27-11-2016 23:17

asid61

Re: pic: 3 wheel omni drive concept

Your avatar seems very suited to this kind of drive.







In all seriousness though, what exactly am I looking at here?

27-11-2016 23:25

AdamHeard

Re: pic: 3 wheel omni drive concept

Love the kickstands.

27-11-2016 23:45

s_forbes

Re: pic: 3 wheel omni drive concept

First make a segway robot. Then add a third wheel so it can go sideways. Your robot's profile is now 1 foot wide when it sprints down the field.

The self righting mechanism is probably more entertaining, but the kickstands are an absolute necessity to start a match. Building them this way lets you lock them in a slightly over center configuration when deployed, so the robot won't tip even without air.

28-11-2016 00:05

pwnageNick

Re: pic: 3 wheel omni drive concept

If this ever makes the competition field, I will personally buy you your own personal Segway.

28-11-2016 01:24

cadandcookies

Re: pic: 3 wheel omni drive concept

He'll call you on this in 2025 or something when things have changed so much that this is viable.

28-11-2016 02:05

Chak

Re: pic: 3 wheel omni drive concept

What's the piston on the side pushing the strange half-gears doing? I can see it pushing the two little wooden paddle things, but those don't seem to be attached to anything.

28-11-2016 02:17

DanielPlotas

Re: pic: 3 wheel omni drive concept

Kickstands so it won't fall over pre-match.

28-11-2016 06:49

Sperkowsky

Re: pic: 3 wheel omni drive concept

Can you make a gif of the kickstand and gear motion. I am having a hard visualizing the motion.

28-11-2016 07:42

carpedav000

Re: pic: 3 wheel omni drive concept

Is the self-righting mechanism pictured?

28-11-2016 07:48

GeeTwo

Re: pic: 3 wheel omni drive concept

Interesting!

Is the strafe (center) wheel actuated to provide a constant (or adjustable) force against the carpet? As the robot leans into "forward" acceleration, the strafe wheel will otherwise tend to rotate off the carpet.

What is the "peg" sticking out the side just to the left of the strafe wheel?

If hit hard enough on the long side, or if power fails for a moment, it will go down. If I were to do something like this, I would use a kickstand that could be used to pick the chassis up off the carpet afterwards. (sniped!)

With this extreme an aspect ratio, it is possible (under 2016 rules) to have a gap in the bumpers so wide that another robot can hit your robot square and hit nothing but frame perimeter. I would anticipate a change in bumper rules after the first year this concept hit the carpet.

28-11-2016 08:29

Kartoffee

Re: pic: 3 wheel omni drive concept

The rules state 8 inches from each corner. This is to stop metal-to-metal contact. If this robot "strafed" between another robot's bumpers, it would be metal-to-bumper contact.

Also, of course, nobody who is aspiring to win much more than Innovation in Controls will make this, so I don't think the GDC needs to panic yet.

28-11-2016 08:45

Ari423

Re: pic: 3 wheel omni drive concept

Judging by the appearances and the finger joints, it looks like a majority of the frame is made out of wood. I would be a little sceptical of bumpers hitting wood repeatedly in high-speed collisions.

28-11-2016 09:44

Chris is me

Re: pic: 3 wheel omni drive concept

Other than the clearly ridiculous nature of this robot, the main thing I see being a real hiccup with it is the shape of the center omniwheel. Since it isn't really round in profile, I don't think the robot will tip forward or backward on the wheel smoothly. It'll take weight off of the left and right wheels when the robot tips at certain angles and put more weight on them when tipped at other angles, and it may prevent the robot from righting fully at certain points. I'm not sure I'm describing this well, might need to draw something.

I think this could be fixed either with an active suspension, or in a far more boring way by making that third wheel outboard of the other two, forming a sort of kiwi drive. But the latter would destroy the whole concept of the robot, so where's the fun in that.

This is far from the first wooden robot frame in FRC - teams have been doing laser cut wood frames for years. They can be done very robustly.

28-11-2016 10:26

s_forbes

Re: pic: 3 wheel omni drive concept

The middle wheel is sprung. The module pivots around the peg that you see and is forced into the ground with a spring (latex). This keeps it's downforce constant into the carpet. I had an idea for an adjustable force mechanism, so you could prioritize whether the center wheel or the outside wheels saw more load depending on which direction you were accelerating. It seemed a little farfetched though.

