Hello Vex Forum,
So I was just browsing the threads on here and came across several posts about posting pictures of prototypes and open build seasons and what not. So I had the idea of creating a thread for the sole purpose of sharing some of your prototypes. I know GUS is always willing to put out some(but not all;]) of our information on the prototypes and tests we’ve done for this years competition to help better the competition and gain feedback on what we can do to improve. So feel free to post any pictures, videos, cads, ideas, little or big, anything that has to do with Gateway, High school and College. This thread is not intended to give away any big secrets, just little stuff you experiment with, stuff people should try, and stuff people shouldn’t even bother with. I will be posting stuff all through-out GUS’ build season, not everything, but stuff we feel fit to show.
Alright, for the first picture is a little CAD Andrew, from Aperture, helped me out with. It’s a 6 wheel drive, drop center, drive-train geared 3:5. The drop in the drop center will be obtained by a secret. I may post pictures depending of how the experiments go tomorrow.
Feel free to make any comments and questions! Thank you!
How did you decide to go with the 2.75in wheels as opposed to the 4in? Did it just work out better with the 3:5 ratio better? Also are those 393’s and if so are they at 100 or 160rpm? I’m guessing 4x 393’s at 100rpm.
At 4x 393’s at 100rpm:
With the 2.75" wheels you’ll be at 1.99ft/sec.
With the 4" wheels you’ll be at 2.90ft/sec.
The motors could definitely take the load of running at 3:5 with the 4" wheels even with a 15lb robot I’d say.
So any specific reasons for the 2.75?
Anyways I like the sprocket pattern. Especially in the middle; plenty of wrap on the middle wheel and very clean.
One thing I would be worried about is your outside C-Channel. It looks like they’re only held on with 2 stand-offs. You might want to add more to that; maybe some 1x2x1 C-Channel across connecting them since you couldn’t use the 1x5x1 C-Channel because it looks like they’re 3in apart.
I like how you’re able to keep the middle very open. I wanted the middle on mine to be as open as possible but with 6 motors I basically ended up building a gearbox for each side with 1x5x1 C -Channel in the back.
All in all great job so far. So how are you dropping the middle wheel? Taking a page from FRC and just precision cutting holes in the C-Channel 1/8" lower then the other wheels? That would be the easiest way to go about it.
Just to clarify; what you have on your drive is not planetary gearing. Simply motors mounted with their gears circling the gear, which would help prevent any skipping.
Epicyclic gearing (or planetary gearing) is much more complex/involved.
Thank you for all of the comments! I decided to go with the 2.75 in. wheels against the 4 inch wheels because I decided I could risk losing a little bit of speed in order the gain the tiny bit more torque, and I love tiny wheels;]. But then thinking about it some more I decided I was going to change the gear ratio up a bit because of the couple of experiments I did tonight at the robot meeting. I quickly figured out, the 60 tooth gears I was planning on using are actually a tiny tiny tiny bit smaller than the 2.75 inch wheels, so when you place it on the matting, the gears rub a little against the ground. I figured that wouldn’t be good, because it was causing friction, and everyone knows friction is bad in gearing and what-not. So I plan on finishing the drive-train Andrew and I CADDed, take some pictures, throw them on here to show everyone what was happening to hopefully prevent someone from making the same mistake I did.
As for the drop, I was debating on just shaving an 1/8th inch off of the diameter of the 2.75 inch wheels for all the outside wheels, or just doing what you said and drilling some more holes. Any more ideas?
My bad you’re absolutely right. Not in FRC mode right now.
I personally like the 2.75 in wheels better than the 4 in. The vexplorer wheels are larger by .1" in diameter lowering the center wheel .05". The chassis turns on a dime.
