So after working for a month on design, 355A has finished it’s first iteration. However, it turns out 355A (me) will probably not be competing in VRC this year as I won’t have enough time when school starts. So since I wont be competing I figured there was no harm in posting the CAD pictures of the first iteration. This first post will include overall pictures of the robot and basic information on it.
Robot weighs approx. 12.5lbs without game objects, and up to 14lbs with 3 barrels.
Current object capacity on it is 3 objects, however this is missing the expanding top with axle’s on it to make it hold 5.
This is also missing a platform that is attached to the top by a hinge in the front. On the back of the platform a pneumatic piston is attached so that when extended, it tilts the platform up, creating a ramp so that you can quickly dump match loads/doubler/negator into goals.
The way the robot works is that the front roller on the manipulator slides up when it starts to hit an object. This will help situate it inbetween the conveyer belts on either side of the chute. The conveyer belts push the object up 7in so that there is room for the next one to be loaded. When it is time to score, the 3-stage lift goes up to the proper height and scores them out of the bottom of the chute. The goal of the manipulator was to make sure that it could:
Hold more then one object at a time
Score one object at a time
Make it so that the driver doesn’t have to do anything besides drive (no lifting up and down, no open close, etc.) This one was important as I thought it would save time when on the field and since I was a one-man team it would help a lot.
Sorry about the white space on the pictures, they got messed up.
I will upload more detailed pictures of the drive train, lift, and manipulator soon with more numbers and such.
Here are the basic numbers for the drive train.
It drives at about 4.797ft/sec
The motors run at an efficiency of 87.785% (50% is the optimum efficiency)
There is a 2.75" grippy wheel on the corners and a 2.85" VEXplorer wheel on the middle of the two sides. This creates a type of west coast drive.
There are 2 296 motors and 1 393 (@100rpm) on each side. The gear ratio is 4:1. HS Chain connects the 3 wheels together.
here is an encoder on each side of the drive train.
Note that the 48-tooth gear that should be on the middle motor axle (meshing with the 12-tooth gear) is missing because VEX does not have a CAD file of it and I did not have time to make one.
The lift is a 3-Stage Chain Vertical Lift. (If you don’t know what a chain vertical lift is, please refer to the 1103 thread for further education). All of the sprocket’s are 6-tooth HS except for the driven ones, which are 18-tooth HS sprockets.
The speed from floor height to 35in is 2.38 sec.
The two 393 motors (@100rpm) run at an efficiency of 83.33%
The two idler sprockets under the sliders (the ones with their own “metal box” is attached to the drive train, sitting in-between the motors on the drive train. The metal attachments and supports that connect the lift to the drive frame are not shown in any pictures.
Holy cow, our robot and your CAD robot look extremely similar. I’ll try and post pictures of ours soon.
Some questions since ours is uber similar. The lift, we use a two stage and reach 31" without a problem perhaps a 3 stage is unnecessary?
I think your drive is way too crazy fast. Unless of course you’re going to slow it down while the intake is raised. Ours runs at about 2 fps and will flip if accelerated back and forth while the intake is fully up. And ours is 16lb, with a very low CoG and lift located near the center of the robot.
Other than that I really like the design And nice CAD!
The sliding roller in the front has a low position height of 4in. It can raise to 6in. There is 1 296 motor powering the roller. The tank tread wheels would be covered with tank tread or friction mat, etc… whatever worked well once built.
The conveyer belts are 7in tall on the left and right side. They are powered by 1 296 motor and are geared/chained togeher to spin in opposite directions (obviously).
The third part like I said before would be a tilting platform to quickly load ans score match-loads,/doubler/negator. This platform would be attached to the expanding roof on the top of the chute.
While being able to pick up objects on the fly (just drive at the objects and let the robot do the rest), for driver and programming skills, you can raise the chute over the stacks of 2 and then lower over them to grab both at once. This manipulator created a robot that would be able to preform really well in matches as well as skills challenges.
Well it’s not over-running the motors and it isn’t so fast that you can’t control it, so I decided why not be faster then the majority of the field.
Thanks. I really appreciate that.
