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pic: 6 wheel drive with a suspension
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Re: pic: 6 wheel drive with a suspension
I might be totally wrong here, but i think there is a huge problem with this design.
The chains going to the omni wheels in the center should not be there. Imagine what happens if two mechanums on the same are rotating in different directions in order to create a strafe movement, what happens is that the sprocket on the center omni wheel is getting pulled by one chain forwards, and by the other one backwards, thus, assuming the powers are equal it will not rotate at all, and the mechanums will not rotate either, and therefore you will never be able to strafe. If i am correct, you have to consider removing those chains, and leaving the center omni wheel unpowered, or powered by a different motor. Can someone more experienced tell me if i am correct here? |
Re: pic: 6 wheel drive with a suspension
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Re: pic: 6 wheel drive with a suspension
Very logical assumption and good observation! however, in a previous thread discussing the same design, it was revealed that the chains tie into a ball differential for the center Omniwheel... this way if the robot is going forwards or back, the chains are going in the same direction, and the Omniwheel will roll. If they are strafing, then the chains will be going in opposite directions, canceling each other out, so the sprockets will free-spin and the Omniwheel will not turn. If it is going at an angle, the Omniwheel will move slightly back or front.
While I am having a little trouble understanding how the ball differential physically looks, I LOVE this idea! Well done! |
Re: pic: 6 wheel drive with a suspension
In a top view, you want the axis of the rollers on each wheel to form an X so that the rollers form an O or a diamon on a bottom view.
If this were a bottom view, it would be fine. If this is the top view, all you need to do is swap each wheel with it's counter-part. |
Re: pic: 6 wheel drive with a suspension
Still don't see why the Mecanums can't be directly driven from the banebots shaft, rather than through Helical gears, but looks like a very interesting concept. Please keep us updated on any prototyping efforts.
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Re: pic: 6 wheel drive with a suspension
The reason we do not drive the wheels straight off the Bainbot shaft is to allow for straight driving. You know that the motors drive faster one direction than the other direction. Using them on helical gears the way we are make the motors go the same direction when the robot is going forward thus the motors are running at the same speed. So when we program for autonomous we will not have any problems with it pulling to the right or left.. Also note that when the robot goes sideways one set of motors will reverse so they will be going the same direction again allowing for straight travel.
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Re: pic: 6 wheel drive with a suspension
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We had a robot a few years ago that would unexpectedly turn slightly under autonomous control. Calibrating the Victors to the RC output fixed the problem completely. We've made it a point to calibrate them ever since, even including a special function in the robot code to sweep a selected PWM output from full forward to full reverse and back to neutral. (Last year, we defined full forward as 228 and full reverse as 28, and we did a similar calibration for our joysticks. It made working with the code a tiny bit easier to have the valid range of both control and output values be +/- 100.) |
Re: pic: 6 wheel drive with a suspension
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Re: pic: 6 wheel drive with a suspension
okay, so ive been trying to understand how ball differentials work, and i think i have the basic idea down. they have the same function as a normal differential, but can be more compact. i rendered this to help myself understand how it works. i was trying to get it animated, to show the different directions, but the constraints just werent working.
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Re: pic: 6 wheel drive with a suspension
we used a drive train like that in class once
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Re: pic: 6 wheel drive with a suspension
I assume that with mecanum drive you will be using encoders on all wheels. If so, you can fix any lingering bias issues in programing, using feedback from the encoders.
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Re: pic: 6 wheel drive with a suspension
One thing to note here. If your pivoting the "modules" about the steel tubes (that's my assumption) then whenever your suspension moves the distance between the steel tubes is going to change. Seem like it could be hard to mount other robot pieces on a dive base that keeps changing size.
I can see why you might use the helical gears just to save space in the chassis but it would seem like the price wouldn't justify the cost. Although if you had some of the old helical gears from 2004 and previous season lying around I would definitively see the benefit. |
Re: pic: 6 wheel drive with a suspension
Pasting from the other thread:
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You should be able to account for this in code by adding a small backspin to the front mecanum wheel, yet there may be a bit of tweaking to make it smooth from zero to 90 degrees in each quadrant. Good luck and keep us posted! |
Re: pic: 6 wheel drive with a suspension
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