24-12-2015 22:46

pilleya

Re: pic: Recycle Rush Re-design Part 2

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

25-12-2015 00:40

Cash4587

Re: pic: Recycle Rush Re-design Part 2

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.

25-12-2015 00:53

pilleya

Re: pic: Recycle Rush Re-design Part 2

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?

25-12-2015 01:49

KohKohPuffs

Re: pic: Recycle Rush Re-design Part 2

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.

25-12-2015 01:59

asid61

Re: pic: Recycle Rush Re-design Part 2

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.

25-12-2015 03:04

KohKohPuffs

Re: pic: Recycle Rush Re-design Part 2

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?

25-12-2015 04:05

pilleya

Re: pic: Recycle Rush Re-design Part 2

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

25-12-2015 04:06

pilleya

Re: pic: Recycle Rush Re-design Part 2

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.

26-12-2015 03:11

Cash4587

Re: pic: Recycle Rush Re-design Part 2

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.

26-12-2015 03:30

Knufire

Re: pic: Recycle Rush Re-design Part 2

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

26-12-2015 05:23

pilleya

Re: pic: Recycle Rush Re-design Part 2

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

26-12-2015 12:17

philso

Re: pic: Recycle Rush Re-design Part 2

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.

26-12-2015 12:30

GeeTwo

Re: pic: Recycle Rush Re-design Part 2

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.

26-12-2015 22:46

Cash4587

Re: pic: Recycle Rush Re-design Part 2

If using only pneumatics for a thethered robot you will probably need more air tanks than it is worth to try to reduce the losses from long runs of wire. Lifting a tote with pistons requires a lot of air because of the weight of the totes in addition to the amount of stroke needed to lift them high enough. To stack at the feeder station you need to lift them considerably higher than the usual of about 13-14"

26-12-2015 23:03

GeeTwo

Re: pic: Recycle Rush Re-design Part 2

I haven't done the math, but I was thinking of a single large aluminum tank like this. Ten pounds of tank, but 7 gal (about 7 scf at 120 psi) of air.

26-12-2015 23:23

Cash4587

Re: pic: Recycle Rush Re-design Part 2

It might be doable. It would be hard to do, but doable. At some point though I think going the pneumatic route to try reduce weight on your physical tether would be the heavier option. The additional weight the tank and large piston or pistons would add in my opinion would be far more than a couple pounds of wire plus a versa planetary and chain loops.

26-12-2015 23:31

asid61

Re: pic: Recycle Rush Re-design Part 2

If designed properly, perhaps 16" would be enough. As long as the bottom tote just sits at the bottom and you only lift totes 2-6, you just need it to clear the chute- which is doable with 13-14" if you raise the bottom tote a bit, or just 16"ish.

26-12-2015 23:55

Cash4587

Re: pic: Recycle Rush Re-design Part 2

I would have to see it to believe it. I mean I don't doubt that it could be done but given the angle that the totes are entering the field, my team had to have a travel of about 25 inches in order for the tote being lifted to not interfere with the tote coming in through the chute. If we didn't lift it high enough the tote above it would be pushed past the point of being locked in place with the lip on the tote below it.

27-12-2015 00:14

pilleya

Re: pic: Recycle Rush Re-design Part 2

In long distance power transmission, a transformer is used to increase voltage to crazy high amounts. This reduces the power-loss and means that a less thick wire is required.

Obviously no custom circuitry can generate voltages greater than 24 volts, but is there anything stopping a transformer being used to increase the voltage at the motor controller, to compensate for the voltage lost during transmission. As long as it decreased down to 12 volts at the motor, it would still be being fed by 12 volts thus one motor controller

"R44 CUSTOM CIRCUITS shall not directly alter the power pathways between the ROBOT battery, PDP, motor controllers, relays,
motors, or other elements of the ROBOT control system (items explicitly mentioned in R55). "

Does increasing voltage alter the power pathways?

27-12-2015 01:02

GeeTwo

Re: pic: Recycle Rush Re-design Part 2

Let's start with a 7 gal (1617 cu in) charged to 117.6 psig (that's +8atm, selected to simplify the math). As we regulate this down to 58.8 psig (+4 atm), we are making 1617 * 4 = 6,468 scfm, or 1,293 cu in at +4 atm (58.8 psig). Multiplying this out, I show a potentially usable energy of over 76,000 lb-in. A tote weighs 7.8 lb, so that's about 9,750 tote-inches, or 5 totes times 1950 inches. If each lift is 25", this is still a total of 78 lifts. That's 78 lifts of 5 totes 25 inches. There were only 30 totes behind the walls, so even without doing any optimization beyond not pressurizing the down stroke, there is more than twice the required energy in one 7 gal tank to stack all of the totes behind the wall. (Though I haven't done any flow calculations to determine if it can be done in 2:15!)

With a 10 pound air tank, this obviously won't get down to 15 pounds, but I expect that it can be done for well under the available 35 pounds, including tank, cylinders, frame, tether, and electronics.

