Messages

1

Progress Reports / Re: Last Minute Robotics - Adrian Kelly

« on: August 09, 2015, 05:04:19 pm »

I'm sorry, I used the wrong word. I meant removable, but the horns sliding through idea is genius.

I agree, but I can't take credit for it. Somebody suggested it at Bot Blast when I brought up the issues with horns, and I can't believe nobody's done it before.

You noted in your Bot Blast recap that the screws had started to pull out of the frame. Would you recommend a different way of connecting armor to UHMW/HDPE frame rails? (Something like Fingertech's nutstrips, maybe?)

Yep, the screws had pulled out about 1/16" and the wedge was loose. It might have been the screws loosening, but I'm worried about the threads in the plastic failing after a few more vertical spinners. Nutstrips might work better, with screws going all the way through the UHMW, but I'd still be worried about those holes stretching if they're close to the edge. A block of metal between the wedge and the nutstrip would push them back and solve that problem, but the only real advantage of UHMW is that it is thick enough to put screws in directly. I would either move to a larger screw size and make some backup rails, or use nutstrip and a thinner, stronger armor.

For Sisu, I've been looking around at what other people make their ants out of, and the bent aluminum method seems interesting. Brushless outrunners are lighter than the 280s that come on the 1000rpm motors, and also shorter so that I can make the chassis narrower. Along with switching to a 1mm titanium wedge, this thing is now down to 0.82lbs, and it's only missing the nutstrip. With the extra weight, I would increase the wedge to 0.0625", but I haven't found a good supplier yet as Fingertech only goes up to 1mm. I could also change the 1/16" UHMW wheelguards to 0.5mm Ti. The center of gravity is also a little too far back. I can't move the motors back any more because of the wheelguard. Without wheelguards this robot would be laid out a lot better. Would sticking the wheelguards out past the back of the bot make them more vulnerable?

With motors this big in an ant, I'm anticipating this thing being hard to control, and so I'm going to try to make my own gyro/mixer that can be used upside down, using a multicopter flight controller like Lucas Grell suggested. The OpenPilot Atom happens to have exactly the hardware I need: a microcontroller, RC inputs and outputs, a gyroscope and an accelerometer. It has open source software, and for 4g and $25, seems pretty awesome. We'll have to see how much of their software I can reuse.






For Mad Props, NERC has emailed me back confirming that I won't get any weight bonus, but Bot Blast has not. For NERC I'm definitely going to put bearings on the bottom to make it roll smoother, and hinged wedgelets on the front. I couldn't figure out a way for it to self right when it's stuck on its face, except running one prop backwards to fall on its side, which I doubt there will be enough thrust to do, so I'm designing in a self righting arm on a servo. I think this will let me get rid of the large, heavy, and fragile self righting hoops, at the expense of slower self righting.

And I finally got to do a bit of work on Whirl and Hurl. The motor mount is mostly done, and the top and bottom plates are cut and still need to be rounded out some more. It's a ridiculous amount of aluminum. Drilling through the motor mount took 4 hours on my 1/4hp drill press and the brand new bit is now totally dull. For the wheel issue, I'm thinking of putting steel washers on either side of the wheel to help protect it, or Gene brought up using an RC car wheel with foam tread and a plastic hub.

2

Questions / Re: Brushless Drive - Ant/Beattle

« on: August 03, 2015, 10:15:15 am »

Gene posted this video yesterday of faster, smaller brushless motors on his 6lb undercutter. It looks like he just switched from the 28x34mm 1100kV Lumenier outrunner to their smaller and faster 28x25mm 2000kV outrunner. Looking through his Facebook page, he's gone through a lot of motors, including some Hobbyking inrunners and Castle Creations inrunners. It's an interesting progression, and the sensorless motors seem to be working for him.

Hobbyking Motors

3

Skills / Tips & Tricks / Re: Chinese 25mm Gearboxes (For Beetleweights)

« on: August 03, 2015, 01:23:04 am »

I just tested and then took apart my 1000rpm motor with the plastic back that I bought on eBay in 2013. For stall current, I tested at 1V because apparently I blew the 10A fuse in my meter. When the motor was cold, I got 175mA, or 2.1A at 12V. Over the next 30 seconds, current rose to 225mA, or 2.7A at 12V, as the coils heated up. The motor can was still cold to the touch. These seem in line with Ian's measurements of the 500rpm eBay motors.