I could see part 2 being a “typical extending chute.” However part 1 is what many teams may miss or may have over-looked thus far. That takes lifting the manipulator up over the objects to score them out of the equation. Plus I can pretty much hit the object anywhere on the front of my robot and it will funnel into the chute. And I think the tilting platform on top is going to be a game-changer. Oh, I forgot to mention, that platform sticks out 1’ past the front of the robot, so you can dump objects/doublers/negators over the different walls and such. It could also be used for defence.
See beginning of post for this info.
I’ve been very curious to see what the VEX community would think of this so let me know.
-Nick
p.s. the team could still happen if someone is willing to “sponsor” my team and buy my parts list and ship it to my house within the next month. :rolleyes:
% of motor used (total motor stall torque)
------------------------------------------------------- = radius of wheel (weight of robot) (Coefficient of friction)
Gear ratio
gear ratio:
numbers over 1 mean speed. for example 4 would mean a 4:1 speed ratio aka gearing up
numbers under 1 mean torque. for example .5 would mean 1:2 power ratio aka gearing down.
Coefficient of Friction:
While some people in the VEX community out there are still trying to find the exact numbers, for our purposes .7 is pretty close for all the wheels for the most part.
If you use this formula for other things, such as a lift mechanism, do it exactly the same however drop out the CoF.
What if there is an object in a goal that is right at the 30in mark. Don’t you want to be able to lift above that so that you are capable of putting another object on top. Or what if you want to de-score an object that is 35in high? I thought out every possible situation and action the robot should do and made sure the robot was capable of accomplishing it.
I think when the lift is down, it’s fine. I’ve driven a robot this fast before and it’s still controllable. Being this fast will put you among the fastest bots on the field. The robot currently doesn’t have omni-directional movement so I’m making up for that with speed. I haven’t decided if I would want to slow it down when the lift is up. That is something I would figure out after building it and testing it out (therefore this would be part of iteration 2). However, if I did decide to slow it down, I would just program it to run the motors slower (less power to the motors) when it reached a certain height. This would be done using encoders on the drive axle on the lift, which I hadn’t yet put on the CAD model. The CoG is fine. I mean it’s not an inch off the ground, but unless I get rammed at 3’ off the ground, I won’t be falling over.
Thanks. I worked hard on this for the last couple weeks. Unfortunately that was before I found out I wouldn’t be doing VRC this year…
Thanks for the comments and such! Kepp 'em coming!
After seeing your picture, I do see some similarities.
The lift of course is very similar. This is pretty much because it’s the standard chain lift.
The shape of the drive train is similar.
The shape of the chute is similar.
Differences:
8 motors to 6 motors- and you were saying I was fast??? You could outrun anyone else on the field if you can keep all 8 on the drive throughout the season if you wanted to.
It looks as though you’ll have to lift the chute up and down to load objects. Could be fine if you have 2 drivers. I’m not sure if this will slow you down significantly in matches. This is why I had that roller in the front, so that I didn’t have to lift the chute up and down. I was actually influenced by FRC Lunacy robots and FRC breakaway robots.
It also looks as though you’re using pneumatics on the side to pinch the objects? I’m not sure. Can you let go of one at a time? I can’t completely tell.
It will be interesting to see what other major concepts will emerge for this game, as I’m sure due to just common sense and these early posts the vertical chute will be a common one.
Not too sure if I’d want to move fast in this one, I guess its more for pushing power. Saw 44 pushing robots out of the way in finals and it looked like fun!
As for our intake, I can see where you are coming from. A lot of really good teams seem to want to intake while driving. However looking at Lunacy the game objects were all the same and small compared to the robot so in some ways easier to use a roller intake to control them. Can’t wait to see how vertical intaking and hybrids like yours will play though.
I can agree the vertical chute will be a common one, it can be easy to drive and control.
As for the pneumatics I guess the way I’d explain it is it does a bit of both? It pinches and utilizes a roller intake of sorts. I haven’t been able to test it with multiple game objects yet, just the barrel but since the pneumatics are so fast it should be able to deposit one at a time.
This is very true. My plan was to go with it this fast into my first competition, and if I decided that it was too fast or I wanted to push more, then I would just change the gear ratio on it. It’s not too hard to change that so I’m not worried about it. I was also going to wait and see if I really wanted/needed a holonomic drive unti after the first competition I had, just so I could get a better feel for how the game would actually play out.
I expect there to be many/most of the chutes to be some kind of hybrid based off of the average design of one.
Definitely. This concept really takes KISS to heart. It’s like in Logomotion this year. Many times, the simple single jointed arms did better then the fancy rotating expanding arms or the vertical lifts because they were reliable and simple. However, when everything ends, Wildstang and Cheesy Poofs were still champions with their vertical lifts. I think there will always be common robot concepts for games. However, just using that basic concept by itself will only get you so far. It won’t take you to the world finals, which I hope is everyone’s goal in VRC. I feel like you have to at least put some kind of twist on the basic concepts to be really successful.
Potential issues with drive-train:
1 Have you run a 48t (wormwheel) to a 12t gear before? Any side-force issues due to the skew of the 48t gear?
2 Have you run 2.85 vs 2.75 diameter wheels on the same chain before? It seems like high COF would cause wheels running different speeds to bind…
3 Nitpick: “It drives at about 4.797fps” should include the word “calculated”, since you haven’t built and tested it yet.
4 “The motors run at an efficiency of 87.785%”. How did you calculated that? “50% is optimum” sounds like you are talking about %max torque rather than [efficiency = (VI in) / (rpmtorque out) ].
It’s not a worm-wheel, it’s just a normal gear. The 48-tooth gears were part of the wheel VEXplorer kit. All mechanical parts from VEXplorer are legal.
The difference in diameter is .1, so for VEX purposes they are running at such a slight difference in speed it shouldn’t cause a problem. I’ve heard from other people on the forum that this setup with these wheels runs well.
Fair enough. “Calculated Speed”
I suppose it’s not really efficiency. 0% would be free spinning- no friction. 100% would be total stall torque. Motors run at their best efficiency when at 50%, right in-between those two extremes. So 87.785% is telling you that you are closer to stall torque, but 87% is still low enough that it will last long enough through a match. I know there is a calculation to figure out exactly how long it will run for if you run it continuously but I’m not sure what the formula for that would be. And I’m pretty confident it will last the duration of a match.
My team was thinking of doing something similar to your intake i was wondering what the dimensions of your intake because i have been trying to figure out the best figures
re 48t vexplorer gears: What did you use for axle to axle pitch for the 48:12 gears? 12:12 is 0.5", 12:36 is 1", 12:48 should be 1.25", right?
I’ve considered custom Polycarb large sprockets to get N:1 speed up in one stage, rather than using 85% efficient gears followed by 95% efficient chains.
Sounds like you are talking about % max torque, rather than efficiency.
I think your eqn implies that you can spin your wheels with only 87% of max torque, while pushing the wall; was that your design intent?
I think nearly 5fps (calculated speed) on this robot is much too fast. #1 not needed, and #2 I think you are pushing your motors much too far.
I’m thinking that a single motor for your tank tread to lift the (up to) 5lb game objects is pushing it a little, as well.
I’m also thinking that your lift may be pushing itself a little too much, with only two High Strength motors at the speed that it is, and picking up 5 game objects. (max)
Just some of my thoughts/concerns, it just seems that you’re pushing all your motors too far. Also just thinking that a super fast drive will not really be needed in this year’s competition, and that strength will prove to be a little more important.
~Jordan
P.S. I was able to get the 48-tooth gear from the VEX Wiki CAD page; I think it’s in here.
I’m curious to see your design. I was thinking this would match many of the college isolation robots. But since this is high school I made sure it could hold more due to the interaction zone.
I don’t have the CAD files on this computer so I’m going to be using memory here…
Each drive train side is 3" wide. The whole robot is 17.5" wide overall. There’s about .5" of room on each side in-between the manipulator and the drive sides. I believe the whole manipulator is 10.5" wide. The inside (chute) metal wise is 6.5" wide, With the conveyer belts at 6.5in apart too. Deductive reasoning ftw. Hope that helps.
The front roller I have is powered by a 269 motor. The sliding up and down of it is free, using gravity. I’m not sure whether oyu were referring to the spinning of the roller or the sliding of it.
And nice CAD!