pic: Prototype Drivetrain v2

[EricH]

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

[548swimmer]

Originally Posted by EricH

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?

[Edoc'sil]

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

http://www.flickr.com/photos/47595136@N03/4592232432/
http://www.flickr.com/photos/47595136@N03/4591612471/
http://www.flickr.com/photos/47595136@N03/4591612485/

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

[548swimmer]

Originally Posted by Edoc'sil

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

http://www.flickr.com/photos/47595136@N03/4592232432/
http://www.flickr.com/photos/47595136@N03/4591612471/
http://www.flickr.com/photos/47595136@N03/4591612485/

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.

[Edoc'sil]

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.

[548swimmer]

Originally Posted by Edoc'sil

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.

Yeah, they might be okay with a closed system, but I know they don't like adding compressors. That's why I'm currently using springs.

Any ideas on how I could tension the chains in the current configuration?

[Edoc'sil]

It seems foolish to throw away a useful tool.


And simply no, I do not see a good way to tension it like you have it set up now, mainly do to the fact that springs in a tensioner will allow chains to slip.

Something like this could be converted into that tensioner from mcmaster mentioned earlier. I have never used this style to tension, I have no idea how they work. http://www.mcmaster.com/#sprockets/=70knoq


The link isnt working here is the pn 6793K19

[548swimmer]

Originally Posted by Edoc'sil

It seems foolish to throw away a useful tool.


And simply no, I do not see a good way to tension it like you have it set up now, mainly do to the fact that springs in a tensioner will allow chains to slip.

Something like this could be converted into that tensioner from mcmaster mentioned earlier. I have never used this style to tension, I have no idea how they work. http://www.mcmaster.com/#sprockets/=70knoq


The link isnt working here is the pn 6793K19

Wouldn't an active chain tensioning system work? So there would be two pieces of nylon with machined slits for the chain to pass through them. They could be hooked together with springs about 75% as strong as the springs on the suspension. As the suspension traveled, the springs on the tensioners would take up the slack generated by the travel. This might work better with an idler sprocket in between, but I'm not sure.

[LLogan]

Originally Posted by 548swimmer

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.

The bolded part does not entirely make sense for what you want to do. There is absolutely no point in keeping all the wheels exactly level if only the center ones are driven. Your rear wheels will not be driven, so it's quite useless to increase the normal force on them. In fact, it's detrimental because you're decreasing the normal force that is on the center wheels.

I am unsure of why you are so set on a suspension.

Originally Posted by Edoc'sil

Forget the suspension if you are not doing two things:

Driving over rough terrain like the bumps
Powering all wheels

The whole point of a suspension is to make sure that the normal force is distributed as evenly as possible. Doing this is only advantageous when each wheel is powered, seeing as your tractive force is based on the sum of the forces of friction and thus the normal forces.

My advice: a suspension is not worth the hassle (and relatively useless) unless you are powering all wheels, or going over a surface that is not flat. To compensate for the sudden stops and starts, perhaps you could try to scale the acceleration and turning to your discretion through programming.

[548swimmer]

Originally Posted by LLogan

The bolded part does not entirely make sense for what you want to do. There is absolutely no point in keeping all the wheels exactly level if only the center ones are driven. Your rear wheels will not be driven, so it's quite useless to increase the normal force on them. In fact, it's detrimental because you're decreasing the normal force that is on the center wheels.

I am unsure of why you are so set on a suspension.



The whole point of a suspension is to make sure that the normal force is distributed as evenly as possible. Doing this is only advantageous when each wheel is powered, seeing as your tractive force is based on the sum of the forces of friction and thus the normal forces.

My advice: a suspension is not worth the hassle (and relatively useless) unless you are powering all wheels, or going over a surface that is not flat. To compensate for the sudden stops and starts, perhaps you could try to scale the acceleration and turning to your discretion through programming.

I just found a way to drive the wheels, keep the suspension, and tension the chains all at once . I'm currently rendering it, and will post it once it's done. This is just in case we don't have a flat surface next year. If we do, it'll most likely get nixed.

[kgzak]

I personally like the suspension even if we have a flat surface. Last year the field was flat but at nationals we kept having issues with one or two wheels not touching the ground because of our pick up mechanism which had to touch the ground. There were bumps in the actual field which caused our pickup to touch the ground but our front two wheels did not. I am designing a suspension so this does not happen to us agian. We were using 4 Wheel Drive which is different but the idea is still the same. My design will be for mecanum.

[548swimmer]

Originally Posted by kgzak

I personally like the suspension even if we have a flat surface. Last year the field was flat but at nationals we kept having issues with one or two wheels not touching the ground because of our pick up mechanism which had to touch the ground. There were bumps in the actual field which caused our pickup to touch the ground but our front two wheels did not. I am designing a suspension so this does not happen to us agian. We were using 4 Wheel Drive which is different but the idea is still the same. My design will be for mecanum.

I'm not sure if you're interested, but what I did to solve the solution may be applicable to you guys too. Feel free to be inspired by it.

[kgzak]

Originally Posted by 548swimmer

I'm not sure if you're interested, but what I did to solve the solution may be applicable to you guys too. Feel free to be inspired by it.

Well I was going to have the motor move on the suspension as well but your idea might be better.

[548swimmer]

Originally Posted by kgzak

Well I was going to have the motor move on the suspension as well but your idea might be better.

I'm not sure with mecanums, cause you need one motor/wheel, and mine is designed for all of the wheels on one side to spin the same way.

[kgzak]

Originally Posted by 548swimmer

I'm not sure with mecanums, cause you need one motor/wheel, and mine is designed for all of the wheels on one side to spin the same way.

Yes but I could use the same concept. I would like to keep the motors stationary and that would make the suspension be able to be lighter.