This is what the robot would look like with bumpers. The kickstand is needed because the self righting mechanism is really large and cannot be deployed at the start of the match.



And here's another look at the kickstand mechanism:



Wood is good! It's far and away my favorite material. With bumper rules in place, you don't have a lot of metal on wood contact. I wouldn't expect anyone to hit this type of robot very hard anyway, because there's a chance it would fall onto your robot if you get too rough.

28-11-2016 11:22

Attention

Re: pic: 3 wheel omni drive concept

Um... what about high centering??

28-11-2016 11:23

Ari423

Re: pic: 3 wheel omni drive concept

I wasn't saying that wood robots won't work. I've seen a few of them and they often work well. All I was saying was if there is a gap in the bumpers large enough for another robot to hit inside, you could see legal wood on metal contact (with a manipulator outside the hitting robot's frame perimeter) and that scares me.

As for not wanting to hit that robot because of the possibility of tipping it: if I were a ref and I saw a robot play defense on yours resulting in a tip, I would be hesitant to call that an intentional tip. When you build a robot like that, you should expect heavy defense and make very sure your anti-tipping mechanism work as well as the inherent anti-tipping properties of a normal robot. Teams should not penalized because they were defending against a robot that isn't well build to play the game (which includes defense).

28-11-2016 12:27

CalTran

Re: pic: 3 wheel omni drive concept

I think the tipping thing was moreso I don't want a robot to land on top of my own, rather than the tipping penalty thing.

28-11-2016 12:33

DanielPlotas

Re: pic: 3 wheel omni drive concept

Why not use larger omnis for the sides? You could get your CG below the axles and then you wouldn't need nearly as complex mechanisms or software.

28-11-2016 12:40

AdamHeard

Re: pic: 3 wheel omni drive concept

There isn't enough of a lever arm to a CG below the axles (even w/ 8" wheels) to keep the robot stable when accelerating.

It also just isn't nearly as cool.

28-11-2016 12:52

BumblingBuilder

Re: pic: 3 wheel omni drive concept

Can you post a picture of the CAD for the strafe wheel module?

28-11-2016 13:50

GeeTwo

Re: pic: 3 wheel omni drive concept

These look like they need a tweak - unless there's a real perspective issue, they'll stick about half an inch outside the frame perimeter at the start of the match (presuming a 1/2" hex shaft on those wheels).

Did you plan some sort of end caps (possibly semicircular) to serve as frame perimeter behind the bumpers on the short end?

28-11-2016 17:16

s_forbes

Re: pic: 3 wheel omni drive concept

Click for larger:


Lots of small details would need to be tweaked to make sure all of the rules are met. This is one of those ones I'd put on the list of "things to fix before bagging". It's usually a very long list.

There would need to be some added support structure to satisfy the bumper rules (at least, if the rules stay the same next year). It wouldn't actually make the frame any stronger; the plywood portion of the bumper could easily handle all of the load from an impact.... but rules are rules. Bumpers seem to be one of those things where the letter of the rule is more important than the intent.

28-11-2016 17:44

GeeTwo

Re: pic: 3 wheel omni drive concept

Understood. The point is, I can actually think of a few times when this might have been a decent robot strategy/architecture, making these real questions. I don't recall the 2012 (Rebound Rumble) rules all that well, but as I recall it was not a highly defensive game. If you could easily switch back and forth from a vertical to horizontal orientation, drive in both, have a ball pickup and dispenser of modest speed at the "top" end that filled a "stack" of four balls, then you could have done great pickup, goal scoring, bridge tipping, and (obviously) bridge balancing with multiple partners. (I'm not actually sure you would have needed the strafe wheel.) Pretty much the same robot (sized for a single larger ball) could have also done well at STRONGHOLD, flopping and driving over most of the defenses, including the cheval de frise if you could figure out how to navigate the bumper rules.

28-11-2016 18:53

z_beeblebrox

Re: pic: 3 wheel omni drive concept

Nice work; looks like it will score at least 301 points!

I'd love to see a little more about the self-righting works and how damage is avoided when the robot tips over (that's a lot of energy that has to be dissipated). How will this avoid problems with the rule about extending more than 15" beyond the frame perimeter?

