pic: Recycle Rush Re-design Part 2

[KohKohPuffs]

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[pilleya]

Great looking design, I came up with a similar thing on paper before one of our Off-season events, didn't end up building it though.

My weight calculations were about 18lb, with a 10:1 VersaPlanetary with CIM(belt drive with 24t pulley) with the Igus Linear guides that were available in FIRST choice 2015(were also available in 2016).

I also thought about having it sitting on a thin plastic sheet, like HDPE, Delrin or Polycarbonate to reduce friction and to make it easier to intake the stack, especially for landfill bots without touch it own it intake wheel systems

[Cash4587]

Please keep in mind that on most powered feeder stackers, the voltage drop is pretty significant over 25ft of tether. I can't speak for 148, but for my team and 1296 (if I am not mistaking), we had to use 10ga wire to get enough voltage. We also had to go with a 25:1 on a cim motor to be able to lift totes 4 totes fast enough with enough power.

[pilleya]

That is a very good point, hadn't though about that. That is very interesting to think about.

What 10awg wire did you guys use, and how well does it fit into a 45a powerpole?

[KohKohPuffs]

Originally Posted by Cash4587

Please keep in mind that on most powered feeder stackers, the voltage drop is pretty significant over 25ft of tether. I can't speak for 148, but for my team and 1296 (if I am not mistaking), we had to use 10ga wire to get enough voltage. We also had to go with a 25:1 on a cim motor to be able to lift totes 4 totes fast enough with enough power.

Oh right, when I was in 115, we started out with one 775 and I believe a 1:100 reduction, and that was barely able to lift up 6 stacks. Although I calculated my scenario to do the job in 3 seconds (the main bot stacks much faster).

As for voltage... I never considered that actually . If it's a 10 gauge wire it's going to be bulky... and that means more weight. I guess I can remove the can burglars if I'm going to add this with the main bot.

[asid61]

Originally Posted by KohKohPuffs

Oh right, when I was in 115, we started out with one 775 and I believe a 1:100 reduction, and that was barely able to lift up 6 stacks. Although I calculated my scenario to do the job in 3 seconds (the main bot stacks much faster).

As for voltage... I never considered that actually . If it's a 10 gauge wire it's going to be bulky... and that means more weight. I guess I can remove the can burglars if I'm going to add this with the main bot.

Depends on the pulley diameter. We used a 1.06" diameter pulley with 2 RS-775s at a 21:1 reduction to get optimal speed on 6 totes, and that with a very long lever arm adding friction. 254's lift on slightly smaller pulleys was 2 775s on ~12.5:1 reduction and was very fast, due to the much lower friction/ smaller lever arm.
A single 775 going to a similar pulley would only need maybe a 50:1 reduction even with a long lever arm. If you place it nicely you could get away with a 25:1 or 30:1 reduction.

You said you are using servos to hold the totes; why not just use the arm? FRC-legal servos are very weak.

[KohKohPuffs]

Originally Posted by asid61

Depends on the pulley diameter. We used a 1.06" diameter pulley with 2 RS-775s at a 21:1 reduction to get optimal speed on 6 totes, and that with a very long lever arm adding friction. 254's lift on slightly smaller pulleys was 2 775s on ~12.5:1 reduction and was very fast, due to the much lower friction/ smaller lever arm.
A single 775 going to a similar pulley would only need maybe a 50:1 reduction even with a long lever arm. If you place it nicely you could get away with a 25:1 or 30:1 reduction.

You said you are using servos to hold the totes; why not just use the arm? FRC-legal servos are very weak.

So I'm using a 1:100 reduction, and the elevator runs on roller chain with 16T sprocket ends. I recalculated with a 1" diameter, and it looks like this thing is going to be much slower than expected. But then again, I imagined the strategy of this would be to have this for other bots while the tethered main bot works on the landfill, assuming weight limit allows for this and the main bot.

Really, the servos are just to keep the first tote from sliding too far out. Also, the servos are MG-995s and a stress test video on YouTube showed that they are decently strong for this purpose... on the other hand I'm not sure if those servos are FRC legal, is there a list somewhere of what is legal and what's not?

[pilleya]

Originally Posted by KohKohPuffs

Is there a list somewhere of what is legal and what's not?

In 2015 there wasn't a list of particular servos that were legal/illegal

"PWM COTS servos with a maximum power rating of 4W each at 6VDC
Per the Servo Industry, Servo Max Power Rating = (Stall Torque) X (No Load Speed)"- straight from 2015 game manual

[pilleya]

For the official season, we used a mini-cim and a 12:1 gear ratio on our stacker. Before our first Off-season event we converted our practise robot into a landfill bot, with a CIM and a 10:1, this was driving a spool and rope to stack, as we had broken the timing belt. We were getting 2 landfill stacks or 2 human player stacks from this robot.

