4418’s off-season chassis design consists of modifications to the 2015 kop chassis. I tried to keep it as simple as possible for manufacturing by limited the parts I used to materials my team is in possession of or readily available. It is a fully omni-directional and features a dropdown plaction wheel for high torque situations. It is not a wide chassis but a long one as the center omni and plaction wheels would do the most driving. The 4 omnis at the corners are for strafing and turning on the pivot the plaction wheel acts as when extended down. The single cim attached to each mini toughbox are hidden for so they do not obstruct the view of the center structure.
Have you considered the loss of traction you’re going to get by only driving one of the wheels in the primary drive orientation? At best, the robot’s weight will be distributed between the single primary wheel (whether omni or plaction) and two of the side omni wheels. This will reduce the amount of force you can apply before the wheels start slipping, meaning you won’t accelerate (or push, if that was a consideration) as well as a drive system where all wheels are driven
Nice drawing. Your design looks interesting, but I’m not sure how you intend it to work.
When traveling forward are you able to lift both ‘H’ or transverse drive wheels or will one wheel always be in contact with the ground?
When traveling sideways, it seems like the driver can choose to use the omni wheel or the traction wheel. How about when moving on a diagonal?
The traction wheel may hinder movement in that direction. it would be worth testing.
I believe team 148 used a pneumatically deployed omni wheel a few years ago. Are they around to comment?
In 2015 we built an ‘H’ drive for the first time. Tried it out on a practice bot. It was cool seeing a bot move on a diagonal! We used spring tension to put weight on our wheel. If we were to do it again, I would try a pneumatic approach and use the regulator to adjust the wheel force.
Never saw this type of drivetrain before, but I think the intent is to have two modes: one where the DT is basically a H-drive, and another mode where the direction of the strafing module is your forwards and backwards, and the omni wheels on the side rails are used for turning about the traction wheel.
This is getting somewhere, but there are some issues with the strafing module. The first is the placement of the pistons: from the image, it looks like the pistons are going to prevent mounting the drive motors to the gearboxes.
This also reminds me of something I made in the past (link is here: http://www.chiefdelphi.com/media/photos/42457)
The way I mounted the pistons on the wheel pods were questionable, for if the robot were to be hit on the side, the shaft would wear and even bend after a few rounds of pushing and shoving, and the pistons wouldn’t probably last too long. The DT you made may have a similar issue, so I’m thinking you can fix that problem by having two face-mounted pistons, perhaps using a smaller stroke, and these two basically push down on the module rather than be mounted by a clevis. This way, the pistons won’t witness much of the impact force in pushing matches.
Otherwise, this DT is looking good, and do try to improve on this: I’m pretty curious myself where progress on this goes, especially because I’ve never seen this type of drive before.
Why not start with the AM KOP chassis in the long configuration, replacing the regular wheels with omnis, and put a drop down strafing wheel there? It seems like that would be more advantageous, since you would have more wheels contacting the ground, and more driving wheels in the same direction. It seems that that would be better for your intention with the robot. Also, those two cylinders (ie: “pistons”) in the middle of the robot might be a serious problem depending on the game, as they intrude on prime real-estate for manipulators (in addition to Dan Koh’s mention of them getting in the way of motor mounting). Definitely a neat idea, I haven’t seen a lot of people do this with the KOP drive.
This is going to be a long post, so I’m going to split it into sections here.
This by all means is a “H” drive. That term has already been coined and more people will know what you’re talking about, so do yourself a favor call it an H drive. I would suggest reffering to this concept at the “KOP H-Drive” from now on.
Here’s the meat and potatoes of my post. This concepts lends itself to a very unique driving strategy, one I’d like to demonstrate with hypotheticals then comment on.
-Assumptions. For clarity sake we're going to assume the front of your robot is the top of the H and the center wheels are for side to side movement. -Hypothetical 1 (Pushing robot in front of you) On paper the omnis should work perfectly fine for this head on movement. The second you introduce an angle your wheels are losing efficiency. If you put this drivetrain against another head on, you'll lose the fight. That center plaction wheel won't help either, it will act as a brake if you put it down. -Hypothetical 2 (pushing a robot on your side) Let's put that plaction wheel to the test! A robot is driving past you and you're facing it head on. It gets on your side, you push it three feet off its path and it goes on its merry way. -Hypothetical 3 (Front of opposing robot on your side) That last one was a bit pessimistic, lets a assume your side is facing them. Thats where the pushing power is! You get in their way, put down that plaction wheel getting ready to push and they strafe around to the front of your bot. You're stuck there because you cant move against that plaction wheel. By the time you lift it to try again its already too late. -Hypothetical 4 (Front of opposing robot contacting your side AND you get your wheel down quickly AND they don't strafe) Ok ok, now for the ideal one. You have your side to an opponent, you make contact and throw down your wheel microseconds away from pushing. Let's assume your opponent doesn't try to strafe so its a straight pushing match. Now stop and think, is your one plaction wheel powered by two cim motors going to win this? Is it going to make a dent (in efficiency not literally)? That other robot could be running twice as much power, three times at much! When was the last time you saw a drive system powered by only two cims? Even if that's what you were dealing with they will be using more wheels giving them more traction and more pushing power. -Results Your design is based off of that plaction wheel giving you extra traction, but it slows down a design that ultimately hinges upon speed and agility. Even if you get into pushing someone it wont be much power at all. Strong robots can afford to be slow and clunky because its tough to stop them, an H drive NEEDS to be fast and agile. If you actually built one of these drivetrains for competitions, your drivers would stop using the plaction wheel and just switch to using the omni because the plaction wheel hinders you more than it helps.
