Drivetrain Preference: Research.

4 HS motors on 1:1 speed mode (1.6:1)
4 4" omni wheels

its pretty “standard” and without a “special” robot/strategy, there isnt any reason to sway towards “stronger” or “faster”

4 HS motors on 1:1 speed mode (1.6:1)
4 4" omni wheels

its pretty “standard” and without a “special” robot/strategy, there isnt any reason to sway towards “stronger” or “faster”

I don’t know. I think I would still have to consider 1:1.6 a bit of a speed-based robot. Although maybe that’s just my thinking. Have we seen many “geared down” drives that hold a whole lot of sacks?

At present, our drive is a 6-omni wheel tank drive, powered by four 393 motors at 100 rpm. We have been thinking about speeding it up just a bit, however 1:1.6 may be too fast for our liking. (We do still want to push.)

I’m beginning to think that for our ~12-15 sack capacity robot, a 1:1 with 4" wheels is just the way to go.



We have tried a few different drive systems this year (x holo, 4 and 6 wheel tank, various size wheels, etc.). We have decided to go with a 4" omni wheel H drive system. It runs four 393 motors on high speed direct driving the back two wheels with HS chain conbining the three wheel sides together. We are using two 393 motors running in torque mode directly driving two omni wheels HS chained together for H strafing portion. In the past we have lost a chain in competition and decided to direct drive the wheels and add chain to share the load across the motors. If a chain breaks the only loss would be the front wheels would no longer be driven. It could cause a sack to get stuck under the front wheel. That can be avoided with good driving, but a lot better than losing an entire side and doing circles. :slight_smile:
Our robot is almost all aluminum this year (first time for aluminum, get it, it rocks) and is light enough for us to push well enough with the motors in high speed.

What do you think?..

Sack Attack has been a difficult game for me to gauge just yet. I’m not sure how to approach it after watching games from both my region and from those around the world. I have heard that rescoring is a big factor in games from one region, but in others I have seen rescore attempts easily countered by defense. For me, the game has come down to a big game of chicken. Defending your own sacks is easy if you’re under the trough that you’re defending and the victorious teams manage to score a few more sacks in their trough than the other team, while maintaining their defensive position.

Drive trains relate to this in that they determine a robot’s capability/role on the field. If you’re trying to rescore, it’s difficult to push another robot away that is defending their trough head-to-head. Even from the side, teams that have holonomic capability can put up a fight and it’s a stalemate at best.

Does this mean you want a strong drive train? Maybe, maybe not. You can push people in the open field now, but if you try to push a team head-to-head while they’re between you and their trough full of sacks, they can raise their arm and use the trough as a brace, forcing you to pin them. If you try to go the other side, you have to take a long way around and they can just slip under the trough and the same thing happens on the other side.

Another thought then, why not try pushing them from the side then? Your “strong” drive train should be able to overcome any strafing power, right? This is where you have to look at trough placement. Your opponents have two troughs, one on the edge of the field, one closer to the middle of the field. Which is the most easily defensible? Clearly the one closer to the wall! We’ve already decided that a head-to-head match is still a stalemate at best. If the opponent is defending their side-trough though, a push from the side isn’t effective either. You could easily pin them against the wall and still get only access to half the trough (36 inch trough minus 18 inch opponent in the way).

It seems like pushing may not be the way to go, although sufficient power is necessary to play the same style of defense as I outlined above, though I think positioning is more key than actual pushing power.

So what does this leave us with? If pushing isn’t the way to go, is it speed? This is the direction that my team will pursue in the next iteration of our robot. If I’ve analyzed correctly so far, I feel like making quick forays away from defending your trough to grab a few sacks to throw in, then turtle back down is the way to go. I don’t know if I like the way the game has been developing, but I have a few ideas to challenge the current metagame. But this thread is only about drive trains, so I’ll leave it at that…

Even though I don’t have it I have a design for a shifting mecanum crab drive that is able to go in 8 directions.

