rubber banding a single arm is actually quite easy if it’s range of motion is small enough. goofy arms don’t lift very far, so all you gotta do is add a little 4 bar attachment to the base of the arm, and you can band it there, and it’s a great place to add supports as well.
I find a lot of this to be quite misleading. You definitely dont need 2 V5 motors on a rd4b. It is really easy to rubber band a 2 bar as seen with 99% of starstruck robots. P loop is not a very good solution for a lift, you would need atleast a PI loop and most likely a full PID loop to make a lift run effectively. P loops can easily overheat a motor if their tuning is too high, and if you go any lower than that your movement becomes very slow. P loops work fine for small lightweight mechanisms, but quickly fall apart when tested on something load bearing.
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First off, I say two motors specifically for this year because of the heavy load that will most likely be carried. Ik that 1 motor dr4bs can and have been done (1320 tp). Second, the rubber band thing is my bad. I haven’t really looked at starstruck too much considering I started vex in ITZ. Lastly, I probs shouldn’t have said anything abt the code 
. Personally, I use a full pid loop but I heard somewhere that you could just use a p loop.
Sry for any misconceptions caused by my misunderstanding.
Thank you for your clarification.
So how much of the robot is aluminum, and how much is steel?
Also, what advantages did you see with using the 5-hole-wides on the base as opposed to regular c-channels?
There are some things I agree and disagree within this thread.
This really does depend. The main reason why my robot worked so well with one motor with 200 RPM and 1:7 gear ratio is because the lift, although looked bulky, was incredibly light (Seen in the reveal, they are using C-Channel Box bracing rather than X-Bracing, because it’s lighter and smaller) and the banding was tuned explicitly to be near linear with only two points. So, if you want your lift to be fast and only use one motor you need the following:
- Light field elements and in low numbers
- Lift that uses KEPS screw joints, in all places possible (Even through the gears)
- Lift has no more than 2 axles for its support, so you can track the position of the lift with a potentiometer
- Rarely use X-Bracing, as it is heavier and there are alternative, lighter methods that provide the same support (Such as C-Channel Box bracing, as seen in the video)
- Drill out the holes out of C-Channels that any axle or screw will go through, if the hole has a bearing flat screwed onto it
- Use regular bearing flats, with the joints and axles located in the middle of the 3 holes, as much as possible between two anchored points.
- You don’t need triangle bracing for your lift to be linear. In fact, triangle bracing, for the most part, makes the lift have more friction which will not be good if you are planning on doing one motor. You should be doing two point bracing in a manner that makes the lift linear.
If you lift up 10 of the cubes, you will be lifting up roughly the weight of TWO mobile goals, or 1 Mobile goal and 10-12 cones if you know the struggles from In The Zone. My cap bot only lifted 0.6 Ibs of weight. So if you’re planning on doing one motor you should be either doing 100 RPM 1:7 with one motor or 200 RPM 1:7 with two motors, and even that will likely be more or less a struggle for most teams. If you wish to copy my method of gearing if you’re attempting one motor, it will not work, as the HS gears are plastic the HS inlet will strip from all of the stress/momentum shifts.
Very intuitive thinking! But considering the repetitive shaking motion while moving how does it affect your autonomous? I cannot see the extra sensors on the robot, but I’m assuming you have tracking wheels?
It is definitely possible to rubber band a two bar. Look up StarStruck season and you will see plentiful examples on how teams rubber banded a two bar.
And most importantly, anything is possible with the right gearing or right support 
^ Agreed. And if you look in “In The Zone” you can even see methods of rubber banding for two bars that are capable of extending past 250 degrees of motion.
Considering the delicacy of handling cubes into towers during the matches, I have to agree with this.
I partially agree. Motors can even overheat even with PID because it doesn’t consider momentum/inertia compared to the force applied. This is where motion profiling comes in, but to be frank your robot should be built in a manner where the motor would never overheat even without motion profiling.
To be honest, even if the mechanism is lightweight you should always use PID. If the mechanism is light then it would be very easy to overshoot the position, hence is why PID exists to compensate and re-adjust from the overshooting.
I agree, and I would definitely suggest teams to do a 2 motor lift if they are incapable of following build quality techniques.
I used a P loop in StarStruck for my two bar, primarily because:
- My knowledge of coding was still developing
- I didn’t know what PID is
- The elements were massive so there wasn’t a need for something so precise
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Do you think a compound ratio like a 3:1:5:1 could work for a one motor dr4b?
If you are doing that compound ratio with one motor, I would consider this to be the most recommended way. The reason why the 36t gear is in the middle instead of 60t gears is primarily because there will be less torque applied to the axle, and the 60t gears on the lift would offer more support, rigidness, and height.
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But if someone is doing a 1:7 or 1:5 gear ratio with one motor, I would suggest doing:
Or maybe potentially:
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if you’re using a HS shaft, would it be acceptable to connect the follower gears across, rather than the drivers?
This is why:
This is why it would be better to connect both sides using 12t HS pinions instead of the plastic gears. The reason why I think @MasterCole 's suggestion would be an exception is because the torque is only a 1:3 gear ratio, nearly half of 1:5 or 1:7.
Edit//: I had to replace my gears twice on my Turning Point cap bot.
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hmm I understand. thanks, may have to reconsider my lift gearing.
I understand why a normal shaft on the driver gears is better, since it has less torque getting transferred through it, but will a normal shaft not twist at all from transferring one 100 rpm motors worth of torque across a large gap?
Looks at all of the low strength axles I have turned into drillbits
Sees 3674R’s “drillbit” from last season
Sees my puncher robot’s tilter mechanism nearly break from the torque of 1:1 100 RPM motor extending an axle across a large gap
I can confirm, 100 RPM motors are STRONG as heck, and they will twist a low-strength axle like nobody’s business even at a 1:1 gear ratio. 
not to entirely derail this topic, but one last question:
what is the best way transfer power from one side of a lift to another? HS shaft on your driver gears? that won’t exactly work, since all my 12T pinions are the ones with the 1/8" shaft holes, so no HS shafts on those lads. would using HS lockbars on my follower gears prevent them from getting stripped?
You can always get a solution by adding more. So if you have like 3-4 lockbars it should work. But I would suggest replacing the lockbars every 2-3 competitions.
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Would the HS axle by any chance twist under high loads? I’m thinking of lifting at least 7 cubes with one motor with a tray lift.
The original post says that this is the fourth robot, what were the last three and why the switch to a tray lift (if there was a change in design)?
we were running out of regular c channels.
currently there is a lot of steel stuff on our robot. we’ll reduce the amount of steel during our next rebuild
the anti tip only contact the foam tiles when the robot is going to tip so it doesn’t affect regular driving/auton. we have position tracking program but we haven’t put tracking wheels on our robot (running out of time). we’ll do that shortly though
well… I’m not sure if that will worth it. you can lift a lot of weight with the help of rubber bands, but rubber bands will also bend everything on your robot.
the first one is kind of like a tube (or a claw) intake that I posted at the very beginning of the season. We had a complete cad file for it, but before we finished building everything we decided to switch to a tray lift because rollers are the fastest/easiest way to intake cubes. The other two robots were all tray lift, but very different from the current one
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Aside from rubber bands, can you lift 7 cubes through sheer gear ratio?
I wish I could like a whole thread. There is some deep knowledge here.
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