[FONT=Calibri]As you have recently found out, the 60T gear will drag and/or work against you when the robot is loaded down. Sounds like you are working toward an alternative to fix this.[/FONT]
[FONT=Calibri]I seldom like to build a robot chassis and drive train without the axles for the wheels being supported at two points. You will see some deflection in the robot chassis because of this unless you extend the axles between the 2 C channels. Right now the outer channels only serve as side bumpers protecting your wheels and motors and provide no structural benefit.[/FONT]
[FONT=Calibri]You may also want to look at the various combinations of motor sizes, internal motor gearing, wheel sizes, and possible geartrain combinations to determine the most efficient combination. The vex robot speed chart is a good start, but the particular one you provided a link to is a bit dated and does not take into account the H.S. chain & sprocket options or the new 393 motors. Consider finding an arrangement that utilizes less gears and chain/sprocket but still gets you close to the desired speed and torque.[/FONT]
[FONT=Calibri]Also consider utilizing the new 2.75” double Omni wheels as an option in your design in lieu of dropping the center two wheels.[/FONT]
[/FONT]
[FONT=Calibri]I seldom like to build a robot chassis and drive train without the axles for the wheels being supported at two points. You will see some deflection in the robot chassis because of this unless you extend the axles between the 2 C channels. Right now the outer channels only serve as side bumpers protecting your wheels and motors and provide no structural benefit.[/FONT]
[FONT=Calibri]You may also want to look at the various combinations of motor sizes, internal motor gearing, wheel sizes, and possible geartrain combinations to determine the most efficient combination. The vex robot speed chart is a good start, but the particular one you provided a link to is a bit dated and does not take into account the H.S. chain & sprocket options or the new 393 motors. Consider finding an arrangement that utilizes less gears and chain/sprocket but still gets you close to the desired speed and torque.[/FONT]
[FONT=Calibri]Also consider utilizing the new 2.75” double Omni wheels as an option in your design in lieu of dropping the center two wheels.[/FONT]
If I understand what you’re saying correctly, you think this is a west coast drive style with just outer protection. This CAD is not completely complete so it is missing the outer bearing blocks, and the axles. That’s my bad, >-<, Sorry! I am building this with two points of support. I have/am prototyping with what you said, a west coast drive style, drive-train and I have the wheels cantilevered. VEX axle is good to about one inch or so beyond the point of support without major issues. So I’m not to worried. I’m also working on creating a new VEX speed chart for the 269’s and the 393’s in high and low speed. I’ll continue to try different combinations and post about each of them here. I also was debating on using the new 2.75" omnis, that will be something else I’ll experiment with. Thank you for your response!!
An odd thing I’ve noticed about all omni wheels is that they appear to be slightly larger than their counterpart of the “same” size. It’s a very small difference, but in the past my attempts to make a 6 wheel configuration have failed because the omni wheels in the front and back positions cause the middle wheel (A regular 4in wheel, with the old or high traction tire, or 2.75in wheel) to be lifted off the ground. When you put it on the foam tiles it will sink in a bit, but it’s not as good as many would like it to be. If you do try the new 2.75 dual roller omni, could you tell us if they are also larger than the 2.75in wheel?
As for the drive you posted, personally I’d recommend using the largest drive sprockets practical in place of the small ones to minimize the chance of the chain slipping. I’m not sure if the next size sprocket up will be larger than the 2.75in wheel though.
Good Luck with your chassis though, and Kudos on using the small wheels. I like the small wheels too.
There is a way around this (aside from mounting the center wheel in an enlarged hole or slot), but it’s tedious and weird. If you want to blow off an hour or two solving this I can publish my Sekrit Solution.
Our team used the 6 wheel drive this year. I don’t know about any solutions taking more than an hour, but we simply wrapped a piece of nonslip tightly around the middle wheels. It worked quite well.
I had this worry too, But I wasn’t completely sure. Next meeting I go too, I’ll mic up the 2.75 new omnis in comparison to the normal 2.75 inch wheels. And I’ll mount the new ones on the bot to see if it touches at all and take plenty of pictures on all surfaces.
I was also thinking about using a larger chain sprocket and maybe even trying the low strength chain, doubled up, like Cheesy did last year. I’ll try both and post my results on here when I get there.
Thank you for your complements! :]
If you wouldn’t mind, could you publish this, I want to see what it is.
I basically ended up building a gearbox for each side with 1x5x1 C -Channel in the back.
