NEW DRIVE TRAIN with Vex Pro Gear Boxes

Secret City Wildbots decided to test the new Vex Pro Ball Shifters and we love them! We can accelerate up to 24 ft/s, and in low gear we’ve been able to push up to 240 lbs of dead weight.

Here’s a video of our first test:

What size wheels are you using and what is your gear reduction after the transmissions?

We’re using 4 inch high performance aluminum wheels with blue high traction tread. Regarding gear reduction, here is the info directly from the Vex Pro website

Gearbox: 2-Stage
Overall High Gear Reduction: 3.667:1
Overall Low Gear Reduction: 8.333:1
Spread: 2.27x

Yes, but do you have any additional reduction from the output shaft to your wheels? What sprockets are you using on the output and your wheels?

They’re moving about the same speed we were when we arrived in Bayou last year and couldn’t turn. About 23 feet per second. I assume they are just direct driving off the gearbox.

Luckily they caught it before they arrived at the regional…and dont have to scavange for parts to rig up a (award winning :wink: ) coaxial drive system.

Actually, I’m not certain they think being geared for 24 ft/s is a problem. I suspect it will become more apparent as they add weight to the robot. Luckily, low gear will put them right around 10-11 where things are a little saner.

We didnt even notice it with weight.

We didn’t have carpet to practice on at home so even on pneumatic wheels we were turning on linoleum. Carpet DESTROYS dreams.

To the team in question:

A CIM spins at 5280RPM, 88 revolutions per second. If you are direct driving with your gearbox and 4 inch wheels, you are driving at about 23 feet per second. Much too fast. anywhere between 13-17 is considered “normal” in FIRST (high speed).

Last year we did the same thing on accident, and once you throw 100+ pounds on top and try to turn on carpet it becomes a HUGE issue going 23fps. We had to cobble together this ridiculous setup. Instead while you have time, I would suggest building some offsets for your gearbox, and either put another gear reduction stage in there, or use sprocket reduction.

Yeah, we’re a second year team, so we haven’t had much experience driving in competition . Realistically (as I learned the hard way… I’m sure my team is thankful I’m not going to be a driver), it’s hard to stay in control moving that fast. We’ve got a 6 wheel center drop, so turning doesn’t seem to be an issue. Would it be?

The issue isn’t the wheel pattern, its having the torque to turn 120+ pounds.

Put it on carpet and I’m sure you’ll notice a huge difference. And like the guy from 57 said, your low speed will work, and seem easier to control. Other things to consider are robot-to-robot interaction, and the fact that youll never really have room to accelerate to that speed.

If i understand correctly, I believe that when you’re moving that fast, your drivetrain has less torque. A drop center 6 wheels minimizes wheel scrub, but a fully weighted drivetrain still needs a certain amount of torque in order to turn. the faster you’re geared, the less torque you will have, and there will be a point where your drivetrain is unable to turn under the weight of the rest of your robot.

If I were you guys, i would recommend increasing the reduction from your gearbox to your wheels. You could either purchase the optional 3rd stage from vexpro, or increase the sprocket size on your wheels.

I didn’t realize that weight would affect things so drastically! We have the 3 stage, we just didn’t mount it. We’ll talk about it tomorrow. And we have been testing it on carpet. The video we posted was on the carpet in our green room. We will keep our eye pealed for potential problems, thank you!

Not that I can see the actual weave of the carpet in the video, but I think that style/pattern usually goes with a somewhat shorter and tighter weave than what we drive on in FRC. You might see if you can buy some carpet that closely matches the FRC carpet and try driving on that with your robot weighed down some more.