I’m just curious about 6 wheel drives… will it make my robot drive faster??
I currently have a 4WD with the back two wheels omni wheels and front two wheels as normal traction wheels.
Should i make it a 6WD and then make the front and back wheels omni wheels with the middle two being traction wheels or maybe even friction wheels… what’s the best here?
I’m thinking about 6 motors to make the robot faster, but looking at the picture below the robot had a 6 wheel drive but the two front wheels were connecting with a chain meaning they didnt need a motor, so it wouldn’ really make it faster right??
If I want my robot to be faster, what should I do… do I need a 6 Wheel Drive… should i add more omni wheels… do I need a chain?
@Vyx To what extent will it make a difference… having 6 motors… I currently dont have the space to add gears right now… Should I do 4WD all omni wheels… 6WD All omni wheels… or 6WD the front 2 and back 2 are omni wheels and the middle 2 are traction… which one?
In that video I am pretty sure that the middle wheels are there for traction when parking on the platforms. If you use omniwheels on the front and back you can use traction wheels in the middle without losing any of the turning abilities of the omnis (you do lose strafing).
6 wheel drives don’t make your bot faster. The extra wheels just add weight, but can be used for other purposes including changing the center of turning and preventing getting pushed sideways.
The best way to drive faster is to reduce friction and weight.
@Mark Finley Also in the video they used a chain for 2 out of 3 wheels on each side thus they still only used four motors… Does having six motors (1 Motor per wheel) make my robot more powerful and harder to be pushed sideways or is the chain just enough (as seen in that picture)?
6 motors can power a higher gear ratio, but then there is the problem of controlling it. A test, as suggested, could consist of 2 identical robots, except one has 6 wheels and one has 4. You would race them to a given point over several tests, find the average time of each, and then you have your answer. You can aso look at what gear ratio 3 motors can power compared to 2 motors.
Once again, if you have the designing ability to use the extra motors, then by all means I don’t see a reason not to.
The obvious answer “maximum top end speed” is the wrong one… but it is the one that many teams pursue.
Fast in a robot game is the ability to get from one position to another in the least amount of time. Since the distances aren’t far apart you actually spend more of your time accelerating and decelerating than you do at top speed. Gearing UP gives you higher top speed, but at the cost of acceleration, while gearing DOWN gives you more acceleration. For short distances the lower geared robot will be faster, while for long distances the higher geared robot will likely win out.
The advantage of the lower geared robot is that you’ll likely have more ability to turn and maneuver at low speed… which could be an advantage if you’re navigating about obstacles.
The number of wheels on your drivetrain shouldn’t have a big impact on this… maybe for a very heavy robot it will give a wider area for weight distribution resulting in decreased rolling resistance as the wheels won’t indent into the foam tiles as much… or maybe not.
Where the 6WD setup comes in handy, though is if you “drop” the center wheels a bit lower than the front or back wheels. This effectively shortens your wheelbase, making turning easier as there is reduced wheel scrub. You can also add omni wheels to one, or both, ends of the robot to make turning easy as well. Moving to 6WD will also change the axis about which your robot pivots. Right now, with omnis on the back, the robot likely turns about a point midway between the front wheels. With 6WD that will move back, closer to the center of mass of the robot.
There is no one “best” drive design, but there is a best design for each team. If you don’t experiment you’re not going to find the one that works best for you. Give it a try!
Keep in mind that motor count is independent from wheel count. 6 wheels will reduce top speed and acceleration, assuming that motor count and build quality (friction) are constant. However, 6 wheels will help keep your robot from getting high-centered while climbing. You might find that the hit to speed and acceleration is worth the increased ease of climbing.
As for ways to increase acceleration and top speed, simplify and add lightness. More motors can help, but only if you adjust the gear ratio to make use of the increased torque. Make sure axles are free to spin and not binding. Make sure axles with gears or chains that interface with each other are parallel. Make sure the things hanging on axles are not rubbing against chassis rails or bearings (and use washers where rubbing might happen). If you want to get even more obsessive, you can test individual motors for performance characteristics (there’s a small variation in motor effectiveness between motors, so they are not quite created equally).
There are ways to get a faster robot with software tricks, too, especially when using 393 motors. For 393’s, the biggest concern is making sure they don’t overheat. Track their current RPM with an encoder, and avoid giving them full power when RPM is low or trying to do a hard reverse. High power at low RPM or reverse power at high forward RPM generate a lot of heat very quickly, so avoiding those scenarios will keep the motor cooler for longer and will let it deliver more power over the course of a match. The other trick for doing things faster is controllability: a robot that is easier to drive wastes less time compensating for operator error. Avoid directly mapping joystick values to motor values. The values people want from their motors is more logarithmic than linear; that is, people tend to care less about the difference between values in the 50% to 100% range than the difference between values in the 0% to 50% range. There are various ways to implement non-linear joystick to motor mapping, and I strongly recommend looking into them if you want to build a fast robot that doesn’t spend the whole match correcting for overshooting its marks.