Thanks everyone for the input on the first one. I did this one based on suggestions made by others and few ideas of my own. To give a base frame of reference this idea was for an all terrain swerve that would be driven near my home. The terrain would be rough but mostly just dry grass and dirt, perhaps mud but not a lot (fairly arid climate). Driving will be done in a very open area and almost all turning would be done while moving.
The changes that were made:
- Wider treads to give a smaller PSI when driving in loose dirt and gravel. At about 70 pounds including controller and battery it would be about .875 PSI. The wider treads also had the effect of pulling the CIM in so that it doesn’t stick out as far and is in less danger of damage.
- The gears are now protected from dirt and water by a shield made from several layers of routed polycarb (same stuff that makes the rest of the gear box). This would be to protect during dusty conditions and muddy driving.
- I changed the frame because the former would always have one module off the ground unless on a perfectly flat surface. While on a FIRST field this is no problem, on a dirt bike course this could cause instability.
I have done the math to see how much torque it would require for that motor to turn the modules. Given a coefficient of friction of 2 (much higher than it would be on loose dirt or gravel) and that the weight is concentrated at the corners of the treads (absolute worse case scenario, also means that I don’t need to do an integral) based on this I know that it would require 10.208 foot pounds of torque to turn the module. A fisher price run through a banebots 256:1 gear box that is sticky (~50% efficiency) has ~40 foot pounds of torque giving it more than enough torque to turn the module.
Thanks again.
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:yikes: I get positively giddy when people show us the numbers.
It helps all of us to see the assumptions that others are using, and the types of calcs being done. Nice explaination of the changes too.
Assuming the that frame articulates in the center, what made you go with that type of suspension vs. a horizontal pivot perpendicular to that? (eg. the front axles both move up at the same time) Runs off to look for picture
Mark
wow…
I love your design here and the treaded crab modules look very clean and well desinged. I am very curious to what your purpose is and what is going on top of this fantastic base.
This one is a big improvement…congrats
Your design is interesting, but I would recommend that you do some more analysis on it for the next version.
I am concerned about how the frame would handle an impact on the side of either the front or rear (the two rectangular sections). It seems that (unless you have an extrememly beefy frame in the middle bar) that there would be some bending or buckling. From the impact there would be a large moment acting on the rectangular part of the frame, and since the two sides are not joined, there is not much supporting it.
Keep up the good work and the idea is great!
First off, amazing! I wish i were better at CAD! I hope to learn someday how to build my ideas, turning them into something that others can see more readily.
Can we get some size specs? how long is each tread section? Where are you going to obtain said tread? What sort of material is the superstructure?
Thanks in advance i hope…
That’s really cool!
How does the middle bar work? In what way is it connected?
Nice design… but watch your assumptions on the FP/Banebots combo. I get the sense (now I’m the one making assumptions) that you are using the peak torque figure for the FP when calculating your output. FP’s don’t last long at peak torque. Since this motor will be in intermittent operation and you have calculated a factor of four over your peak design load, you will probably be okay, but I normally calculate FP torque based on a 10 amp load… and even then plan to provide cooling for continuous operation.
Secondly the little BB 256:1 gearboxes have the ability to pull themselves apart when driven to the peak torque of an FP. I highly doubt that 10 ftlbs would be a problem, but 40 is starting to get up there.
So assuming your load calculations are correct, your design should still work, but I don’t think you have nearly as much “extra” torque to work with as you have calculated.
Here’s a suggestion that came to mind the first time I saw this design… why not also pivot the tread modules about one of the rollers. That way you could also lift the robot up onto “tiptoe” when more ground clearance is needed. No reason it couldn’t be done with pneumatics if you didn’t want to slip another motor down there.
Jason