When I opened it up, the gearbox had three sets of motor mounting holes, with 14, 15, and 17mm spacing. Its a shame there's no 16mm spacing, as that's a common dimension for 24mm brushless inrunners. I wonder if it would be possible to expand the holes slightly to fit.

4

Questions / Re: Brushless Drive - Ant/Beattle

« on: July 30, 2015, 04:54:21 pm »

You're right, they all have two bearings, I was referring to the rotor. While a few have a skirt bearing like the motor below, most do not, and so a shock could bend the rotor until it hits the stator. I don't have enough experience to know if this actually happens or not.

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Questions / Re: Brushless Drive - Ant/Beattle

« on: July 30, 2015, 04:37:30 pm »

(Post moved from my build progress thread, so that we can keep all the info together.)

It looks like the cheapest source for gearboxes is just to buy chinese gearmotors, like what Harry did. This thread says they have 14.8:1 and 24.7:1 ratio version, and they all have both 14 and 17mm spaced mounting holes. The 24mm inrunner I have has 16mm mounting holes, and it looks like most 24mm inrunners have both 16 and 19mm . Hobbyking seems to have 12mm and 20mm inrunners that seem about right for ants and beetles respectively. Maybe the 12mm ones would fit on these gearboxes, which look a lot like Silver Sparks with shorter motors and shafts. On much bigger bots, I've seen people use the Banebots P60 gearbox.

I found some other details of people using brushless drive in the Facebook group. This was posted yesterday, and Russ Barrow seems to be experimenting with brushless a lot. He put 12mm inrunners in 13mm Maxon planetary gearboxes for his 3lb Dark Daggers, and made some custom gearboxes out of steel tubing and an outrunner for his 3lb Dark Pummeler.

It looks like SimonK, the open source ESC firmware I'm using on my melty, is the way to go, apparently it gives better reversing than most car ESCs. Here's a list of ESCs that are known to work, it looks like it's just airplane/quadcopter ESCs. Car ESCs have bigger heatsinks, but for I'm not using the heatsink and bolting the ESC to my aluminum frame, which should give better cooling for less weight (what's the point of a heatsink inside a sealed box?). I flashed my F-60A ESC with the KKMulticopter Flash Tool, a USBASP programmer, and this awesome tool which let me do it with no soldering. Make sure to enable COMP_PWM for regenerative braking, and RC_PULS_REVERSE so you can go backwards. This ESC from the same series is tested with SimonK and looks about the right size for the 12mm motors, or this ESC for a 20mm motor.

With outrunners, you get more torque and less speed, but I don't think they have enough torque or shaft strength to use without a gearbox. Most outrunners are only supported on one end, while inrunners have bearings on both ends, and so should hold up to shock better. And an inrunner more stages of reduction gives you more play in your gears, which is actually helps a sensorless controller know what position the motor is in and will give you better performance.

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Skills / Tips & Tricks / Re: Chinese 25mm Gearboxes (For Beetleweights)

« on: July 30, 2015, 04:10:56 pm »

Yes, thank you! Does your non-kitbots one have a plastic or metal back? Is there anything else we can use to tell the high and low power ones apart? I can test my plastic back ebay motor for the stall current when I get home.

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Progress Reports / Re: Last Minute Robotics - Adrian Kelly

« on: July 30, 2015, 03:52:00 pm »

Kevin used much smaller brushless motors on those boxes in his 3.4 lb wedge part of a multibot, and it could push 15s around. Those are probably way overkill. Sensorless DOES work for drive.

Wow, that's a lot of power and good to hear. I wasn't thinking of using these motors in an ant.

I'm also curious about brushless for antweight drive motors -- are there any resources about that online?

I wrote a big paragraph here, then moved it to the brushless drive thread so we keep all the info together and don't clutter this thread up too much.

I've used a differently geared B16 on a titanium ant, so it's possible to use that size motor.   Also, I've never used them, but Technobots has 22mm and 16mm motors with planetary gearboxes.   They're in the UK, though so shipping is a bit high.

Thanks. The Technobots 22mm motors look pretty good, except they don't have any gear ratios between 128 and 2000 rpm

If I were you (which I'm not), I would make sure that Sisu 2.0's horns are interchangeable.

