Well when you do a single 4 bar, you really have to have the table at the arms angle. That’s one of the reasons Owen and I stayed away from the single 4 bar and just did a 4 bar on each side. Also, how did you attach the 4 bar to the axle which will power it?
So there is no way to get the intake at a smaller angle than the arm? Well I stuck the axle collars on each axle and screwed a screw through the metal arm and into the axle collar. That kept the collar tight on the axle.
just a suggestion, screw two cogs into the back and run an axel through the arm, and into the cog, then power the axel using chain or gears etc (in or on the arm) … just an idea, worked well for us last year !
If our intake was lexan, I would need to cut a hole for the “tower” thing at the end of the intake. If I did that, I would have a big gap in the middle, maybe I can just have that “flap” be the same angle as the arm, and when the arm came up, the flap would fall down giving the intake more room…
Maybe it would work… Let’s think of a different solution first
If you have your mind set on trying out the single 4 bar, here are some ideas you could try:
I assume the “tower” thing you refer to above, are the 2 vertical bars at the front of your 4 bar arm? Your lexan intake ramp would need to fit over the top of these, so you would need to cut them, leaving only 1 hole extending above the top arm bar pivot hole. Attach 2 pieces of aluminium angle on the underside of your lexan, spaced so that you can bolt them to the top of the vertical front bars of the arm. You could then fix a 45° gusset on each side (or some other structure to create a triangle) to help hold the lexan ramp at the desired angle.
Can you make the lexan ramp any shorter at the back? (do you require the current full length to hold your full capacity of sacks?) as the shorter you make it, the shallower you can set the angle of it without it hitting the top of the arm (bearing in mind the lexan still has to reach the ground at the front).
If the lexan ramp is still too steep to operate well, you could consider lowering your tower so the top arm pivot point is at approx 10 inches. This will make the arm angle (and therefore the lexan ramp) a lot shallower. You would lose the ability to score the high goal, but you would gain the ability to drive under the troughs.
Another idea is to have it so that the front of the intake just sticks even further forwards (but folding back to fit in size). That’s what we did for our Worlds robot and it worked well, though to be honest, it meant the turning was pretty horrible as the front would swing so much
I’ll have a browse for some photos of our robot to explain myself better.
I found one picture of our robot that kinda shows what I meant, the picture is here: http://i.imgur.com/nmtmO.jpg
As you can see, the intake was very far in front of the robot (we did that mainly to score in the centre 30" from isolation easily).
If you look at the bottom of the arms, then follow the vertical beam up (the wide c channel under the intake), where that meets the intake tray has a joint. Everything in front of that joint pivots back to fit in size.
Yet another idea is to have something similar to what Oats (2941) had last year when they had a single set of arms (and like what 1107B used on their first robot). In this way you would start out with one single set of arms at the back, but they aren’t full length. From the ends of those, you build outwards, and then continue the arms as now two sets of arms, wide enough to fit the intake inside. Again, I will look for some pictures to aid the description.
I found one picture of the 1107B robot I was meaning that kinda shows what I was meaning. The image is here: [
Lucas came up with the “fourked bar” (forked four bar) idea post RWC last year. At the tower end, it is a short (~ 4 inch) single bar, but then there is a wide, cross-bar bolted to it and a piece of aluminium C channel arm fixed to both ends. It is the shape of a set of 2 pronged forks that wrap around either side of the intake. It allows the intake to be set at whatever angle you want.
Advantage - don’t have to worry about keeping 2 separate towers and arms in sync. Also, it was unique last year, which appealed to the boys, as they did not want to do any direct copying.
Disadvantage - it had to be reinforced with steel angle at the tower end, especially the cross bar which deformed under load on the first build. Not a big concern though, as this added weight is near the tower end of the arm.
Earlier when you released the videos i saw the chain bar worked pretty well. So i had a six bar before but decided to ditch it because it was too heavy and the chain bar was about a fourth of the weight. When i tried it i had problems with the chain stability when i get enough sacks whether it was because it was inaccurately made or what ever. In the end ironically a week before you released your pics i changed to a four bar which is now working very well. i made mine with two towers and two arm bars on each i would send you a pic but the robot is at the school. I mounted the lift in a bit of a hard to explain way other wise i would offer more assistance. If you have any specific questions how the to mount them i can do that until i get you the pictures.
A little off topic, but you may want to support the towers of the two bar more. Once you add any weight to the end of the two bar, the whole thing may just topple over, and then it won’t matter how you mount the intake.
Like the other commenters, I would suggest you use a four bar, and that you use the normal C-channels to lift. The fat C-channels weigh more than 2 regular C-channels combined (since the normal ones have the middle holes), so you’ll actually be saving a little weight.
Hmm… It sounds like you are putting the load of the arm on the axle itself. This has been known to cause severe shaft twisting… I would suggest bolting the arm to the sprocket/gear that is powering it. That way the shaft does not bear the rotational load of the arm, all it does is keep the gear and arm in place.
The advantage of switching to a linkage arm is that it’s easier to apply elastic, which makes it able to lift a lot more weight. For the sake of simplicity, I would have two towers and two arms, with the intake in between. It’s lot simpler and easy to build, and when your intake is mounted firmly, it helps keep the two sides in sync.
My issue with the chain bar was bending of the axle when the chain was tightened enough.
Why didn’t you just switch the chain bar to a standard 4 or 6 bar were you can support the intake on both sides.