pic: Recycle Rush Re-design Part 2

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I checked the weight of the main bot this morning, and it seems like I managed to bring it down to 86 lbs (probably some error), so I attempted to design a lightweight HP tetherbot.

Features:

weight of 15 lbs, not including tether chord and other electronics
1 RS 775 motor to 1:100 Versaplanetary
2 servos with delrin horns to serve as a retention system
accessible to other robots with an extending grabber arm or intake, so this could be used while the main bot landfills

This will be uploaded in the same folder as the main bot. See original post: http://www.chiefdelphi.com/media/photos/42570?

And as always, feel free to leave some questions and/or feedback!

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

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.

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?

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 :confused: . 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.

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?

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

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.

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.

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

http://www.powerwerx.com/_images/products/pp-contact-sizes.jpg

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

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.

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.

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"

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.

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.

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.

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.

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?