By interchangeable, do you mean between left/right? Or that when I flip over, they slide through the frame so they stick out the other side? I was planning on doing both, and removing them against horizontal spinners.

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Progress Reports / Re: Last Minute Robotics - Adrian Kelly

« on: July 30, 2015, 12:50:31 am »

Mathias, Mad Props is definitely for the entertainment value, because I thought it would be fun to build and drive. I'm not expecting it to win any competitions, but I'm trying to make it as competitive as possible given the ridiculousness of the idea. I was looking into bearings mostly just for the lower friction. They would let the robot move a lot faster than PTFE or UHMW skids, which is what I was thinking originally, but the SPARC rules are very clear that I would lose any weight bonus, even if the wheels were unpowerd.

Travis, I don't think this would count as a flying robot, as it wouldn't have enough thrust to leave the ground, and in the normal orientation, wouldn't even generate any lift. The rules are a rather unclear on how much of a weight bonus this would get, I made a thread for it here, but I do think I would qualify for some.

And yes, Blutsauger did put two wheels on each side. It looked like they lost one to Gyroscopic's drum, and another to a hard landing. I believe on the far side, the hub is still on. The shaft snapped right between the two wheels, and was bent at the gearbox. He also said said his ESCs were also not calibrated correctly in our fight, and so he was driving at less than full power.

I rehashed my original idea for Sisu, that was too complicated of a frame design to build with my limited tools, and added what I've learned from making the first one. The only parts that would carry over would be the receiver and battery, so it's more of a spiritual successor. Also, when I calculated it last time I was very close to the weight limit and didn't want to risk being over, and right now I'm at 0.93lb with no receiver or speed controllers. The 1/16" aluminum wedge, 1/16" garolite bottom wedge, and 1/16 UHMW rear plate are all rather thin.





These motors are a little too large to realistically fit in an antweight, but the 16mm Silver Sparks were not enough power. Does anybody know of a good gearmotor about 20mm in diameter? Or any small sensored brushless motors?


You can see why I would have to redesign the frame.

I also noticed that the 24mm brushless motors I got for Whirl and Hurl are the same diameter as the brushed ones on the 1000rpm ebay motors. I think the bolt holes are the same, so I could do brushless drive, but I haven't been able to find any sensored inrunners under 36mm, and I don't think sensorless drive is a good idea. I know a lot of small RC cars do it, but they usually don't get in pushing matches with other cars.



Charles mounted external sensors on outrunner motors, but with inrunners, I think you'd have to put the sensors inside the can, and they're usually better sealed than outrunners. If I used outrunners, I'd be worried about the frame flexing and hitting the spinning shell. Is there another reason why I never see outrunners used for drive?

9

Progress Reports / Re: Last Minute Robotics - Adrian Kelly

« on: July 28, 2015, 03:04:23 am »

Ooh! I was worried about spinners tearing Mad Props apart, but I could pull a Bite Force and put a wedge on the back when I need it!

10

Progress Reports / Re: Last Minute Robotics - Adrian Kelly

« on: July 28, 2015, 02:52:08 am »

Here come the pictures!

Sisu


The Bot Blast Antweight lineup


Sharpening the wedge and waiting for fights to start.


Blutsauger 30 minutes before our fight, after facing Gyroscopic. I did find a video of this one, which happened to be my most interesting fight of the day.


After the event




Blutsauger put some nice dents in my wedge. You can see in the other photos that the screws are starting to pull out of the plastic too.


Those sawblade things were hilarious


The back is pretty much unscathed, with a few scratches from the saw


Whirl and Hurl

The original CAD model, for the unibody chassis.




Sexy, isn't it.


And the backup plan. All the same internal components, and a slightly heavier and weaker chassis


I didn't quite finish this CAD model, there was supposed to be a wall to keep everything from sliding into the wheel.


I literally left it like this when I went to Bot Blast


All the major components


The board that controls it all


With the accelerometer mounted on the back


And this is what made me stop working on it. Even after straightening out the wheel as much as possible, there's still a big tear from when it exploded.


Mad Props
CAD model for the 4.5in blade version, currently weighing in at 2.8lb.