A minor plywood suggestion: offset the screws in the tabs and slots so that one side of the nut is flush with the plate that it's pressed into. The change is insignificant structurally, but speeds up assembly, as a hammer can be used to install and align the nuts, rather than each having to be inserted and precisely centered with pliers.

28-11-2016 20:45

hectorcastillo

Re: pic: 3 wheel omni drive concept

But does it go under the low-bar?

28-11-2016 21:03

Ari423

Re: pic: 3 wheel omni drive concept

...

28-11-2016 21:29

Aren_Hill

Re: pic: 3 wheel omni drive concept

I think you'll find the directional performance of that strafe wheel will be quite aggressive in one direction, and lackluster in the other.

Having the pivot off to one side results in the wheel trying to "drive under" the pivot when going towards it, and it lifting itself up when driving away from it.

I've seen this effect mitigated via using a linear up/down motion, or the fancy strafe module 148 used in 2014 that used this action to it's benefit.

Actuating it is another option, but has it's own downsides.

-Aren

28-11-2016 21:32

Travis Hoffman

Re: pic: 3 wheel omni drive concept

The battery will be mounted at the top, correct? There can be no other way.

28-11-2016 22:52

s_forbes

Re: pic: 3 wheel omni drive concept

Self righting would be done using a versaplanetary winding a strap to move an arm, one on each side of the robot. The arm would return to it's original position when the strap is let back out, using the magic of springs (more latex).



A damper to lessen the shock when falling over is a really good idea. I'm not sure where the best place to source parts for something like that would be. Some mountain bike spring/damper sets could be used, since they are lightweight by design. Maybe a simple low force gas strut could work, too.

The offset bolt position is a neat idea. You could probably accomplish something similar using centered bolt positions but putting a spacer under the plywood when you hammer in the nuts in.

That's a really good point. Using the toggling style of strafing mechanism is probably a much better application for this, since when it's not in use it leaves the full weight of the robot on the two outside wheels. (I believe this was first used on 148's 2014 robot?) You could probably spend a lot of time playing with the geometry to get it to work just right for a strafing segway robot, since the downforce is dependent on the geometry and how much torque the motor is applying. Would be a fun project!

I make a point to ensure that the battery is always impossible to get to. It might be at the top of the robot, but you will need to unbolt a mechanism to change it.

28-11-2016 23:32

GUI

Re: pic: 3 wheel omni drive concept

*cough* Why are you only posting screenshots? *cough*

28-11-2016 23:45

s_forbes

Re: pic: 3 wheel omni drive concept

Ooh, check out Mr. Spoily McSpoilerpants over here.

28-11-2016 23:47

dirtbikerxz

Re: pic: 3 wheel omni drive concept

CAAAAAD

29-11-2016 00:45

Aren_Hill

Re: pic: 3 wheel omni drive concept

Yeah, 148's bot in 2014 was the first instance of it, a JVN special (the VEXiq prototype was adorable).

-Aren

29-11-2016 07:29

GeeTwo

Re: pic: 3 wheel omni drive concept

You may also be able to achieve this by partially deploying the self-righting mechanism, and taking up the shock through backdriving the VP.

I did a white paper on the math of this sort of module about two years ago that may give you a good start. Note that this configuration will take more weight off of the wheel you're strafing away from than the one you're strafing towards; it may be easier to keep the balance routines working with a centered, linearly sprung/actuated strafe module.

29-11-2016 16:07

dtengineering

Re: pic: 3 wheel omni drive concept

Not wanting to detract from the main point of the thread, because I think the idea is pretty cool and I'd love to see a machine like this play the game on year, but designing with wood actually gives you the ability to create stronger, stiffer manipulators in many cases. The lower density results in a greater specific stiffness, particularly when dealing with solid cross sections.

I know you didn't mean to insult wood... I can see you've planned to use it extensively, but we do have a small but noisy "wood is good" cheering squad here on CD. I've built a few wooden robots and arms where the wood on metal contact wouldn't be scary for the wood structure!

Anyway, cool design. Look forward to seeing it go one day!

Jason

29-11-2016 16:07

efoote868

Re: pic: 3 wheel omni drive concept

I always love the discussions these ideas can generate.

