though, I would go 6 wheels and 4 motors.

6 wheels doesn't mean more traction than 4. It only means less force per unit area trying to tear up the carpet. The main advantage of 6 wheels is that they can turn better than 4 wheels, since in a 4 wheel design, two of the wheels have to sideslip somehow.

[DjAlamose]

You do make a valid point. I was only thinking in terms of contact area alone.

And this is why I design arms.

[Lil' Lavery]

It will depends on what you want your robot to ultimately do. A 2WD will grant pinpoint turning (although sometimes bordering on hard to control), but will typically also make it easier for other robots to rotate your robot. Depending on the style of a 2WD, it may also make it hard for you to travel up inclines or steps. A 4WD's turning ability is heavily dependent on the placement of its wheels. The wider and shorter the wheelbase, the better it will turn. A shorter wheelbase also helps prevent you from bottoming out (one of the largest issues with 4WDs and ramps), but a shorter wheelbase also means the robot is less stable in that direction, and thus easier to tip. A "co-planar" 6WD (all 6 wheels in contact with the ground at the same time) is essentially the same as a 4WD, but it helps prevent your robot from bottoming out and spreads out the weight distribution on the wheels. A 6WD with an offset wheel (so that the robot "rocks" back and forth between two sets of 4 wheels, the middle staying in contact with the ground) helps turning (by effective shortening the wheel base) but provides the stability of a longer wheelbase.
2 motors are simpler, lighter, and cheaper than 4 motors in a drive-train, but also provide half the power (assuming all 4 motors are the same). Drive power is typically a premium in FIRST bots, and especially considering the wide range and large quantity of motors available this year, I'd heavily suggest using 4 motors.
Seeing as you're a rookie team, I'd advise you to create a simple, yet fast and powerful, drive system. Consequently I'd advice you to use a 4WD with 4 "Small" (2.5") CIM motors.