pic: 3 wheel omni drive concept

[GUI]

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

[s_forbes]

Originally Posted by GUI

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

Ooh, check out Mr. Spoily McSpoilerpants over here.

[dirtbikerxz]

Originally Posted by GUI

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

CAAAAAD

[Aren_Hill]

Originally Posted by s_forbes

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!

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

-Aren

[GeeTwo]

Originally Posted by z_beeblebrox

... how damage is avoided when the robot tips over (that's a lot of energy that has to be dissipated).

Originally Posted by s_forbes

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).

[image]

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.

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

Originally Posted by s_forbes

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 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.

[dtengineering]

Originally Posted by Ari423

I wasn't saying that wood robots won't work. ... you could see legal wood on metal contact ... and that scares me.

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

[efoote868]

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

[s_forbes]

Originally Posted by GeeTwo

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 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!

[Ari423]

Originally Posted by s_forbes

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!

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).

[GeeTwo]

Originally Posted by Ari423

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).

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.)

[Ari423]

Originally Posted by GeeTwo

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.

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.

Originally Posted by GeeTwo

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.)

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.

[s_forbes]

Originally Posted by Ari423

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).

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.

[Chris is me]

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.

[GeeTwo]

Originally Posted by Ari423

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.

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

Originally Posted by Ari423

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.

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.

[hrench]

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.