Fast wheel base

Any suggestions for really fast wheel base with only 4 motor drive… Would be helpful to give ideas of robots can also quickly side to side as well.

If you want to move from side to side, A X-Drive is going to work. But X-drive is very slow. If you are using a normal driving base with one extra wheel horizontally, it would work. But it will need at least 5 motors

A X chassis with all wheels at 45 degrees with turbo geared motors.

The issue with trying to go fast with 4 motors is them burning out, especially if you are a heavy bot or are attempting a quick turn or something similar to that.

Most people will use holo and most likely all the spare motors will be put in drive once all the other mechanism have been allocated motors. The faster the better as this game will be fairly fast paced.

Thanks guys for the input… Greatly appreciated

Fair warning about a fast drive base: you will want slew rate control. We used a 6 motor drive on 3.25" wheels at 320 rpm free, and the safest way for us to turn around while we were going forward was slamming into a wall at full speed. That still broke motors, but less than if we just turned or went backwards.

As far as a fast 4 motor drive, I’d go with an X-drive and a light robot. For whatever reason, according to AURA’s math and experimental observation (Google “shifting X-drive”), an X-drive is actually faster than a tank drive by a factor of about sqrt(2). However, this does not apply to mecanum wheels, which are extremely slow. Does anybody know if mecanum wheels increase torque or do they just bleed power?

We actually used mechanum this season (mistake) because our 4 motor omni wheel drive couldn’t hold our robot based on its heavy weight. We ended moving much more easily with the mechanum wheel but as u said they are much much slower

If I somehow built a 12 pound robot with a catapult (I haven’t, and don’t know how to) how would I keep the robot from jumping or flipping upside down?

Anti-tip bars. :slight_smile:

@technik3k had a great idea last season for that issue. Mount the entire catapult on a pivot (HS axles, anyone?), then hold it down with rubber bands. When you shoot, the catapult’s energy will dissipate over time, rather than exerting a point-load. It might introduce inconsistency, but I think the rubber bands will help solve that. Also, if you use HS axles for the pivot, attach HS gears to the axles, then gear an encoder up off it. That will tell you a lot about the catapult’s motion.

There was a cool infographic that someone was posting a while back. It would seem to indicate that mecanum wheels do indeed increase the output torque in a similar way to omni wheels increasing the output speed. In some ways, the vex mecanum wheels are a ‘dumbed down’ version of the real thing, as ‘proper’ (like the ones in the Vex PRO lineup) mecanum wheels offer better speed and torque output and are much smaller.

This is quite a cool team that was doing a variable x drive to change the amount of torque and speed output of their robot:

Exactly

Inconsistency this year won’t matter nearly as much as it did in NbN since you have a 12 foot range target.

Well, yeah, but you still need to shoot high, and even higher against a wallbot. And with game pieces that bounce really weirdly (think an American football times 3), getting objects to stay in the far zone will be a challenge in itself. And you need the rubber bands anyway to provide resistance and force the catapult to decelerate.

And, getting this thread back on track, the key to a fast drive will be a light robot. If anyone watched the Vex U matches over the last few days, you probably noticed that the small robots were usually much faster than the larger, heavier ones. Heavy robots require more torque, more torque requires less speed or more power (power = torque * speed), and we have the same amount of power available for a light robot as a heavy one.