27-12-2015 01:12

GeeTwo

Re: pic: Recycle Rush Re-design Part 2

R18 is the list of motors, so that assemblies including motors do not fall under the CUSTOM CIRCUIT rules. Motor controllers are required to be connected directly to the PDP. I am 99+% certain that the GDC would consider a switching power supply which steps up from ~9V to ~12V would constitute "directly altering the power pathway". (OBTW, a transformer cannot be used to step up DC voltage; that's why Tesla's AC power distribution system eventually won out over Edison's DC system.) Consider the exceptions named in the second sentence of R44:
Stepping up the voltage is definitely consequential.

27-12-2015 01:25

pilleya

Re: pic: Recycle Rush Re-design Part 2

Thanks for clarifying the meaning of Power pathway. I thought that it meant that must be a direct pass-through without being interrupted by a sensor or relay etc. I was taking it in a rather literal sense.

27-12-2015 11:00

Ari423

Re: pic: Recycle Rush Re-design Part 2

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.

27-12-2015 13:35

GeeTwo

Re: pic: Recycle Rush Re-design Part 2

I agree that powering the down stroke with 15psi is probably worse than not powering it at all, but relying on a spring return or (if there's enough weight) gravity. Alternately, the two sides of the lift cylinders could be controlled through a 3-state solenoid or controlled separately so that you don't need to fill the upper chamber of the cylinders to 60psi, even though the supply is that high.

Yes, if you read more closely you can see that I was calculating based on the air in the tank above 60 psi.

That would make it even better on several counts - fewer than half as many lifts, as well as a lighter peak lift. The lift would have to be more than 25", however. Each six-stack would involve lifting 6 totes about 30", which is much less than lifting 15 totes 25". With a bit of optimization and some sensors, I estimate that five six-stacks would take about 3 gallons, or 3 six-stacks would need about 2 gallons of tank.

27-12-2015 17:49

Ari423

Re: pic: Recycle Rush Re-design Part 2

I think you're misunderstanding what I'm suggesting. The bottom of the piston's travel would be at the lip of the second tote on the stack. The piston would then travel up so the bottom of the second tote would just clear the top of the chute. Granted this is more than 25" of travel, but it's 12" less than it would be otherwise, you have to lift one less tote per 6 stack, and you only ever have to lift 4 totes at a time instead of 5. Therefore, since air consumption is lift force * lift height, you can decrease both lift force and height for an overall decrease in air consumption.

27-12-2015 22:26

GeeTwo

Re: pic: Recycle Rush Re-design Part 2

No, I understood, that you never need to lift more than four totes at a time. Perhaps I took your strategy even farther than you meant. Here's what I'm thinking as "making a stack":

• Drop two totes through the chute. The first lands on the floor, the second on top of the first.
• Lift those two totes high enough for the next step (about 30-36") (2 totes lifted)
• Drop two more totes through the chute.
• Lower the raised stack onto the stack on the floor, and continue to the low end of the stroke.
• Lift the four totes high enough for the next step (4 totes lifted).
• Drop two more totes through the chute.
• Lower the raised stack onto the stack on the floor, and continue down at least far enough to disengage from any totes.
• Open the release gate for the main robot to score it.

Six totes per stack when doing pairs is 2 for the first lift and 4 for the second lift; 2 + 4 = 6. Fifteen totes on single-stacking is 1 + 2 + 3 + 4 + 5. It doesn't matter where the lift engages the tote; the length of stroke must be as high as the bottom of the tote moves up plus the "engagement distance", that is the amount of motion between the bottom of the stroke and the tote being lifted off the floor. I'm estimating that to clear a 2-stack with a few inches for free entry of the second tote would be about 30-36".

If you were thinking of leaving a tote on the floor the whole time, that would be lifting 10 totes a bit over half as far as the six above. It's probably a wash in terms of air, but two lifts should take less time than four.

27-12-2015 22:40

EricH

Re: pic: Recycle Rush Re-design Part 2

That second bullet is where you missed him. The floor-level tote stays there to act as a catcher/ramp until the stack is complete.

28-12-2015 00:49

mman1506

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?

28-12-2015 08:10

GeeTwo

Re: pic: Recycle Rush Re-design Part 2

That would be "leaving the downstroke unpowered", which has been considered and largely discarded. Unless you have a separate mechanism to engage and disengage from the tote, your downstroke will have to work against some sort of spring action to get around the top edge of the tote. For reliable action, either the down stroke needs to be powered, or a spring return is needed, or the carriage must be heavy enough to force through the ratcheting action.

28-12-2015 10:22

Ari423

Re: pic: Recycle Rush Re-design Part 2

I was thinking of leaving one tote on the ground the whole time and stacking from there. Your way sounds like it could also work very well. Mine would use less air per cycle (shorter throw), but yours would use less cycles (2 vs. 4). I don't have the numbers in front of me to do the exact calculations. For anyone that does, it would be a wash if the height to lift a ground-level tote is double the height to lift a tote stacked 2 high to above the chute. If it's more, your idea uses less air; if less, my idea uses less.

Either way, your idea is almost definitely faster. You have one lift of two and one lift of four. I have that and also a lift of one and three. So either way, yours would have to be faster.

