CAD is finally completed! We are aware that then mecanum wheels are backwards but did not want to redraw. The frame of the robot will be supported on the steel rods. The omni wheels have a ball differential between the sprockets to allow them to stall during sideways maneuvers and to drive going forward or reverse. The drives will pivot on the support rods and at the omni wheels with a slot on one drive to allow the suspension to work. We can install springs in the suspension if it needs to be stiffer.
if your only using two rods it seems that it would not be strong enough and it will be pretty loose you may have a problem with the frame bottoming out
Can mecanum wheels be backwards as long as the diagonal wheels are in sync?
Yes… but there are some ramifications to that, like it’s now easier to spin you around. You may also need to reverse some code for going sideways.
so what the difference between:
/ … \ /
\ /and /
which is right?
hmm, looking at this again and the left one would tend to turn when the right one wouldn’t? Interesting, I never thought of that until I looked at them side by side.
Typically, the “O” pattern is used. The “X” pattern may also be used. (When seen from the bottom; top is the opposite.)
I am not sure exactly what you are saying far as bottoming out. When we build the robot base it would be secured the length of the rods which are tubes. The base will most likely cover the whole empty area between the drives. We are using tubes (which we may increase the size) so we can slide the bumper bolts into the tubes and than slide pins into them to hold.
http://www.team1322.org/ideas.htm for a side view of the suspension.
Rather than increase the size of the tubes, you could also rivet lightweight honeycombed fiberglass or 1/16" sheet aluminum to the bottom, or 6" strips of either. It will greatly increase the rigidity of the two frame segments while also leaving the flex you want for suspension should the tubes not be enough.
This control system is straight up intriguing. The matlab plots are all obscured when the normal unit vector controls are put on it, though I may have the omni wheel’s equation incorrect. I hope this succeeds; it will be as fascinating as ‘twitch’ drive to figure out.
I’m wondering about how the rest of the robot is going to fit on this frame. As the front arm moves up, won’t it force the rest up (and back) as well? I’d be afraid of the CoG with a frame like this. If the center was kept very low, I could see this working.
Along with the previous comment, regarding upperstructures and other things that mount to this, what’s going to happen with electronics? Having a flexing board seems like an electronic person’s nightmare.:yikes:
More reasons for it to be an electrical problem than a mechanical or programmers.
What happens to the rod when the front left wheel wants to go up and the front right wheel wants to go down?
bottoming out refers to the frame hitting the ground
unless you have enough ground clearance when you accelerate wouldent you frame be so (snakish)? that it would move with every little bump or change in velocity i dont see how you could attach an upper structure to it
The manipulator mount problem is easy in concept to solve, but it adds weight. The main base of the manipulator would have to be fully supported by one of the frame segments (forward or rear) and the angled supports that attach to the opposite frame segment would have to be broken up into two parts that attached to a gas shock or compression spring in a “Y” formation. So rather than seeing one solid bar for the angle support, we would see a “Y” with the compression spring/shock forming the base of the Y. Note, not a “T” formation because a “T” wouldn’t allow the frame to flex up and down.
CoG and stability would have to be tweaked, but it is definitely possible.
The rods are pivot points only and do not move or flex. A base of the main part of the robot will be attached to the rods. The rods are only showed to tie the two halves together. The rods only need to be long enough to go from the base through the drive units to allow for the pivot. When built we would limit the amount of pivot needed for any ramps required. We could also connect pneumatics to lock down the suspension for any long reaching manipulator. View http://www.chiefdelphi.com/media/photos/31755 to get a better understanding of how the base would attach to the rods. One half of the drive unit has slots to alow for the movement of the suspension. If you look close at the drowing you can see the slot and hole.
Perhaps I am misunderstanding the CAD model – but how is it that the rods act as pivot points? My understanding was that each side pivoted about the omniwheel’s axle. Your team’s website corroborates that understanding.
Allowing one rod to slide in the mecanum wheel module serves to limit the travel of the suspension – and any base mounted to would require similarly slotted mounting to remain in place.
This arrangement, however, does not allow for implementation of an independent suspension, as you’d mentioned in other threads, and is the source of my confusion.
If you were to approach a ramp at an angle, one mecanum wheel module would begin to climb and the opposite side, because it’s connected by the steel rod, would follow suit – losing contact with the ground. The vector addition that allows a mecanum drive to travel in a straight line is then lost and you will lose control of the machine.
I will try to explain. View the picture at http://www.chiefdelphi.com/media/photos/31755 The base of the robot which will include any arm device and all other components will have the rest of the robot weight, will have two rods extending out of each side of the robot. One set of drives will slide over these two rods and be pined in place to allow for the pivot motion. One of the rods will slide into a hole of one drive and the other rod will slide into a slot (to allow for the small amount of back and fourth movement). If you lift one of the mecanum wheels that portion of the drive will pivot pushing down on the omni wheels (lifting the robot) and then the other portion of the drive will pivot and slide on the other rod (that is attached to the main part of the robot) and lift the other mecanum wheel. This action should be independent of the drives on the other side. This is very similar to the pathfinder robot on mars but not as elaborate. The amount of travel will only be the amount needed for the largest ramp. Movement can be controlled by a pneumatic connected at each omni and to the frame.
When a pair of mecanum wheels drive toward one another, won’t they first force the rod toward the other end of the slot, forcing one or both ends into the air and losing traction?
I’m trying to wrap my head around this. I still do not understand how a solid rod – or a base that effectively acts as a solid rod – can allow for, say, the front left wheel to go up a ramp while the front right remains level. The slotted end can handle this condition, but the fixed end cannot, as far as I can tell – at least without expecting that the omniwheel can shift both upward and downward. In that case, I don’t understand how you reasonably expect to know which direction the omniwheel will tend to shift.
No, the piviot at the omni will not allow theme to come together. Technicaly if the robot was very light and there was enough force from the drives you could lift the omni when the mecanum drive toward each other.
I placed a drawing on our news page to help with a visual. http://www.team1322.org/news.htm