With regionals and worlds coming up in a couple of months and most teams being in the rebuild stage of their robots right now, I thought I would pose the question of whether speed or torque will be more important in a chassis at regionals and worlds. Obviously you want to be able to score the field balls as fast as possible, because if you have the advantage in field balls then you have the advantage in the game, but there will also be quite a bit of defense played, so a chassis that is too torque deficient will get pushed around a lot and possibly stall. What are your thoughts? Will it be better to gear your chassis close to 3:1 to out maneuver and out run your opponents or gear your chassis somewhere between 1:1 and 2:1 to be able to simply plow through your opponents and play a little defense.
Also, I accidentally posted this in technical support :/. If anyone could change it to general forum that would be great.
My team decided on torque, there are a number of reasons for this
- we focus on full court shooting, so for that aspect of the game mobility isn’t important
- we have a lifter, so we need to be 100% sure we can get back to the climbing zone at the end, having torque drive (and specifically our drive) means that we can shove anyone out of the way to get to the climbing zone
- most field bots, no matter how fast, only shoot effectively from2 spots, mid field and point-blank, so blocking them is easy, we know where they will go, so being their first is easy. so what my team tries to do, is we go and get 1 or 2 balls, while the other faster team get 4, then we sit in their shooting spot and score our balls while, at the same time, blocking our oponents
Just look at the first match from this video to see why faster robots can score so much more that ones with higher torque. They’re just to fast to be blocked!
Also, trying to block a fast robot is quite difficult, because they can go right around you. And if you stay in their ideal firing position to block them, you wont be scoring at all, while they’re still scoring a bit. I agree with @Collin Stiers that the only way to get back to your starting tile if they’re blocking you it to have a torque drive though. Although they take more resources, the best drives, in my opinion, for any year, have transmissions.
That reminded me of a match I saw recently on youtube. I think it was one of the finals matches in Ontario. Unfortunately the video got taken down, so I can link it in here, but basically the 2 really good 1104 teams went into the field before shooting their driver loads and one of the robots on the other alliance almost succeeded in keeping BOTH of them out of their loading zone. One of them just barely squeezed through with enough time left to get all of their driver loads shot off, but that shows just how important it is to have a chassis that can get you back into your loading zone and how important of a strategy defense can be.
I propose this as a counter point. In this competition we had a bad shooter encoder that really decreased our scoring ability (although we didn’t know it was the encoder at the time) and we were facing the 1st seed alliance which had the very fast and very high scoring 24B, we knew that we couldn’t out score them and we knew that if they were allowed to score we would loose, so defense, we reduced their score to probably 10% of what it could have been, and the only reason they scored anything at all is because we were letting some new drivers get some experience, had it been our main drivers, I’m confident they would have score almost nothing
Here’s an idea I had a couple weeks ago that could be the best way to combine torque and speed without a transmission. I’m not sure if it would actually work but I might try it out if I have the time. Basically the outer 4 wheels are internally high speed geared, plus the 1.4:1 speed boost you get from x drives gives the chassis an overall gear ratio of 2.24. Then there are the middle 2 wheels which have a 1:2 gear ratio geared for torque. These wheels would be on a ratchet so that when the robot drives forward full speed the torque wheels don’t slow it down, but when there is a robot in it’s way it can use those 2 torque wheels to push them aside with ease.
I don’t remember which video it was. All I remember is that one of the robots said “Feed Me” or something like that, and the video was removed a couple of hours after it was posted.
I really like the idea of this, but even though it’s geared down for torque, It’s still only two motors pushing against an other robot with half as much torque, but twice as many motors. I would still like to see this go somewhere though.
Also, wouldn’t the holonomic drive decrease the speed you go at, since the force is being applied diagonally instead of linearly?
It actually increases the speed by root 2 (~1.41). I am not sure exactly why, but there have been quite a few post about it in the forum and I know it has something to do with the 45 degree angle and how it relates to a 45 degree right triangle (which has sides 1, 1, and root 2).
they should logically slow down the robot, if you draw out the triangle, where the hypotenuse is along the axis of the wheels, then the shorter legs will be in the X and Y direction, so Sin(45) = sqrt(2)/2 and so you get about .7, or 70% of the force in any axis
Exactly what I was thinking too. But this website seems to agree with @Michael Nutt.
http://botsnstuff.com/wiki/X_Drive
Can someone please explain, or link to a full explanation of how this works?
That link and this one were the two that I found earlier this year when I was trying to decide on a chassis design.
Cool, thanks.
Now this drive train seems even more functional:
It acts as a really cool transmission.
ok, now let me check my reasoning here it see if I really understand
if I get this then mecanum wheels should not benefit from this same effect, is that correct?
also, has any one tested this on a real robot, because the diagrams shown there are odd to me,
http://www.aura.org.nz/archives/1137
if we look at the diagrams here, the X drive is rotated 45 degrees from how we normally would think of it (here it is more + drive than X drive) if we rotate the drive back the way it normally would be in my mind, and then we draw the X and Y force vectors for each wheel, we would see that all the X force vectors Cancel, leaving only the Y vectors, and a slower speed with less force, so jut by shifting perspective the answer seems to totally change, I will continue to think on this
I don’t think that adding motors adds any speed, just torque.
Hmmm… I think I’ve come up with a way to get around defensive robots. I’ll have to test it out tomorrow, but basically what I am thinking about is using a sort of “spin move” to get around them. If it works I’ll post a video of it.
I think the best way around defensive bots is to keep going about your business (being mindful of the other robot obviously 
). The only way to do this that I can think of is to have a turret. If a robot is pushing you out of aim, the turret moves to compensate.
So theoretically a really good anti-defence bot would be an auto-aiming turret with a auto speed adjust and a high speed X drive. It wouln’t matter where the defence bot pushed you, as long as you can pick up balls all is well.
That’s a swerve drive. The tough thing about that style is the number of motors it uses. Chaining together the swerve part to use fewer motors is ideal but the strength of the vex motors makes you typically use more than one. So now you have six motors assigned to your drive.
It can be deadly effective since you get the full torque of all your driving wheels all the time. It can be a bit tough to drive though and takes some practice unless you use a gyros and either IME/quad or a pot to control the steering direction. Team 1640 has been using the same one for five years now in FRC with incremental improvements each year.
Couple this with splines to make a curved driving path and that is one deadly bot. (that uses 6 motors for the drive)