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autoCut

robot lawn mower on steroids

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autoCut is an automatic lawn mower. The goals are:
- Fully automatic operation
- Battery changing station instead of charging
- Long term: Do not drive through the garden in a random manner but with a plan

- Four weel drive with kink steering
- Electric mowing height leveling
- Two 85 watt mowing motors, each equipped with two very sharp blades, able to snap back on hard obstacles
- On the fly interchangeable LiPo-battery with voltage monitoring, about 1 hour of battery live on active mowing
- Wifi network connection for web interface which includes gamepad/joystick remote control
- Modular electronics: a cuple of modules, connected with a power- and I²C-bus with a Raspberry Pi as master

System design of the robot itself:

Overview of the whole system:

  • 1 × Raspberry Pi B (first version) Running Arch Linux; soon to be replaced due to I2C issues (hardware related)
  • 1 × TP-Link USB Wifi dongle with wide range antenna
  • 1 × Power supply module provides UBat, 5V; Battery voltage monitoring, 5V fallback system, fuses
  • 1 × Driving module 4 H-Bridges, Back-EMF speed measurement; hinge angle measurement, automatic drive regulation
  • 1 × Mowing module 2 H-Bridges + ADC for electronic mowing heigt setting, 4 FET driven PWM channels with Back-EMF for mowing motors
  • 2 × 14.8V 5Ah rechargeable LiPo batteries Main power supply
  • 2 × 5V USB power bank Fallback for the system to run even if main batteries disconnected (change batteries)
  • 4 × 6-24VDC geared motors for driving (CHM-2435-1)
  • 2 × 12VDC mowing motors (CHM-2435-1)
  • 1 × 12VDC geared motor for setting mowing height http://www.pollin.de/shop/dt/MjM1OTg2OTk-/Motoren/DC_Getriebemotoren/DC_Getriebemotor_mit_Spindel_200680_12_V_rechts.html

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  • smoking robot out of control

    schuhumi08/08/2015 at 18:31 0 comments

    "Angstwiderstand" (literally "fear resistor") is a German expression for resistors you put in your design that do nothing in normal operation. Here's why you should put them in there anyways:

    Today I had a few problems with the h-bridge controlling the height adjustment. Later I foolishly left the robot unsupervised in the garage with the high power circuitry on to let the usb power banks charge. After some time the l298 h-bridge went nuts:

    Now that's toast. On the high power side the l298 is connected to the 14.8V power rail (+BATT), the input pins are connected to the microcontroller:

    It seems like while bursting in smoke the l298 shorted +BATT to the micro, which destroyed it. Have a look at that bulge:

    As you can see in the schematic the micro also controlls 4 FETs, two of which power the mowing motors.

    As a result I had a smoking robot running it's mowing blades at full speed despite all controllers powered down

    When I discovered that scene gaining control again luckily was as simple as flipping the switch for the high power circuit. Things learned from this:

    • Put current limiting resistors in datalines (Angstwiderstand) to protect components from each other in case one blows up. In this case 1k resistors in all connections between l298 and microcontroller could have prevented this scenario
    • Don't leave weird contraptions unattended with only a mosfet preventing them from becoming hazardous

  • Snow Shield & Refurbishing Drive System

    schuhumi12/30/2014 at 22:43 0 comments

    Well, it has been some time since the last update.. - but with vacation now there's stuff happening:

    As you can see the casing on the back made some progress and there's a snow shield now!

    I assure you it does work reasonably well, but I missed to shot a video and took it apart shortly after. The reason is that now the drive system has to do some heavy work and it revealed some issues:

    • The mounting of the wheels to the motors is not sufficient for snow plowing
    • The drive system supports two modes: a) regulate torque: measure a torque-ish value from the front wheels, do some calculus and apply it to the back whells b) regulate speed: the speed for all wheels is regulated individually, this isn't ideal for flat surfaces (more motors than there are degrees of freedom -> slightly tearing tires due to inaccuracies) but very nice for snow. Problem: b) doesn't seem to work as nice as it once did, not sure why though. I suspect the BackEMF-speed-measurement to have some trouble

    Countermeasures:

    this is the new mounting system for the wheels. Yes, I drilled wrong :-D No problem though.. Thanks to the screws there is no slipping no more and the axis is quite straight as well.

    Another problem with the motors was that the connections between gearbox and motor itself were loose in all cases and therefore the whole assembly was rather noisy. To solve that I opened the boxes. Sadly they're not meant to be opened so you have to drill-open them (6-7mm drill, go down ~2mm in each corner). This is what you're greeted with:

    Cleaned of the nasty grease (<- honestly the most work) and disassembled:

    The motors are mounted with (slightly oversized) retainer rings, originally only loctite was used.

    And here's the clue regarding the speed measurement:

    BackEMF is going to be supported by photoelectric sensors, hence the two holes in the gear. Why not replace BackEMF completely? Well, these are the numbers of teeth of all the gears:

    • Motor: 9
    • Small gear: 9, 41
    • Middle gear: 13, 58
    • Big gear: 67

    Therefore the number degrees per either rising or falling edge from the photoelectric sensor are:

    0.5 * 9/58 * 13/67 * 360° = 5.4°

    With the 14cm wheels that's a distance of :

    0.5 * 9/58 * 13/67 * 2 * Pi * 70mm = 6.6mm

    And I'm pretty certain that that's not enough for proper regulation on very low velocity. Now I could drill more holes into the gear, but those are so damn rock solid I ruined all my 3mm HSS-G drill bits with the 4*2 holes already - so no, won't do that..

    For the sensors itself I ordered 3mm (like LEDs) phototransistors which get inserted in a 3mm hole on one side of the gear and a 3mm LED on the other.

    In case you're interested the the motors: CHM-2435-1 is their model number and they're quite cheap. Got mine for 9€ each on http://www.pollin.de/shop/dt/Nzc1OTg2OTk-/Motoren/DC_Getriebemotoren/Gleichstrom_Getriebemotor_CHM_2435_1.html

    And here's another minor thing I added to height adjustment mechanism:

    Before in case the connector of the height measurement would have become loose in theory the motor could have teared the assembly apart or made the circuit burst in smoke. Now it gets shut off by a limit switch and a diode allows it to drive down only

  • Testing the new mowing system

    schuhumi10/10/2014 at 21:09 0 comments

    The last few days I was busy with rebuilding the mowing system. Now there's a lot less noise and vibration. It also got the laser cut hood mounted with springs to make it flexible.

    The gain in power is just astonishing:

  • New embedded Linux computer

    schuhumi10/08/2014 at 21:22 2 comments

    No doubt that the Raspberry Pi was the Board bringing embedded Linux to hobbyists and tinkerers. In fact I was one of the very early birds purchasing one. As you might remember RS and Farnell got DDOS'ed very badly - it was an awesome feeling seeing the Rapberry gathering that much attention.

    But at the moment I'm a bit fed up with it:

    • Slow CPU
    • Very limited RAM (remember that the first version had 256mb only)
    • Power consumption is not particularly low
    • Most annoying: A terrible hardware related I²C bug which makes communication with AVRs very hard. If an AVR can't handle an I²C event immediately it uses clock stretching, but this can screw up the Raspberry's I²C-bus hardware wise.

    I checked all the boards supported by ArchLinux ARM and settled with cubieboard 2:

    Read more »

  • Ultrasonic distance measurement master <-> node

    schuhumi09/27/2014 at 18:06 5 comments

    Meanwhile I got a working master and node. The master can send a package (one byte so far) to the node, the node responds and the master calculates the distance:

    Keeping in mind that it is  calibrated rather loosely the results are very good. The distance value is very stable and +-0.5cm accuracy should be archieveable.

    What the data package looks like:

    • two start bits (both high)
    • four bits target address
    • four bits command (The master transmits 1=DoEcho and the node responds 2=EchoReply)
    • two parity bits
    • one stop bit

    I need to increase the number of parity bits, because two bits result in an easy 25% chance for the parity to be right anyways.

  • laser cut aluminium parts arrived

    schuhumi09/24/2014 at 22:31 4 comments

    Cutworks where surprisingly fast (compared to the estimated delivery date in their mail (10. oct)). Everything turned out very nicely. The hood (sorry for bad quality, phone had problems with focus):

    The the platters:

    As you can see either two or four blades per platter and variable diameter are possible. Mowing some grass:

    The new platters reduced the noise a lot, but there's still some vibration due to worn out bearings (previous designs rather unbalanced) and inaccurately modified motor shafts (previous designs needed a flattened shaft).

  • Ultrasonic data transmission - proof of concept

    schuhumi09/16/2014 at 22:03 2 comments

    One of the outstanding features of autoCut is the ultrasonic positioning system. Since no other (lawn mower) robot I heard of has this feature it's a tough one. I posted a sketch on how this could work and I set out to make a proof of concept.

    After some tinkering it works very well, here's a demo:

    This is how it works:

    The signal on top is the one fed into the ultrasonic transmitter. It is 40KHz as long as data is transmitted, and on every 1 there is a phaseshift of half a period (waves get inverted). On the oscillating receiver this causes the amplitude to drop to 0 and then start rising again. So 1es are where the amplitude is zero (blue dots) and 0 are where the amplitude remains high (red dots).

    In this case the data stream is 01100011, written in correct binary: 0b11000110 (least significant bit gets transferred first).

    The signal of the receiver gets amplified, one-way rectified and buffered by a capacitor. This creates a signal the represents the amplitude of the received signal.

    With the help of  a small phaseshift (caused by resistor+capacitor)  comparator creates a digital signal which indicates when a signal starts rising or falling. Now when the amplitude is ~0 and starts rising again, the digital signal switches from low to high. Under friendly conditions this is enough already to decode the data stream.

    To make sure that the switches from low to high are valid 1es (amplitude must be near zero) another comparator is used to create a signal representing the level of the amplitude. To receive a valid 1 the flank from low to high must occur AND the level of the amplitude must be zero. As you can see I also introduced a small XOR-checksum, which will be extended to 4 bit due to occasional false data (2 bit: 25% chance that checksum of corrupted data stream happens to be right).

    So far I'm pretty satisfied with the results. Improvements I'm working on:

    • use MAX232 as amplifier for the transmitter
    • use better receiver/transmitter capsules
    • use a better operation amplifier for the received signal (CA3140 so far which can't do rail-to-rail -> 2-3V max output on 5V power supply)
    • Get bidirectional data transmission and distance measurement working
    • work out a way to spread the sound into all directions

  • Bunch of minor updates

    schuhumi09/16/2014 at 20:30 0 comments

    Already some time ago I built this prototype of a battery pack:

    It can hold two 14.8V 5Ah LiPo batteries wired in parallel. I did some tests with one battery earlier and estimated from that this should be enough to mow at least 1.5h non stop.

    Apart from connector orientation the design is mirrored. The front face with the two connectors will sit on the robot with the left connector providing the amps and the right one reporting individual cell voltages. The connectors on the other side (facing upwards when battery pack is mounted on robot) do exactly the same. The idea is that the battery changing station can grab the pack and connect to it in one step. The changing station will be a big disk that can rotate, move up/downwards and hold up to 3 battery packs (see sketch on system design)

    The biggest problem on a mechanical point of view is how to craft the docking mechanism. The problem is that this has to be very accurate to work smoothly, but my most advanced tool is a cordless drill... Fine adjustment must be possible via screws with washers in bigger holes or something.

    This are the electronics inside the battery pack. There are two of these simple boards in one battery pack:

    As you can see rather simple, simply a bunch of connectors and solder pads to join everything in parallel and provide mounting options. The PCB is homemade via toner transfer (probably should do a video on my selfmade laminator and etching machine..)

    I also purchased the mowing plates and hood that will be laser cut from aluminium:

    As you can see blades of different sizes and two or four blades per plate can be mounted.

    All in all it's 65€ and the parts will arrive ~ 10. Oct. I purchased at http://cutworks.de/ an their website/tools are really great, will see how the parts turn out.

  • Thoughts on the ultrasonic navigation system

    schuhumi08/23/2014 at 00:34 0 comments

    As you might have read I claim the ultimate goal of the robot to be to navigate through the garden with an ultrasonic positioning system. I thought about navigation and positioning since the beginning of the build, but just recently something came up my mind that I think of as an realistic solution: sound

    Sound moves rather slow compared to the speed a microcontroller can process data, thus making precise distance measurement easy. There's a great chance you actually used one of these at some point:

    This is a HC-SR04, a cheap (~5€) ultrasonic distance sensor widely used by hobbyists. The principle is fairly simple: One of the round thingies is an ultrasonic speaker, that transmits a short ultrasonic burst into the world. Eventually this sound reaches an object and gets reflected on its surface (echo). The other round thingy listens for that echo. The delay between transmit and the receive is what the module sends to your microcontroller which can then easily calculate the distance from that.

    Now I want do take this principle one step further:

    Read more »

  • Improving the mowing system

    schuhumi08/20/2014 at 18:56 0 comments

    The mowing system turns out to be one of the toughest parts to work out. Of course the robot can't mow as fast as it's gasoline powered competitor, therefore it needs to be very silent to compensate the longer noise-frames and not annoy the neighbours. 

    I decided to ditch the bearings since exactly aligning the motors with the bearings while maintaining a connection withstanding the tremendous torque was beyond my capabilities. (note that my most advanced tool is a cordless electric screwdriver / drill ). This shouldn't be too much of a problem, since one motor of this kind costs ~2.5€ and these probably need to be replaced anyways at some time since they have brushes.

    This is how the shaft of the motors is connected at the moment:

    (I can't see the bend when looking at the real thing - not sure whether camera or eyes broken..) To minimize vibrations I'll craft these once again as precise as I can and mount laser cut mowing platters to them:

    The hood (green) will also be lasercut from aluminium. The straight sides are for mounting vertical flaps. They will not only prevent grass (and slugs..) from flying around, but also sense if the blades are about to touch the ground. Our garden (and probably most others too) has lots of little holes in it. That's not a problem with the rear wheels (front tips up a bit), but with the front wheels it occasionally happens that the blades get stuck. The design isn't finished yet, but the company that run this service are on operational vacation anyways.

    JohnsonFarms.us wrote a comment whether I considered to use a string trimmer instead of blades. I built one and tried it out

    Here's a video on that:

    ( Sorry for occasional brain overflow - either forgot how to English or to move the cam accordingly. The string trimmer is almost invisible since tiny grey surfaces move damn fast )

    In a longer test I did previously the string trimmer (had strings on both motors) turned out to use just too much energy. The RPMs need to be very high to actually cut the grass and not just bend it, which makes it noisier than the blades. The idea is great, but I'll stick to blades.

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Discussions

kevin.downe wrote 01/19/2016 at 14:51 point

BTW:  What circuit design program r u using?

Kevin

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schuhumi wrote 01/19/2016 at 23:09 point

KiCAD. It's open source and received a very huge update to stable version 4  lately (including the parts sponsored by CERN, e.g. push&shove router).

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kevin.downe wrote 01/19/2016 at 23:17 point

Thanks.  I use Eagle.   I like it a lot.

Can u help me figure out how to do serial com via ultrasound myself?   I want to use 2 arduinos talking serial data stream in Hex.  I only want one way so one has transmitter and the other has reciever.  Two way would be great but not nec.   It is a broadcast set up.   I ordered some arduino distance ultrasound sensors but I dont think that is what you used.   Prob can use them for parts.   Pls give me more info if you can.

Thanks for the quick reply.

Kevin

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kevin.downe wrote 01/19/2016 at 14:45 point

I am working on Arduino telemetry project with live lobsters.   We are measuring heart rate and internal core temperature as well as position.  I am currently using Bluetooth MESH to communicate using CSR chipset.  However, I need to be able to communicate the telemetry data in a fish tank.   Your ultrasonic com in this project is really cool.   I would be willing to hire you to help me with this if you wish.   Might help you get cash to finish your project.   Do you have the circuit and code to communicate point to point now?   It looks like it.   Pls contact me at kevin.downe@hotmail.com if you are interested.

Thanks

Kevin Downe

Innovation Controls Inc

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schuhumi wrote 01/20/2016 at 00:08 point

Just sent you a mail :)

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campbell.kb wrote 01/15/2016 at 15:38 point

Have you tested maximum incline on which it can operate? I ask because I live in Tennessee and have a STEEP front yard. Having a robot doing the hill work would be a handy (if it could handle it...).

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schuhumi wrote 01/19/2016 at 23:07 point

No, I didn't test it so far. It should do a pretty good job though. Im not able to work on the robot at the moment due to exams, but I'll have more time in march.

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Stefan-Xp wrote 12/18/2014 at 21:29 point
Are you going to add a snow shield for winter? ;)
Looks rather useful, if snow is coming ;-)
https://www.youtube.com/watch?v=9sVKLsMk0Uk&list=UUQkElNkk48mfKadXBHNpp6g

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schuhumi wrote 12/26/2014 at 12:09 point

First snow today! Thanks to christmas vacation autoCut should make some significant steps forward. Ultrasonic positioning and indeed a snow shield are the goals. With the tremendous torque available this should also work beautifully

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Stefan-Xp wrote 12/26/2014 at 20:21 point

Still looking forward for your next updates ;)

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Marcus Vinter wrote 10/30/2014 at 12:09 point
I know you are committed now but it might have been nice for you to make it drive-able while you mow the lawn once using a controller then it can record the journey and replay it back whenever you need to cut it again.

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schuhumi wrote 11/01/2014 at 21:10 point
Yeah, that's possible once the ultrasonic positioning system is working. Just replicating the input from the controller won't work because the lawn is a little different every time so after a few meters the robot would completely loose his track.
Once positioning is working I want to implement that autoCut can mow a shape into the lawn which is drawn in beforehand on the computer.
This feature will come, but sadly I'm running a little short on spare time for this project (school stuff) so it might take a bit.

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Peter McCloud wrote 10/10/2014 at 14:51 point
Great project, I'm impressed. Have you considered using the Piksi GPS? http://www.swiftnav.com/piksi.html
It could help with navigation since It's supposed to have centimeter level accuracy. The big downside is that's pricey.

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schuhumi wrote 10/10/2014 at 17:20 point
Thank you! I didn't look into Piksi in particular, but I'm familiar with the principles of differential GPS. I know how these are very pricy if done properly. And to be honest, 1k$ is far beyond what I am willing to pay for individual parts (Remember that I just did an apprenticeship and I'm now attending school again (to get permission to study at university)).
Also if I get the ultrasonic positioning to work properly it would be a cheap alternative perfect for all kinds of hobbyist projects.

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Peter McCloud wrote 10/11/2014 at 01:07 point
Hah, I knew it was pricey but I didn't think about in a price per component aspect. That'd be more expensive than anything I've got on my project, including the gas motor.
I agree, your ultrasonic positioning is a good alternative and great for other projects. I also like your new video. It looks pretty slick.

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Electronic Man wrote 10/10/2014 at 05:50 point
Hi,
For your reference you can have a look on my mower :)
https://plus.google.com/photos/112731006972393721439/albums/6068444706044602241
I do not have a picture here of the electronics but until now i have made it like the ardumower project, all with finished boards. The cut width is approx. 60cm.
I have changed the drive motor because they where to fast, and lost power at low RPM.
I am using this motor know: http://www.smolka-berlin.de/onlineshop/en/artikel/SWF_VALEO_NIDEC_ITT_404.000_gear_motor_24V_DC_Typ%3ASWMK/4280
I am following your project to get some more ideas... :)
/Kasper

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schuhumi wrote 10/11/2014 at 14:29 point
Hi :)
Very nice mower you have there!
I see you use 3 mowing motors. Do you experience any resonance effects when they run at the same speed as well? Although with the new mowing system it got better for autoCut, I'm still not completely satisfied with it...

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Electronic Man wrote 10/30/2014 at 06:51 point
Hi,
No, i have not seen that, i am still on a wood plate, and it can maybe damp some of it.... i have a problem with one of the motor is not correctly balanced and it actually takes more power and the driver goes in temp. cut off. But i think i will have some smaller motor, i think they are to heavy...

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Joshua Conway wrote 09/30/2014 at 16:38 point
Greetings, very cool project you have here!

I'm curious: have you thought of using RobotOS for your project? http://www.ros.org/
It has many computer vision libraries built in, along with easy(ish) control of motors given the focus on a robot API.

I'd be glad to give some assistance with the computer vision department.

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schuhumi wrote 10/02/2014 at 15:40 point
Thank you!

I have to admit that I didn't look into ROS very much so far.

My setup at the moment ist:
[Arch Linux + Python3] --- i²C --- 3x [AVR µC + Bare metal C]

I guess this is what you find on most (complex) robots, so ROS should be possible (?). I need to read more about ROS to see what advantages would actually come up for autoCut..

As for computer vision: At the moment I'm upgrading to cubieboard 2 with A20 dualcore processor, so there should be enough power to have some fun. Didn't put any brainstorming into this so far, but I think it could improve object detection and safety a lot. Time to purchase some wide angle webcam I guess..

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Electronic Man wrote 10/03/2014 at 07:40 point
Then still keep the AVR for time critical stuff?

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VPugliese323 wrote 10/03/2014 at 12:18 point
If you are interested in utilizing computer vision, then the following is for you.

In addition to using a single wide angle webcam, I recommend you use stereovision and make it so that the "eyes" can turn as it turns. While this will may require more processing power on your part, I feel that the benefits outweigh the costs.

On a side note, I see you are using Python. I do not know much about ROS, however OpenCV (which I use often) supports both C/C++ and Python for creating vision code. If you are comfortable in Python I suggest looking into it.

As it is a jump to add vision, I suggest you create a "version 2" of this project, tie up the loose ends in "version 1" and then start at the beginning of your design and see what improvements can be made and what needs to be upgraded to incorporate this new system. If you are clever enough in designing your vision code, you might be able to get away with running everything on a minicomputer (like the RasPi).

If you need help with vision, I know there are at least two of us that can help you (myself and the gentleman above).

All in all this is a very unique project and I look forward to seeing it evolve.

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Electronic Man wrote 09/30/2014 at 05:49 point
Hi,
Do you have any part numbers or link to the motors you use?
/Kasper

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schuhumi wrote 09/30/2014 at 16:20 point
Mowing: JOHNSON HC685LG
Setting height: http://www.pollin.de/shop/dt/MjM1OTg2OTk-/Motoren/DC_Getriebemotoren/DC_Getriebemotor_mit_Spindel_200680_12_V_rechts.html
Driving: CHM-2435-1

Note on the driving motors: I'm not sure whether I got a bad charge or if the motors are assembled careless in general. The motors aren't properly mounted on the gear box but a bit loose (also the box can't be opened). Therefore they make some noise - You might find better motors here.

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David Cook wrote 09/29/2014 at 00:32 point
Your semifinal video is accidentally set to private.

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schuhumi wrote 09/29/2014 at 00:44 point
Yeah, it was still uploading. Sorry for inconvenience caused :)

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xaveriusarian wrote 09/16/2014 at 14:12 point
can i get full spesification aand sorce code ?

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schuhumi wrote 09/16/2014 at 22:08 point
Source -> Sure! Theres this GitHub link on the left: https://github.com/schuhumi/autocut
See "Software" folder for sourcecode for all the controllers/webserver/etc

Specification -> I'm not sure what you mean by that.. In case you want schematics etc. -> same GitHub link. But most of the mechanics are crafted by staring at aluminium rods, having an idea and smashing it together. So there are barely any mechanic plans jet

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JohnsonFarms.us wrote 08/07/2014 at 03:25 point
Have you considered using a string trimmer instead of blades?

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schuhumi wrote 08/13/2014 at 00:09 point
No, but the idea is so good, that I actually tried it out. You can expect an video on that ;) (spoiler: It's to energy expensive)

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cBake wrote 08/31/2014 at 20:11 point
This. You should consider using the commercially available weed-whacker string, as they have already done all the leg-work figuring out what works well, and it is cheap and easily to find. The energy-expense aspect should be determined by the rotating mass, and the friction of the rotating assembly (given a constant grass inflow), not RPM. The key is gearing your motors down for the proper cutter RPM - figure out what a good cutting RPM is and then gear your motors to operate in their peak efficiency. See motor torque-RPM curves for more info on that.

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Adam Fabio wrote 07/28/2014 at 03:33 point
Great work schuhumi! Thanks for entering autoCut in The Hackaday Prize! A robot to mow the lawn has been the holy grail of every kid that spent an afternoon with a push mower! You're doing great so far - those mowing videos are impressive! Keep the updates coming, and make sure autCut is prepped for mowing in space!

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schuhumi wrote 08/13/2014 at 00:11 point
Thank you very much! Sorry for the gap in updates, you can expect more content soon

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J Groff wrote 07/10/2014 at 18:43 point
They have a system on some table saws that is some sort of capacitive meat detector and clutch that immediately stops the blade. I recall a dramatic demo where the guy jams a hotdog in fully spun up saw and it left nary a mark.

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Byron (odiekokee) wrote 07/14/2014 at 18:51 point
it's not exactly a clutch...it's a spongy aluminum block that gets hard jammed into the blade and stops it in 3 blade teeth passing, destroying the aluminum block, blade, and sometimes motor shaft....but still better than a finger. Seen it demonstrated in person with a finger analogue (hotdog). Rather impressive. unless you were really carried away, 3 teeth will barely draw blood.

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PointyOintment wrote 07/14/2014 at 19:22 point
It's called SawStop.

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schuhumi wrote 07/15/2014 at 00:15 point
That is a brilliant idea! I used this technique in a POV-Clock before to start and stop it. It's rather easy to implement as long as the circuit ist connected to earth, just measure the time a microcntroller neds to charge a 0V-leveled detector-pin with the internal pull-up to high-level. long time -> someone touches the pin

I will definitely do some testing on this.

(BTW: I'm rather bussy at the moment, but I'll continue on this after thursday)

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PointyOintment wrote 07/08/2014 at 01:58 point
The blades fold when they hit hard obstacles, but what happens when they hit soft obstacles (like feet)?

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schuhumi wrote 07/09/2014 at 23:50 point
As you can see in the update I'm working on a cover/bumper. But I'm still concerned about this problem, since it's quite hard to tell the difference between bare feet and thick tufts of grass. I thought about IR LEDs and how grass and skin/stones/garden hose (<- all flat surfaces) reflect the light differently. Or something capacitive (did a few experiments some time ago, worked remarkably well) since feet/garden hoses contin lots of water, but I reckon this won't work on wet grass..

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jlbrian7 wrote 07/07/2014 at 12:48 point
Looks like it should be finding landmines instead of mowing the lawn.

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schuhumi wrote 07/07/2014 at 18:17 point
luckily landmines are a rare occurrence in my garden :) In fact I didn't plan on a mowing robot from the beginning, thus the kinda strange construction. But I like how it turned out and that it is not as boring as the usual designs.

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cBake wrote 07/07/2014 at 11:27 point
how terrifying. awesome.

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schuhumi wrote 07/07/2014 at 17:46 point
glad you like it ;-)

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