This might have done well in 2007, I remember 1501 building a 2 wheel robot that year. Add a few ramps and you've got a nice robot

29-11-2016 19:48

s_forbes

Re: pic: 3 wheel omni drive concept

I like the idea of using the self-righting mechanisms as the brake for falling, it gives them multiple functions. I don't think the versaplanetary would like being slammed over and over again though. It probably would need a damping method between the end of the arm and the gearbox, or we would have to invest globs of money into spare versaplanetary stages.

I thought about several ways to implement this, and I think this is one of the better ways. Using a rear mountain bike shock on an additional joint on the self righting arm gives it damping ability, and is pretty adjustable. It looks like some air shocks have the ability to adjust the spring force (by varying the air pressure) and the damping coefficient, so it could likely be optimized to get rid of all of the bouncing after falling over. Pretty nifty!

29-11-2016 19:58

Ari423

Re: pic: 3 wheel omni drive concept

Is the plan to have the self-righting mechanisms only attached to the chassis through a single cantilevered shaft or is there something else not yet modeled? Because if so, that's a lot of force going through a cantilevered shaft, especially one only attached to a single piece of wood (again, not bashing wood; I would be sceptical with it only going through a single piece of sheet metal too).

29-11-2016 20:05

GeeTwo

Re: pic: 3 wheel omni drive concept

Taking the issues in reverse order:

Looking at the pics closely (particularly the one in post 15 of this thread), it appears that the shaft mounts through the tubing, not just the plywood.

These could easily become "U" shafts, with the other arm pivoted on the inside of the opposite "upright". If I'm picturing this correctly, each would not interfere with the action of the other. This setup would also support some idle rollers if desired to do things like the low bar in 2016 (Of course, the main drive train would need to be modified to make contact with the carpet when somewhat on its side.)

29-11-2016 20:31

Ari423

Re: pic: 3 wheel omni drive concept

I agree that in the pic in post 15 it looks to be going through the tube, but in the latest image on the far side there is a hole in the plywood not through the tube. On the other side of the hole there is something metal with a round bore in it, which I assumed was the bearing for the self-righting arm. I could be wrong, but that would mean that the hole for the self-righting arm either isn't modeled in the far tube or isn't at the same height as the one on the near side. I'll wait for some clarification from s_forbes for a final answer.

What exactly do you mean by "U shafts"? I'm not sure what you are referring to and I am having a hard time picturing how anything U shaped (or not U shaped for that matter) could connect to both arms without having to cross through the center of the robot, which I am assuming was intentionally left open to leave room for a manipulator otherwise there is no room to mount one. Also, I'm not exactly sure what problem you are trying to solve, because I only (intentionally) raised one point in that last post.

29-11-2016 20:31

s_forbes

Re: pic: 3 wheel omni drive concept

It is still mostly conceptual, so some things are missing from the model, and very few things are close to a finalized version. I think a cantilevered shaft that is attached to multiple layers of the main frame or through one of the vertical tubes would work best. But ideas change all the time as the concept progresses.

Good example: looking at the image I just posted, it occurs to me that bronze bushing would be much more suited for this mechanism than ball bearings.

29-11-2016 21:25

Chris is me

Re: pic: 3 wheel omni drive concept

Instead of using a solid 1/2" shaft and ball bearings for your arms, you can use a 7/8" OD .125 wall tube and bronze bushings. The bushings use the same OD bore as R8 ball bearings, and the tubing is the same weight as solid 1/2" round shaft, but the shaft is much, much, much stronger in resistance to bending, which is probably the main load to worry about here. This is one of my favorite COTS tricks for arm shafts.

30-11-2016 07:33

GeeTwo

Re: pic: 3 wheel omni drive concept

I took the new circle on the plywood as a bolt to help transfer torque from the plywood to the arm.




I was referring to an arm which mounted onto both uprights, not just one. It would only take up an inch on either side; the would still go across the robot either outside the frame perimeter or above the main robot chassis. This was also in response to your concern about a cantilevered shaft.

02-12-2016 10:09

hrench

Re: pic: 3 wheel omni drive concept

Do you intend to attempt to steer (make left and right turns) when its' in strafing mode?

I anticipate you could steer with a little input from the main two wheels, but I also think this would be really difficult to implement.

02-12-2016 10:35

MrForbes

Re: pic: 3 wheel omni drive concept

one of the most fun pics I've ever taken.

02-12-2016 10:45

Foster

Re: pic: 3 wheel omni drive concept

Would love to see the IQ version, any images of that around?