Everything is 1/8" Aluminum, except the bottom, which is 1/16". I still need to figure out the bushings and blade hubs, and how to put bearings sticking through the bottom to minimize friction. But first, I need to decide on a weight class, which means figuring out which events, if any, will give this robot a weight bonus. The NERC rules specifically say no weight bonus, and SPARC says 100% bonus in one place and 50% bonus in another. I'm thinking maybe make it 12lb, to compete in the 12lb class at Motorama where they use NERC rules, and in the 6lb class at Bot Blast next year, where they use SPARC, if they will let me. Adding bearings might also hurt my weight bonus chances, but if I don't have them, I would need to step up to 6" props on a 3lber, and it's flimsy looking enough as it is.

I've been looking at prop design as well, and it looks like quadcopter props like these 6" ones will work well for testing. Unlike plane props, as they're designed to exert a static thrust while hovering. Plastic props would be a lot safer to practice driving with than my S7 blades. And a 3lb bot could lift off with two of those at 22,000 rpm

In addition, thrust goes up in proportion to rpm^2 and diameter^4, while diameter goes up in proportion to the cube root of weight. This should mean that larger bots have a larger thrust to weight ratio, or can devote less of their weight to the drive system. Also, in order to get a large bite, I want to keep the rpm down under 10,000, but most planes and quadcopters keep their maximum tip speed around 200m/s for maximum power, meaning the optimal prop is in the ballpark of 15 inches in diameter. That would be one hell of a bot.

I also modeled the self-righting capabilities of those hoops. The robot rotates around the line as it rolls, and the sphere is the center of gravity.


The thing sticking out is to keep it from sitting on its back.


Once I get this built, I need to see if I can self-right from that position without it, using one prop to fall on its side. And how do I self-right from a faceplant? I think it would be lighter too to use UHMW hoops like on Totally Offensive. Or I could have one long hoop and make the whole robot an EDF!

Alright, this post is long enough. I might have a few updates on Mad Props, but I won't be able to do any building for a little while The week of the 10th should be Whirl and Hurl week though!

11

NERC (Northeast Robotics Club) / Re: NERC Franklin Institute 2015 Event

« on: July 26, 2015, 10:52:34 pm »

I'm thinking about making a non-wheeled propellor-driven robot, which SPARC gives a weight bonus but NERC does not.

12

Rules Discussion / Re: Weight Bonus Ambiguity

« on: July 26, 2015, 10:47:20 pm »

Yep, I'm talking about a bot with two props, and no wheels. I think I'm pretty clearly in the Non-Wheeled Robot category, the two documents just conflict on how much weight bonus I get.

13

NERC (Northeast Robotics Club) / Re: NERC Franklin Institute 2015 Event

« on: July 26, 2015, 06:07:52 pm »

Will Franklin Institute follow the SPARC or NERC ruleset? Does anybody know about Motorama?

14

Progress Reports / Re: First Antweight (Name TBA)

« on: July 26, 2015, 05:42:53 pm »

I'll have to look into a receiver, as I hit my first snag last night while hooking everything up: the Spektrum receiver requires the ESC cables plugged in vertically, and once they're plugged in, it is at least 1" or longer on each side (with reasonable room for the ESC cables to bend 90 degrees) -- making the inner height of the chassis more than what I'd imagined for the outer height (somewhere closer to 3/4" outer height.) 

I've faced that issue before. The R410X cables plug in parallel to the board, which is nice in a short chassis.

As far as the battery, I might actually go for something NiMH or NiCad 7.2V RC car pack that is much larger in volume, to start. Why? Because this wedge bot will likely end up being driven by kids at the local Maker Faire in September on a mini sumo ring (against the autonomous bot, and anyone else's mini sumo robot that I can get to come that day.) The lipos, even at 460mAh, probably aren't gonna outlast the kids' excitement to drive a robot around, and at 7.2V the speed will be a little bit more manageable (I may limit the "servo range" in my controller, too, to slow it down.) I may save the turnigy 460's for a different project or use them on a mini sumo bot, since they'd be plenty big for all day runs in mini sumo.

I agree with Badnik here, the lipo will be plenty of runtime. When you're driving for a long period of time and you don't need to fit in the weight limit, you might want to put a lipo alarm in to make sure you don't drain your batteries all the way, but I would stick with the lipo.

Since I'm not factoring in a spinning/drum weapon, weapon motor, and mounts like the latter 2 have, I feel like I can beef up the chassis and armor to make something that can be driven around all day and into walls repeatedly (which will be some of me driving and some of when I let kids drive it, but mostly me, hah.) Which, for a first build as a learning experience, seems like a pretty good idea.

Sisu question -- are there any videos of its bouts from Bot Blast 2015? I checked Youtube but didn't find anything.

That's exactly what I did. Build a simple bot first to get some driving practice, and make sure you can't break it if you tried. I couldn't find any videos on Youtube either. It looked like everybody just took videos of their own matches, which is what I did. I'll see if I can upload them tonight.

15

Rules Discussion / Weight Bonus Ambiguity

« on: July 26, 2015, 04:59:41 pm »

I'm thinking of building a propeller driven robot which would slide across the floor with no wheels, and was wondering what weight bonuses, if any, a non-wheeled, non-shuffling, non-walker robot would get. Under the Tournament Procedures v1.0, the categories are Walkers, Shufflers/novel non-wheeled robots, and everything else. I would either get either no weight bonus, or a 50% bonus, depending on if the event organizer determines I am a "novel non-wheeled robot." However, under the Robot Construction Specifications v1.0 section 4, it is seems to say that I would get a 100% weight bonus for having a non-wheeled robot. Also, walking, shuffling, hopping, flying, and hovering robots would seem count as a non-wheeled robot and get the 100% weight bonus, but also have their own categories. Can somebody clarify this? Can we update the next version of the rules to make this more clear?

There is a 100% weight bonus for non-wheeled robots (There may be a 50% weight bonus for shufflers or other forms
of locomotion which do not fall within the definition of non-wheeled robot - see 5.1.2 for
a definition of a non-wheeled robot.)

Methods of mobility include:
5.1.1. Rolling (wheels, tracks or the whole robot)
5.1.2. Non-wheeled: non-wheeled robots have no rolling elements in contact with
the floor and no continuous rolling or cam operated motion in contact with the
floor, either directly or via a linkage. Motion is “continuous” if continuous
operation of the drive motor(s) produces continuous motion of the robot.
Linear-actuated legs and novel non-wheeled drive systems may qualify for this
bonus. If you are intending to enter a non-wheeled robot in any event contact
the event as soon as possible to determine what if any weight bonus you will
qualify for.
5.1.3. Shuffling (rotational cam operated legs)
5.1.4. Ground effect air cushions (hovercrafts)
5.1.5. Jumping and hopping may be allowed at some events, contact the event
organizer if you’re intending on using this as a method of locomotion.
5.1.6. Flying (airfoil using, helium balloons, ornithopters, etc.)may be allowed at
some events, contact the event organizer if you’re intending on using this as a
method of locomotion.

Walkers may weigh up to 100% more than their standard class weight limit.

Walkers are those robots in which multiple linear or limited-travel rotary actuators are
intermittently driven to produce linear travel of the robot. Actuation may be through electric,
pneumatic, or hydraulic means. Walkers must have no parts normally in contact with the
ground undergoing continuous rotation, and must require some change in timing or
sequencing of the driving mechanisms in order to reverse direction. Walkers will typically
have control systems significantly more complex than those found on shufflers or rollers,
involving multiple actuators, servos, or valves running through a specific sequence to
produce motion.

Shufflers and novel non-wheeled robots may weigh up to 50% more than their standard
class weight limit. (Option: Shufflers and novel non-wheeled robots receive no weight
bonus)

If a robot is supported and/or propelled by parts that do not normally undergo continuous
unrestrained rotation around a horizontal axis, but uses a system of mechanical devices
such as cams or crankshafts to generate reciprocating motion of those parts from one or
more continuously rotating drive shafts, it will be considered a shuffler. The defining feature
of a shuffler (versus a walker) will be the ability to generate continual forward motion of the
robot from continual rotation of its drive motors. Shufflers typically have electrical control
systems indistinguishable from those on wheeled robots.

Any other form of locomotion that is not contained within wheeled, walking, or shuffling is
considered a novel non-wheeled form of locomotion. If you are intending on building a robot
that may fall under this classification contact the event(s) that you plan on attending with the
robot to confirm what they will classify the drive system as and what, if any weight bonus
will be allowed.