I just wish I thought of all of this during the season instead of now.


Also for the OP, if you do decide to go with pneumatics as GeeTwo suggested, you can move the PCM onto the tethered bot. Then you can decrease the tether to two wires (power and CAN). The power wire has a pretty low amperage when not running a compressor, so if you make it a big-ish wire you shouldn't see too bad of a voltage drop.

EDIT: One more thing for the OP. When totes fall from the chute to ground level, they tend to not land correctly because the front of the tote tips down as it comes out of the chute. Some HPs tried to negate this by pushing on the tote with the chute door as it slid down the chute. I see this as a big source of human error that should be avoided if possible. You may want to experiment with what base height will allow the bottom tote to land properly while still giving clearance for the second tote to fall on top of the first one. This will keep your human player's job down to a minimum, and it will also decrease the height you have to lift, which will decrease air consumption and lift time.

28-12-2015 11:05

Chris is me

Re: pic: Recycle Rush Re-design Part 2

Depending on the design, this can be pretty trivial. Hinge-style tote lifters have nearly no resisting force in the opposite direction and if the weight of the carriage alone doesn't do it, a tiny amount of surgical tubing would.

Powering the lift in one direction and only lifting the top 4 totes reduces the number of powered strokes required to stack to 4, with half the travel of lifting the bottom tote as well. It is also probably much faster to do this as it takes a long time for a tote to settle on the bottom level. I would have to run the calculations for air consumption but this could make 3 or 4 stacks with a reasonably small amount of air; several Clippard tanks would do it.

28-12-2015 12:36

mman1506

That's not hard. The weight of the shaft alone will probably be enough to overcome the friction of the cylinder. Anyway Ari423's reasoning for not powering the downstroke was not due to friction but due to the solenoids switching restrictions (what I'm questioning).

28-12-2015 13:17

Ari423

Re: pic: Recycle Rush Re-design Part 2

Well the reason I gave was solenoid switching restrictions, but it was actually more than that. We did devise a method of dealing with the solenoid. When we tried using in without any down pressure, it worked but it was painfully slow when only lifting one tote. Gravity just wasn't strong enough to overcome the friction (granted we also had a pulley system to make sure both sides were the same height that could have added some friction). We settled on about 15 psi of down force, which was below the rated min pressure but it worked out ok. Perhaps with a strategy where you lift 2 totes minimum you can get away with a lower pressure or even no pressure.

28-12-2015 13:29

Chris is me

Re: pic: Recycle Rush Re-design Part 2

You definitely either have too much friction, or you have the wrong flow control valve installed. This is a great application for one-way flow control valves, which restrict air going in but not out. My team had a stacking mechanism that would quickly and easily lower itself even without the weight of any totes on it; unless you have an extremely inefficient system this should work fine.

28-12-2015 14:13

Ari423

Re: pic: Recycle Rush Re-design Part 2

I can't quite speak for the mechanical aspect of the system, as I had no hand in that. I only worked on the control aspect of the system. And since I'm the only member of my team on CD, I don't expect we'll ever get a good answer as to why our system had so much friction.

I was under the impression that one-way valves were illegal. Is that not true?

28-12-2015 18:09

GeeTwo

Re: pic: Recycle Rush Re-design Part 2

In 2015, Rule R66 F allows (among other things) flow control valves as pneumatic components. Festo's page of one-way flow control valves describes the same thing Chris is describing - allowing free air flow one direction, throttled flow the other. There does not seem to be a rule allowing check valves, which allow air to travel in one direction but completely prevent airflow in the other direction. Apart from the interface between an external compressor and the robot, it is difficult to come up with an application for a check valve that complies with 2015's rule R78, which has been a game rule for some time:

29-12-2015 23:13

GeeTwo

Re: pic: Recycle Rush Re-design Part 2

I wanted to share my reasoning for putting the PCM on the robot side. Either way has benefits and costs relative to the other.

• The way I set things up, all of the wires carried simple DC signals that switched on the order of a second. CAN carries rather faster switching, so I wanted to leave it just on the main hull. I've since checked CAN lengths, and you should be OK running from one hull to the other, and even back. However, to simplify things and reduce losses, I would use an external terminator on the stacker end rather than bring the line back to the robot for termination at the PDB as most teams usually do.
• I didn't want to run CAN down the tether, because it's inherently more vulnerable. I was worried that if something happened to the tether, the whole robot might freeze up. If you are using PWM for motor control, this may not be an issue for you.
• I didn't want to run compressor power down the tether. There are workarounds, including a spike relay on the main hull side, and using a "tether bypass" when filling the tanks*. Still, much less current is required to power a compressor than some CIMs.
• Note that even with the PCM on the stacker hull, any limit switches or other sensors (except the pressure switch) still have to go back to the 'RIO. Limit switches and thoughtful design can significantly reduce the amount of air needed.

* I haven't found any rules in 2015 that would have prohibited making internal electrical changes (e.g. disconnecting the tether and wiring directly across it using molex or Anderson power poles) during pressurization process. Just make sure you put things back! The more steps in a checklist, the more likely something will get missed.