Asterisk Drive for Spin Up

VEX Robotics Competition Discussion VRC > Spin Up (22/23)
1

With the new game, I am interested in the ability to strafe.
Being able to strafe is useful with:

  • Quick repositioning
    • Avoiding other robots
    • Finding the best real estate in the endgame to start to expand
  • Strafing while simultaneously facing the goal to shoot, such as traveling in a horizontal arc (faster scoring)
  • Increased agility in gameplay
  • More creative routes in skills match

However, with many teams declaring their use of 6 motor drives for the Spin Up season, I fear that the traditional x drive (using 4 motors) would not be able to survive amongst the more powerful drivetrains. However, I am confident that strafing is an advantage in this game due to the reasons above.

Thinking 4 motor drives to be lackluster, I set my sights on a drive with both strafing and more power. In my research, I came across the asterisk drive. Using the traditional layout of a 4 motor x drive, it adds the ability to be more offensive with two wheels oriented on the flanks of the drive, arranged in tank style. This 6 motor drive, is stronger than a 4 motor drive but it does not compromise the ability to strafe.

To make this work, I decided to use a combination of drive ratios.
The wheels in the x would be set up as follows:
2.75" omni wheel, 300 rpm (600 cartridge geared 1:2)
The two tank wheels would be set up as follows:
3.25" omni wheel, 360 rpm (600 cartridge geared 3:5)

Attached below is an image of the drivetrain I envisioned.

Asterisk Drive
Asterisk Drive1920Ă—1080 333 KB

The linear speed of the x wheels would be 40.73 in/ sec, and the linear speed of the tank wheels would be 41.89 in/sec.
The drive program will be adjusted to account for the slight difference of 1.16 in/sec. in linear speed between the two wheel sizes.

To easily picture this drivetrain, imagine the speed of a 3.25" 360 rpm 6 motor tank drive, with the ability to strafe.

To facilitate this discussion, I will list my compiled pros and cons of this drivetrain.
Pros:

  • Strafing
  • Increased forward pushing power for match play (compared to standard x drive)
  • Combining the agility of x drive with strength of tank drive

Cons:

  • Extra 2 motors might be better used elsewhere
  • 2 tank drive motors not always driving (e.g. when strafing sideways), so wasted motors in drive
  • Still less torque than a tank drive with similar speed

I wanted to ask the community: is this the right design choice? Is there a better solution, and is strafing less important than I think? Is this drive overly ambitious, and the tradeoffs are not worth the benefits?

Resources to familiarize oneself with asterisk drive:

25 Likes
2

like why would you do that though

1 Like
3

I don’t think six motor drive would be the meta in spin up. For me, I would rather build double intake and a very strong shooter.

4 Likes
4

could honestly be a viable option, as I expect 6 motor drives will be the meta this season, because now people know just how nice 6 motors of pushing power is, and because I seriously doubt the meta will necessitate 4 motors just for scoring.

And I can’t think of any better ways to achieve a 6 motor holonomic drive, though maybe a similar layout but with straight mecanum wheels on the outsides could offer similar performance.

But of course, there’s always the issue of any sort of holonomic drive typically being not worth the effort unless a team is prepared to put in a lot of programming work and driver skill into properly utilizing it, which would hold true for this drive as well.

10 Likes
5

While I do like the idea of adding extra speed to a drivetrain, I think this drivetrain would not be sufficient for winning matches. First up, any team using this design will have to sacrifice 2 more motors to speed. In most Vex games such as Tipping Point, the task could be accomplished with 2 non-drivetrain motors. for Spin Up, an intake and flywheel are already 2 motors, and a team would have to find a way to use pneumatics to control the roller or give up on it and the AWP entirely. Secondly, it only adds to forward and backward speed. Considering many teams are looking to score in the high goal, A bot would likely be facing it at all times. Because of that, Forward and backward motion and side to side motion would be pretty even in use. Since an Asterisk Drive focuses on forward and backward speed, It wouldn’t be able to fully utilize those extra 2 motors for roughly half of the movement. Finally, a speed increase wouldn’t be very helpful. Since bots will have a delay between picking up a goal and shooting it, Many teams would drive to the next disc while shooting to save time. Even if you can get to disk faster, your shooting mechanism would have to keep up while only having two motors to work with. While this idea has many flaws, I would like to see someone try it out and see if it could be a valid design in practice.

3 Likes
6

I agree, I could see mecanum wheels becoming more of a meta as they give both side to side and forwards to backwards movement. It would take less motors, but it would take more coding and weight.

7

I don’t really agree with the flywheel requiring two motors, one motor could do the job. Even with the longer spin up time, this would be sufficient enough to shoot the disc across the field.

As proof of concept for a two motor intake and flywheel, check out Purdue’s early season reveal. It is a good example of a bot with 6m drive.

The two tank drive motors would serve the purpose of adding pushing power. I envisioned that this drive would be able to thwart opposing alliance’s scoring by ramming or pinning. Ramming another bot would be done primarily by going in head-first, utilizing the 2 tank motors. Pinning would also utilize the two tank drive motors, since most pins are done with the front or the rear of the robot.

While I agree that the sideways strafe and the forwards movement would be relatively equal in use, the strafing movement does not necessarily need the power of a 6m drive, while ramming another bot head-on will.

While having a similar ramming power of a 6m tank drive, this drive adds strafing. Arguably, this would be an advantage in match play.

4 Likes
8

Aren’t mecanum wheels bad? I asked in several discord servers and read up on forum posts, and the majority consensus agreed that mecanum drive is inferior to X drive. Do you see their performance as being relatively equal?

9

they do seem to be generally disliked, but I will drop this here:

clearly, they can be good in the right hands.

the main complaints I’ve heard of mecanums are their bulky size, and their reliance on having a very good center of mass for the strafing to be reliable and straight. But I don’t think center of mass is going to be much of a problem with this game, and back in TT when center of mass was worse than it ever was, 7k was able to make them work.

I have no personal experience with either though, as I knew I wasn’t going to be able to make good enough use of a holonomic drive for it to be worth it.

6 Likes
10

like why would you make lifts out of polycarb

:joy:

10 Likes
11

I think they are as Xenon27 mentioned, great in the proper hands (probably not mine haha). I think the real benefit will come from being able to move “just a bit” to the right or left to line of the shot. I have had some positive experience with them but haven’t used them in a competition setting. I am excited to try them, and if they don’t work, I can switch them up. :smile:

12

i was spoken to in a dream by the polycarbonate

3 Likes
13
26 Likes
14

Update: my initial calculations were incorrect.

The correct values would be:
x wheels: 61.09 in/sec
tank wheels: 61.26 in/sec

My bad for not double-checking my math. Credit to @seenSeal for noticing.

7 Likes
15

For a 6 motor drive+turret, the turret could possibly be spun using motor sharing mecahnisms and differentials

1 Like
16

it is also a lot slower right? i guess strafing isnt as important when you dont gain the speed advantage of a tank drive just turning and driving faster

17

I am planning to use an asterisk drive, use one motor for a constantly spinning intake & flywheel, while the last motor would be used for an indexer with a ratchet that would spin another roller mech. The only thing im worried about is if one motor is strong enough to power the flywheel & intake, and if I accidentally intake extra disks since the rules say the max is 3. I could probably use pneumatics to make a cover for the intake which would stop unnecessary disks while the intake is constantly running.

18

Yes, mecanums are naturally slower than X drives because of the x drive’s strafing nature (mounted at 45°, sqrt 2 speed)

However this can be mitigated by gearing up mecanum wheels.

image
image1399Ă—1039 247 KB

This is an example of a 257 rpm mecanum drive, courtesy of Alex from 20203Z

5 Likes
19

Can you tell me which gears (how many teeth per gear) are used in here, and in which order from motor to wheel and what cartridges would need to be in the motors for this to go at 257 rpm.

20

3:7 600 rpm (36:84)