Its obvious you put a lot of effort into this design, and I'm betting youre a better designer for it. Just remember that not everything you make needs to completely reinvent the wheel so to speak. A KOP H drive would be awesome, and you're awesome for coming up with it! I say ditch the plaction, put a faster gearbox in the middle, and take some time to really think "should the straif wheel be fixed or retractable like it is now?" Then publish the files, tell everyone how to make one and design on you crazy diamond!
I think using the traction wheel as a brake would be the most useful application of this, to stop people from pushing you.
Here is a link to our spin on the classic H/I drive from last year.
We call it the Flying Hawaiian Drive. Some referred to it as the Klingon Bird of Prey.
Sorry the pneumatic cylinder is not in this picture. It goes between the two tabs between the wheel legs.
Your design, which was built and videoed by a few teams so far, and are posted on YouTube, is solid, but has only one driving wheel for strafing at any time.
We did CAD and started to build prototypes of this type of strafe system last year.
Unfortunately this type of actuation puts the strafe wheel system too low and would not give enough ground clearance when traveling over the scoring platform last year.
This is what spawned our design, we wanted strafing but didn’t want to give up being able to drive over the scoring platform and wanted as much traction as possible with all that tote weight.
If you like I can send you the CAD files and / or post current pictures of the working assembly.
Looks good and a great CAD project to be refining those skills.
Keep it up!
I am not sure if what I am thinking is a very good approach but it would seem that by using a high-speed/low-torque gear ratio we would be able to somewhat get around this issue. The high speed would allow us to move quickly even though a percentage of our speed would be lost to slippage while at the same time our reduced traction would allow us to use less torque without a stall. How does the gear ratio of approximately 4:1 for the plaction wheel and 2.81:1 for the omni wheel sound using for using with 3 CIMs? If these are ridiculously low (I am pretty sure they are) we could do something more on the level of 5.95:1 for the plaction and 4:1 for the Omni.
I guess I agree with you here. I was referring to it as ‘I’ Drive to demonstrate the difference between a normal H drive where the four omnis at the corners doing the primary driving and this design when it would use the center omni/plaction for general movement. I am not sure I this makes sense but this drivetrain could be thought of a “long-Idrive” rather than a “wide-Hdrive”.
Uh oh, this is where your misunderstanding starts showing. The front of this robot should be thought of as the top of the ‘I’ (or the side of the ‘H’) and the center wheels are for forward backward movement while the omnis at the corners are for strafing/turning.
Thanks for all the critical feedback. Believe me, I really appreciate it even though I might sometimes not completely agree on you!
No matter what, a H drive (or any omni-directional drive besides swerve) is not gonna do so great at defense. I was mostly thinking that for this design the plaction would act more as a drop-down drive-able brake that would prevent someone from pushing you halfway across the field sideways on your slippery omnis. The drivers would spend most of the match on the 5 omnis but would only resort to the plaction to stop your opponents momentum as the bulldoze you or to play some (very) light defense.
The design would still have good highspeed/maneuverability. The picture was unclear, there are 3 CIMs driving the toughbox and the omni and plaction are geared up.
Although the design is far from perfect (I would never use it as it is for a actual competition robot) it will hopefully inspire something that we can realistically use for build season. I have to keep everything to stuff that is already in our stock or is readily accessible to buy. Although it is not perfect it would provide my team with: fully omni-directional movement, shifting (omni is shifted up 1.5x over the plaction), ability to avoid somewhat some omni drive problems (more pushing ability, braking).
Even if you had 6 CIMs geared down 50:1, you still couldn’t generate more pushing force than the strafe wheel’s coefficient of friction times the weight loaded on that wheel. It’s pretty hard to see how you could get much more than half the weight on that wheel under good conditions, and you’d probably be limited to a third or less if you got into a pushing match. You would never be able to keep up with a decently designed robot with four or six of those same wheels (which collectively bear all of the robot weight) all pointing the same direction. Also, because you only have one traction wheel, there are minimal forces available to keep you from being spun by an opponent.