After we saw that a full size CIM would give us extra stacking speed, we upgraded our primary robot to a 10:1 and CIM. At Champs we were putting up 3 HP stacks. In practise for the Chinese Robotics Competition with our rather crude chute mockup(allowed faster feeding of totes) and smooth floor, we were managing to put up 5+ stacks with bins on two of the stacks, legend has it that at in one practise session we put up 6 stacks 2 with bin . However like many things in the 'heat' and pressure of the competition, that number decreased to around 4.

Something else to think about is the use of surgical tubing to assist in the raising of the stacker with a heavy load, it worked great for us this season.

[Cash4587]

Not exactly sure what wire we used, we had to source it from a wire company here in Houston. 10ga barely fits in the 45a anderson connectors, we may have cut a few of the wires off the ends to make them fit. To give you an estimate of about how much our tether weighed, it was around 3lbs IIRC but it included the nylon sleeving as well as a 25ft Ethernet cable (the Ethernet cable was for the encoder and limit switch we had on our tethered bot to give us feedback for PID, we chose an Ethernet cable because they are easy to replace) It is not necessary though, I think 148 just bang banged it.

[Knufire]

Originally Posted by Cash4587

10ga barely fits in the 45a anderson connectors, we may have cut a few of the wires off the ends to make them fit.

Strange, we haven't had a problem with this.

[pilleya]

Well the KOP 12awg wire seems to not fit in a 30amp contact.

The other issue is the insulation, the insulation of the sp and SRX wire barely fits into a 45amp connector. I'm not complaining though, I love the wet noodle wire its just fantastic, and so amusing to play with. Definitely need to get some to wire the drivetrain of our 2016 robot

[philso]

Not all wire of the same nominal gauge has the same conductor outside diameter. The "wet noodle wire" could be a high-strand count, extra flexible wire such as DLO where the conductor and insulation OD is larger than with the "standard" wire of with the same nominal AWG.

When crimping the "closed" contacts on the wire, if it fits in the hole, it is most likely Okay. With the "open" type shown at the right of the photo linked by Knufire, it would be best to check with the manufacturer of the contact what conductor diameter range (in inches or mm) their contact is meant to work properly with. At the very least, do a bunch of sample crimps, say 5 or more, and do a pull test on each one to ensure that the two "wings" are holding the conductor securely. Of course, you would also want to make sure the wire and contact assembly fit properly in the housing. Just a warning, the larger conductor sizes might cause a ratcheting crimper to jam part way and not be able to complete its cycle.

[GeeTwo]

Trying to figure out ways to reduce losses down the tether, I came up with a concept for the stacker that allows a very light tether; it would only need to carry signal-level information.

• The mobile robot is all-electric (that is, has no pneumatics components apart from the PCB).
• A large (probably aluminum) air tank and all of the "on board" portions of the pneumatic system except the PCB are on the tether/stacker bot. All of the actuators on the stacker are pneumatic (probably just a lifter and a hold/release to access the stack.
• The compressor is located "off board" the robot. When filling the tanks, the electrical connections are run "short" from the PCB and the air connections are run "short" to the air tank.

To conserve air when lifting short stacks, I would recommend a limit switch on the lift and either a 3-state pneumatic solenoid (pressurize, closed center, vent) or a separate "keeper" pneumatic cylinder that holds a lifted stack.

Presuming that the tank will store air at/near 120psi (making it half as large as if it stored 60psi), and using a 3-state solenoid valve for the lift and a single solenoid valve for the release, I count 5 pairs of signal wires down the tether:

1. Pressure switch
2. Lift Limit Switch
3. Pneumatic Lift
4. Pneumatic Lower or Hold
5. Pneumatic Release

Edit: Of course, additional sensors (tote presence, state of release, state of hold/lower) would add a bit more to the tether.

[mman1506]

Originally Posted by Ari423

We went the pneumatics route this year, so I have some first hand results as to how our testing went. Not powering the downstroke sounds like a good idea until you learn that most solenoids need 20 psi minimum on each side to open and close properly. We eventually decided on 15 psi, and it was still very slow going down. Also, don't forget that once your tank drops below 60 psi, you will see decreased performance. For this reason, we went with slightly bigger cylinders at 30 psi so we wouldn't see that effect until later in the match. No matter the size of your air tanks, at 60 psi you will see that effect halfway through your lifts.

Also, if you did what many teams did this year and let the second tote fall into the first one without lifting the first one, you will only need to lift 4 totes per 6 stack, not 5. You also won't need to lift them as high, only from 1 tote high to above the chute instead of from the ground. IIRC that's less than 25". Or you could do what we did and build a ramp attached to our stacker for the totes to slide to (almost) ground level, then you only need to lift the height of one tote.

Why didn't you just leave a port on one side of the pneumatic cylinder open and put a plug on the unused port of solenoid?