pic: Prototype Drivetrain v2



Weight ~ 30lbs
The omnis ARE NOT driven, if anyone has any idea’s on whether or not the suspension is worthwhile or how to drive with suspension, please let me know.

I would recommend powering all of the wheels that will be in contact with the ground, including the Omni wheels. In addition to that, are you planning on using the custom traction wheels shown in this model? If so, do the spokes require 3D contouring?

I’m not sure how to power the omni’s when they’re in a suspension. We may use the custom wheels, the spokes are flat, no fillet’s into the rim.

What, may I ask, is the point of the suspension?

could you possibly design a suspension that could keep a chain tensioned? Possible have it move around a point that would have the chain stay tensioned as it goes up and down?

Or could you have a chain tensioner that keeps a chain tensioned by use of springs and have the springs that hold the chain tensioned be easier to compress/expand than the spring or whatever you are using to make the wheels have suspension.

I am trying to design a suspension for our robot next year but the wheels would be powered in one way or another I don’t see a point in having a suspension if you are not going to power the wheels. What is the reason behind having a suspension on unpowered wheels?

Why exactly do you need suspension?
Wouldn’t it be much easier to lower the center wheels by about 1/8" and power the other wheels with chain? or just going flat 6WD?

The suspension is there to improve handling, much like a rocker, only smoother.

I was thinking about widening the carriage for the suspension and putting a dual sprocket with a bearing on the dead axle that is the pivot point. Then run chain to the omni.

The point of using omnis is to avoid needing to “rock.” I don’t get how it would be smoother to have it rock AND have omnis.

And if you want it to rock, why don’t you just drop the center and forget about the suspension?

If you want to still have the suspension, you could either do what you suggested or make the suspension go up and down along an arc with radius equal to the distance between the front and middle wheels, so the chain has a constant distance.

Have you encountered a deficiency in the handling of a rigid (non suspended) drive?

How can I make the carriages pivot around the center axel?

There is currently no rock at rest. Once you begin moving the suspension absorbs any jarring movements like sudden stops or turns, making it handle more smoothly.

As sanddrag said, have you had any problems with a rigid drive? How much are you planning to have it rock? Too little rock and it would be practically the same as a rigid drive, and too much rock might affect accuracy of manipulating the game object due to uncontrollable front/back rocking.

Don’t get me wrong, I think your idea is really cool. It’s just the matter of seeing if all the effort to get it to work is worth it, and if the benefits are true benefits.

I don’t know if this would work structurally, but you could cut slots and make a block that rides in the slot.

The other option would to be have a long arm pivoting on the center axle, but that might be too heavy/bulky for practicality.

We haven’t had any issues with handling, but why not investagate this in the off season.

With springs tensioning the suspension, it will rock only as far as it needs to. Using a diff. eq. we can figure out the specs on the spring. Ideally, at rest, the spring keeps the wheels exactaly level. Once the robot starts moving and the CG “shifts” the springs will expand cushioning any sudden blow (like a rapid acceleration). Additionally, if this robot starts to get flipped, all wheels can stay on the ground providing some traction. The front ones would lift off the most, increasing the Fn on the rear and center

That still leaves the problem of chain runs though. I’m not sure a slot would have low enough friction, plus the exterior has to be smooth for the bumpers.

How about this: Run the chain so that it is long enough to handle the longest dimension, and stick a couple of McMaster part 5896K1 in there as tensioners. That should help keep the chain tensioned correctly, if you don’t have too big of difference between longest and shortest chain runs.

We use 25 chain though, so that won’t work. I guess we could always make our own…

Do you have any experience with whether or not these fall out or how they work? I don’t see how they could tension in a situation like this.

Not these–they go in the chain, and don’t contact the robot frame at all. Should be negligible effect on the suspension.

Yeah, I realized that after I posted. How would these work in this situation? If they tension, how do you get them in? Do they allow for the variable chain lengths?

Forget the suspension if you are not doing two things:

      Driving over rough terrain like the bumps
      Powering all wheels

You speak of a “smother ride” and I really do not understand what it will benifit you. If you are concerned about your electronics mount them on a foam surface, or some other kind of protection. If you don’t want to jostle the rest of your bot, well, almost all of the jostling comes from collisions, not deceleration from turning and stopping.

Also if your bot cam into any kind of pushing match it would distinctly be in the featherweight class. Not only will the omnis make it so that you well be easily spun, the 4 useless wheels will give you significantly pushing power. On your v1 thread you mentioned that you mechanical guy said he could put 75% of the weight in the center. I do not see how that is possible when you don’t know what next years challenge is.

Here is one way to keep the chains in tensioned



Power the middle wheel run chain to the other axles, and then add a suspension to the angled bars with closed pneumatics.

I do want to power the omni’s I’m just not sure of the best way to go about this. I like your idea of running pneumatics as shock’s, but many members of my team have something against them, so it will be a battle to get them incorporated. I was hoping it would be possible to use springs for the suspension because they add less complexity and weight.

As for the weight distribution, that 75% was assuming the CG was in fact in the geometric center of the robot, and it usually is pretty close to that.

This whole concept may never get built. This is just to inspire the younger designers that I’m training over the summer and to provide us with a jumping off point for next year’s challenge. If there is a surface feature like a large washboard or uneven, low steps going up to some important game piece, the suspension will be useful.

Your team doesn’t like pneumatics? That makes life harder. The same idea works with springs, they just may wear out and cannot be adjusted.