I think this is a troll. Adding Mecanum wheels to a crab drive defeats its purpose.

Anyway, my team is going with a 6-wheel (4x 4" omni, 2x 4" traction) tank drivetrain with each wheel directly driven by a 393 motor. It is among the simplest drivetrains to build and has excellent speed and turning and good pushing abilities. It also easily drives over any sacks on the field.

Well, your drive really depends on what you think is the most efficient way to play the game. For us we thought that in the early stages of the game, scoring a small load quick (5 sacks) was the best way to play the game. This is something that made sense for early game play. (We used to have a 1:1.6 drive with 4 4in Omnis).

Like what SweetMochi said earlier, this game is pretty much a game of chicken, should i block, should i score, should i descore, etc. It really reminds me of the isolation zone in gateway, especially the semi 1-1 of the science division 2915 vs 720, it was truly who could trick the other to move. The same game play is being implemented this year. For example “faking” to pick up some sacks, could cause the opponent team to stop guarding their own trough, thus giving you the ability to descore (visa/versa). If your planning on playing this style of trickory/chicken, then a fast drive is the right choice.

On the other hand, some people on my team and others think that aggression and pushing is going to be the right way to play. Kinda like the interaction zone in gateway, if you can push your opponent out of the way, then you can get to the goal that you want to get to. Later in the game we are going to see a lot of teams that score once (1437’s liberator), or score and then block all game (404A’s dumping robot). If your planning on playing with this style of pushing/going to the other side of the field, then a torquey drive is the right choice.

There is clearly no right choice when it comes to drive trains, you have to make a choice based on how you think the best way to play the game is. Based on these observations i hope that you can narrow down what style of play you want to approach, and then choose your drive train based on that. I hope this helped. :slight_smile:

No it’s not a troll. I meant omni wheel.

Why would you have a swerve omni wheel drive?

We are going to soon have an 8 motor 6 wheel drive that has a transmission…

decided to go try something different (works well) … 2 (269 motors) at a 5:7 gear ratio on both sides (4 high traction wheels) geared together.

drive is fast enough and has enough torque to drive intake with 8 sacks in easily

good so far (note previous design was 2 x 369 on omni wheels) . 2 powered directly, and 2 free rolling

Hope this helps :smiley:

wait, so for your ENTIRE drive, you have two (2) 269 motors?

Yes - for some reason it works really well

I have a design for a crab that can do pretty much any direction you want.

Performance idea.

I know Tabor473 has a really interesting drive train that wouldn’t fit under any of the thread’s choices. I might end up copying the Tabor drive because of how well it works. I will ask him if we will post a teaser in this thread.

This year there do seem to be a lot of different drive trains compared to last year.


Are any teams able to run directly driven mecanums with 4 x 393 motors internally geared for speed? We have found we cannot. Strafing seems to overload the motors and can cause them to cut out. Perhaps we are just too heavy at 8.6 kg (19 pounds) ?

Thanks, Paul

I might when I get an entire robot on top of the drive train.

To Torque
Last year at worlds i had a 6 motor 3:2 mecanum drive and strafing was possible but not as good as i would have hoped. A few other teams have had issues with fast mecanum drives because of the canceling vectors involved.

We were able to do so without a problem last year. Video.
Our robot was very light, though. My guess is 12-13 pounds.

We had a 4-393 mecanum drive on torque setting, with a similarly weighted robot. Although the drive worked reliably, and it was able to play good defense, the weight of the skirting that was needed to stop mecanums from getting caught on sacks made the robot slow and ungainly. So, we decided that a light, speedy tank-drive robot is better for offense than a slow-but-holonomic one.

I would like to point out that this was not me -_- we have an impersonator on the loose :open_mouth:

Just thought i would clear that up incase it strikes again… this one has a . on the end of the name, the real me doesn’t :stuck_out_tongue: