Asterisk Drive

I was looking around, and I haven’t seen anyone use this base before, so I titled it Asterisk Drive. If someone has already named this base, then I will call it by that name. Otherwise here is Asterisk Drive:

We came up with the idea for this Drive Base when I tried to combine an X-Drive and a Tank drive into the same base.:eek:

The result was a 6-wheeled, 6-motored, high speed holonomic base. It has all the functions of an X-Drive and a Tank drive, giving the pros of each base while eliminating many of the cons.

Ours has the effect of a 1.6:1 speed base, utilizing 6 motors. All of the motors are internally geared. One could use any gear ratio they want with this base. For example, someone could easily install a 2:1 gear ratio for more speed.

Technically it isn’t a perfect gear ratio. The 4" wheels are running on a 1.6:1, and the 2.75" wheels are on a 1.56:1. This will not effect the base since it is only 0.04 off and it has preformed well in testing so far.

Since the 2.75" omni wheels were out of stock for a while, our have been ordered but not delivered yet. Please excuse the fact that two of the wheels are missing.

Here are the Pictures:

Asterisk Drive got it’s name from the combined vector angles of each homologous pair of wheels. Since the X-Drive was named in this manner, I thought Asterisk Drive should be named in this manner as well.
The shape of the vectors makes a Asterisk (*) shape. See picture below:

See this part of our website for more pictures and updates: https://sites.google.com/site/haslettvexvortex/robot-progress/the-base

I remember someone calling this drive scorpion drive on bns

It was something that Jordan and Andrew were working on I think. The scorpion drive.

Unintentional design convergence. I found this but that was all I could find on anything called scorpion drive. We have been working on this project for a few weeks. I respect the members of bots ‘n’ stuff, so if you have a logical reason to call it scorpion drive, I will call it that. Just I don’t see any relations to scorpions in this drive.:confused:

Anyway, I don’t know who cam up with it first. I looked around, couldn’t find anything on it, so I thought it was an original idea. BNS is a private Skype group, so I have no idea what ideas go on around there.

Pretty much, if Jordan is working on one two, I know I’m not crazy for trying this.

Please, I would like to know why you decided to call it scorpion drive.:confused: I don’t want to sound conceited, but Asterisk Drive has reasoning behind it. Plus, I don’t know if anything went on, but I told a couple Bots ‘n’ Stuff members about this a few weeks ago.

How long have you guys been working on this?

Cody Smith (now with VEX U team NAR) had dubbed it the “Scorpion Drive” in this post, which was the first time that I had seen this type of a drive design. The images appear to be down, but it was essentially the same idea as what you have built. I believe that his design had used all 2.75" wheels.

This was actually a different design. It was similar, but essentially was a drive that could “morph” between a scorpion drive and a 6-wheel tank drive. Hence, Andrew and I had decided to call it the Morpheus Drive.

Ok, Thanks. I didn’t see that post, and the pictures are no longer available for viewing. Perhaps I would ask Cody why a scorpion. I believe this is an easier base to work with though. The straight 4" wheels, to the 45° angle 2.75" wheels is almost a perfect gear ratio. I would like to call it asterisk base, but Cody likes his weird names for things: scorpion, hipster, etc… Unless of coarse there is a logical reason behind the scorpion part.

From his post, this was about all he said about it:

Yes, I get the fact that the name scorpion does sound cool, but it doesn’t describe the base the base at all.

Besides, mine is slightly different due to the fact that the base is still a square. It features an open front, just like other U-shaped bases. Therefore, while a scorpion has 8-legs and cody’s base was an octagon, that makes sense. My base is not an octagon, and the wheels are not the same size.

In a similar manner, a 4-bar and a 6-bar are similiar. They have a similar function, serve the same purpose, and are powered the same way, but are built differently, so they are considered different lifts. The scorpion base and the Asterisk Base have similar function, serve the same purpose, and are powered the same way, but are built differently, so they are considered different bases in my opinion. It’s hard to say for sure since the pics have been taken down, but personally I consider them different bases. You can disagree with me, that’s just my opinion.

You can’t say that they are different because your framework is a square instead of an octagon on the outside. is an X-Holonomic and https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcSpqr26Npm67EBhopG8Yy0Luyxuwh6IJd2pUEenKkgAG1YdwhhKhg is an X-Holonomic, different shape, same function, same name, please don’t make stuff to complex with adding a cool little “this is mine” name.

Also, a 4-bar linkage is named differently from a 6-bar lift because of the number of bars used in the lift (dur), which is actually explainable.

Honestly Vex Vortex’s name isn’t a this-is-mine name, in my opinion Asterisk drive is more fitting than scorpion drive. Like X and H drive, “Asterisk drive” is a name that describes the wheel placement/layout.
If you don’t want to use it then don’t. If the name helps people and makes sense then they’ll use it and it’ll catch on.

Hi guys!

I… don’t seem to have those images anymore. I do remember the design. It was a concept drive, never got built.

This drive’s big negative is that the outer wheels, the ones in the X config, end up moving faster than the wheels on the sides, see this for details.

I actually got this wrong initially. I don’t really fact check most things, I just picture them in my head and think about it. My logic was completely off, but those guys set me straight.

Anywho if you build this you’ll need to programmatically slow down the X wheels by about 40% (technically 41.42135623730950488%), or root 2 minus 1. If you want everything to be OK.

I suppose technically running the outer wheels faster may not be an actual problem in the real world as they would just try to drag the side wheels with them, but on paper they are going to go faster and cause problems.

Turning however will NOT require any speed change as long as the center of all the wheels are the same distance from the center of the robot (basically so long as the wheels are positioned tangent to a circle centered on the robot’s CG). HOWEVER, with six motors this robot is going to turn quick, for your drivers sake I would use a log curve or something like that.

This however will require some slightly interesting programming since the equation for how fast the wheels need to go is different when turning.

Also interestingly there’s no limit to how many wheels you can have in this tangent to a circle configuration. It is possible with the right math to solve a speed for each wheel regardless of where it is.

Anyway, from a tactics perspective I’m not sure anything is gained by the extra wheels. You’re paying for the weight of the framing, wheels and the complexity involved with building and programming this. I’m just not sure if there is anything to be gained. You could just as easily put two motors on the front two wheels if you want the extra torque. Or two motors on all four wheels if you’re crazy like Andrew and I.

And yes, technically I did name it the Scorpion drive years ago, but really who the hell cares? Call it whatever you want, just remember the Hipster drive is too cool to be renamed. :stuck_out_tongue:

SO YEAH, if someone wants to build this, I’d be willing to help with the code to drive it. It’ll be a slight modification of my x-holo code from way back when, shouldn’t be too hard.

-Cody

Thanks Cody. This is why the middle wheels are larger. Larger wheels spin faster due to a larger circumference. So actually, no power limiting is necessary with my base. Strait 4" onmis, to 45 degree 2.75" omnis is a: 1:0.98 gear ratio. I used a lot of math ahead of time to make sure the base would work first.:wink:

Right… picture, I didn’t see them, the inline images seem to be broken.

So, let’s check the math real quick. I’m assuming based on the picture that there isn’t any gearing between the motor and the wheels.

We need the straight wheels to be 41% faster than the outer ones…

2.75" wheel @ 100 RPM
2.75 in x 1/12 ft/in x 3.14159 x 100 RPM x 1/60 min/sec = 1.20 ft/s

Target speed of the straight wheels (-)
1.20 ft/s * sqrt 2 = 1.70 ft/s

4" wheel @ 100 RPM
4 in x 1/12 ft/in x 3.14159 x 100 RPM x 1/60 min/sec = 1.75 ft/s


2.75" wheel @ 160 RPM
2.75 in x 1/12 ft/in x 3.14159 x 160 RPM x 1/60 min/sec = 1.92 ft/s

Target speed of the straight wheels (-)
1.92 ft/s * sqrt 2 = 2.72 ft/s

4" wheel @ 160 RPM
4 in x 1/12 ft/in x 3.14159 x 160 RPM x 1/60 min/sec = 2.79 ft/s

The numbers seem to work very very well, cool!

However there is still a little issue that must be solved in code. You only get that sqrt 2 advantage on the X wheels while moving directionally. When you’re turning all things are equal and as it stands that means your outer wheels will be going (assuming 100 RPM) 1.20 ft/s while the straight wheels will be going 1.75 ft/s. Simply slowing down the rotational component of the input on just the straight wheels will fix this. Luckily you get the most power when rotating so losing a little on two of your six wheels won’t be an issue.

-Cody

Are you viewing it on mobile? If so, I posted them on our team website which has a separate mobile website. That might have messed with the website link. I know it doesn’t show up on my phone.

Yup! I did a fair bit of work with the math. I was calculating the speed of our X-Drive a while ago and came up with some numbers I could work with. The result was the idea for a six wheeled holonomic base.:slight_smile:

We have a pretty good programmer. I tell him what I built and what I want it to do. He usually comes up with a solution. He’ll figure out a way to have a separate turning function.:cool:

Thanks for all your input by the way. I appreciate constructive ideas and help.

You’re quite welcome. Good luck.

Thanks. Our wheels just came in so we should be able to finish this soon.:slight_smile:

Oh btw Cody, I saw a robot at the second scrimmage with a hipster drive! The wheels weren’t completely 45 degree angles and so they were able to turn but by god it looked like a sad robot. Just thought I’d let you know it’s been used, possibly from the thread :stuck_out_tongue:

I’ve deleted one post from this thread for being inappropriate.

Thanks Karthik. We appreciate everything you do for the community.


So what are people’s thoughts on the base. Suggestions to help us improve are great.

Here is the video of the first ever BUILT Asterisk-Drive. I made a video on the base, and it’s working.

It can be found Here:
https://www.youtube.com/watch?v=cinJ-xmWA1o

Thanks, Feedback and suggestions are helpful.:slight_smile: