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Drogerdy - Raspberry Pi Controlled Tank Bot

by timmiclark, published

Drogerdy - Raspberry Pi Controlled Tank Bot by timmiclark Jan 26, 2015
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29219Views 4830Downloads Found in Robotics
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Summary

The second prototype out of the jRobot project, this little tank bot makes use of a number of simple parts to do a whole lot.

I have updated it to make it more versatile. The tracks are a little more grippy as well!

https://www.youtube.com/watch?v=MJIx0cyOL3s&feature=youtu.be

The jRobot project allows my students to dock their Raspberry Pi with any of the robots, plug it all in and program away.

The sample build shown makes use of the MCP3008 ADC to allow the RPi to access a range of analogue sensors including the Sharp 2Y0A02 Infrared distance sensor.

It has the same pin based docking system as the Apogee Robot (http://www.thingiverse.com/thing:648394)

Instructions

Demo Video: https://www.youtube.com/watch?v=MJIx0cyOL3s&feature=youtu.be

You'll need 26 tracks per side. The tracks are joined by 35mm long 2mm stainless steel pins. (The same pins are used to hold the RPi in place.

Each track assembly will need: 2 x Cogs; 2 x Inner Cog Brackets; 2 x Outer Cog Brackets; and 1 x Track Mid Frame (I am yet to test the improved inner frame)

The two track assemblies are then joined by 2 x body parts. The motors must be installed before the body parts are glued together.

I glue the whole thing together using 5 minute epoxy. Some one a tip of each stainless steel rod is also helpful to stop the tracks from falling apart.

The motors fit the cogs directly and are no-name yellow geared ones that you get on eBay (http://www.ebay.com.au/itm/1pcs-Anti-interference-f-Robot-Smart-Car-Chassis-DIY-DC3V-6V-DC-Geared-Motor-TT-/291314517942?pt=AU_B_I_Electrical_Test_Equipment&hash=item43d3b2c7b6)

The motor contoller in the same bot is an L298N board which fits perfectly in the bottom of the tank body. ( http://www.ebay.com.au/itm/1pcs-Anti-interference-f-Robot-Smart-Car-Chassis-DIY-DC3V-6V-DC-Geared-Motor-TT-/291314517942?pt=AU_B_I_Electrical_Test_Equipment&hash=item43d3b2c7b6

Their are 4 x 5mm holes for LEDs and a square hole that allows for a sensor bracket and cable access.

I use a Step Down Buck power regulator that has a USB output to power the Pi - while the motors run straight of the battery. This does mean that the Pi will restart when the batteries run low. I use 2 x 9V rechargbles (500mAh each) which allows for a good 30+ minutes of run time.

I use an Adafruit perma proto quarter size breaboard for the breakout board and use header pins so that my students can use jumper cables to wire it up.

The sensors are up to you, but I am using two sharp infrared sensors on the one shown that run through an MCP3008 ADC and interface with the RPi via the SPI bus. I also have a light sensitive resistor on it and plan to add a sensor at the rear and one facing down to stop the robot driving off cliffs.

I have plans to be able to extend the length of the track assembly adding a third cog ... but I need to overcome some derailing issues.

Believe it or not, the one shown was printed on an Up! Mini as I did not have access to my school's larger printer over the summer break.

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Great tank! How do all the bits hold together? I'm assuming some of the parts are glued/welded as I'm using ABS and acetone.

Yes - glue - I have used super glue - I have also used the Dremel "welding" technique.

Hmmm ... hard to tell if they are 2mm or 2.2mm - if they are 2mm they will work well.

A different idea which has worked as well is to stick some 1.75mm filament off-cuts in and then melt them in hard at one end with a quick jab from a soldering iron. This has worked for me on one tank.

Hello sorry for the inconvenience but what kind of glue used for these parts ?

I have mostly used two part epoxy glue. For some parts (like holding the LEDs into their holes) I use super glue.

I'm having some problems. I used 1.75 filament pieces to assemble the tracks. The tracks are a tight fit to the cogs (no sag).When I run the motor it locks after a while because the cog indentation misses the track pin. I think my track ended up with a longer (or smaller) distance between the segments. I tried to make the track one segment longer and then it is is very loose but the problem persists. Is there a way to increase the tolerance or fix the track?

I'm thinking about printing a cog that has thinner teeth or no teeth at all. Would that help?

Sep 23, 2015 - Modified Sep 23, 2015
timmiclark - in reply to flima

Sorry to hear you are having problems. I have problems with some filaments and not others and more often on my Flashforge than I do on my Up! Mini.

There does need to be a bit of a sag (about 10mm) for the tracks for it to work properly on this model.

The length of the tracks is important and need to be consistent. The way I have dealt with this problem is to change the diameter of the hole that the pin goes through (the middle one). On one track assembly I will use a number of different sized holes.

If you look at the Prototank ---> here http://www.thingiverse.com/thing:972768 --- you will see that I have included a number of different sizes (you can tell by the file name)

ProtoTank
Oct 3, 2015 - Modified Oct 3, 2015
roboknave - in reply to timmiclark

I was curious if you had tried chamfering the cog edges just a tad. Not TOO much, as you of course want plenty of cog. My track is exactly as you describe, with the 10mm sag (maybe slightly more, but not much) and what appears to happen is that things work fine for a while, but then for a reason I can't quite see, the tread doesn't fall nicely into the cog. I chamfered one side of the cog (with a knife, because I didn't want to reprint it just yet) and it helped keep this from happening quite so much. It also helped alleviate some of the sprue issues I was having (I would get some on a few of the treads on the inside). Anyway, I love the design. I'm actually going to stick my beagle bone black in there. I have an old JStamp (If I can develop for it again) I might revive and stick in here as well. Anyway, really cool, and simple. I used panelling nails for the treads. Might be easier than cutting up hangars (unless you've got a closet full of them!) I don't know if you have access to those as easily as hangars. The first set of treads I printed had some of the holes a little off, so the nails actually did need to be hammered gently, but if the treading is printed correctly (I used the one straight from the track.stl) things work really well. Thanks again. I'm looking forward to getting this thing going.

Yes, chamfering the edges might work.

In my next rework of the cogs, I intend to make the cogs more like actual cogs and not just circles cut out of circles.

I need to do this as the circle idea does not work when I scale up to say a 100mm cog radius.

Planning to make a 1m high "protocol droid" in the fashion of "Johnny 5" or Wall-e.

Oct 4, 2015 - Modified Oct 4, 2015
roboknave - in reply to timmiclark

I saw something like what you are talking about that might work here. Maybe if the teeth were rounded it wouldn't catch. I think that is kind of what happens. Since the treads are printed, the .2mm print I used produced the expected striated finish. I think at some point this tends to grip the teeth of the cog, not letting the round middle part slide nicely in and out of the grooved area in the cog. That seems to be the real major binding issue. If it weren't for that, I think this design works pretty well. I've seen others, some really similar to this, but with the rounded cog design. When I go to do this again (and I'm eventually hoping to print another one, but one thing at a time), I think I'll look into rounding the cogs. I did file down the sides and one side of the teeth just a hair, and it does help, but I still eventually get stuck and the tread binds. The bind isn't quite as strong as it was, so maybe the motor can take care of it. When they get here. Last I saw, they were headed for JFK... So hopefully soon.

I would have printed your three sprocket design (that is what these are, not really cogs, I just always liked "Cogswell Cogs" from the Jetsons), but my print bed is too small. 80x80x80 (or 80x75x90 in my case) doesn't always cover it. I see the value in 150x150 and even bigger.

Hello Again.

I have already printed a lot of track pieces. I managed do create a cog in open scad that should fit my tracks. Just for comparison, what is the linear distance for the teeth on the cog you created?

Thanks

Sorry I have taken so long to get back.

The formula is 50 * PI / 12 = 13.09 mm <- so the distance between the front pin hole and the rear pin hole (centre) is 13.09 mm

This comment has been deleted.
Sep 5, 2015 - Modified Sep 6, 2015

Hi,
Does it use four motors? I'm trying to fit the two opposite CogBracketInner parts with the motors assembled already but they don't fit together. Motors seem to be too long.

No - this one does not use four motors - only two.

Thanks, went with your new prototank. Awesome models, thanks for sharing.

Thanks for the response! I was able to use 4d 1 1/2 nails that worked perfectly. Unfortunately, I am struggling getting it moving. I am using 2 6v geared motors (the TT kind) and dont seem to have enough power to actually get the tracks to move. Do you have any advice there the cogs spin great without the track, but with the track the motors just cant get it to move.

Yeah .... you should be able to hand spin the tracks freely (without motors) and they should continue to move after you push them hard for a short time. If you suspend the track assembly in mid air, the tracks on the underside should sag down about 10mm (just under 1/2 inch).

To achieve this each track should pivot freely around the pin and it occasionally helps to make a few of the pin holes (mid section) slightly larger.

I also have a 2mm drill bit that I stick in and spin around each hole just to ensure that they are clean of debris.

Where did you acquire the 35mm Pins that are 2mm in diameter, I am having a hard time finding pins in that size.

I'm using metal coat hangers. They fit perfectly

I find them on ebay .... sometimes I have to order slightly smaller ones. (25 mm also works) Or I have also bought 2mm rod from a hobby shop and cut it down.

I have also been experimenting with the idea of cutting down bamboo skewers, but you have to change the diameter of the holes to match (different packets are different diameter) and spend a bit of time sanding to get the right.

What do you use as the holder for the PI? Is the file on thingiverse?

I don't have one specifically for this bot because it is the base for whatever I need.

I made one and put it here http://www.thingiverse.com/thing:824979 specifically to hold a power converter that I used a lot along with a commonly available motor shield. But this is for an A+ and not the normal B+

Raspberry Pi Camera part for Drogerdy Tank Bot

Hi, great little tank.
Is it possible to share the sourcefiles on thingiverse? I would like to use other motors and change some other small details without rebuild the whole project.

Hi I guess you must be in Australia as the motor you specify does not ship to the UK nor Austria.
And the link to the L298 board is the same as the motor.
What would it cost to send a kit of the motors and the L298 boards to Austria?

Check Aliexpress.com, found some there...

Oct 4, 2015 - Modified Oct 4, 2015
roboknave - in reply to ipblythe

I found the same motors on banggood.com (in case anyone else finds this thread and runs into the same shipping issue) ... Its a Chinese version of Amazon or something like that. But they shipped them to the US as the same link wouldn't ship to the US either. Strange, since the motors probably originated in China. Will let you know as soon as they come in if there are any defects. I ended up buying 12 for around $20 US. ($1.xx shipping).

The L298 boards are easy enough to find on Ebay UK - see for, for example: http://www.ebay.co.uk/itm/Dual-H-Bridge-L298N-DC-Stepper-Motor-Driver-Controller-Board-4-Arduino-x1-x3-x5-/181768536409

Still looking for a suitable motor though

Sorry .... I have no idea .... I would keep looking on eBay till you find one that does. I use the Chinese sellers that have free postage because it is cheaper (still can take six weeks to get here) - we have a lot of boats going between here and China.

There are a few Australian re-sellers that buy these things in bulk and then sell internationally (for this very reason) but they are irregular in their stock and their mark-up is massive.

If you are really desperate I could list some on eBay for you and send the link, but I don't have many spares at the moment.

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