RC car or tank type platform for building a robot

My 12 year old is enrolled in science olympiad competition. He has to make a robot that will pick up a tennis ball and move it somewhere
else.
It is limited to 30cm in any dimension, so RC tanks would be too big.
I thought that we could buy a 8 channel RC mobile platform and use a couple of channels to add a lifting and grabbing component.
My question is where can I purchase such a platform, there has some be some place that sells them, but nothing comes up.
I would really like to find something that runs a lot slower than a typical RC car.
thanks
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On 11/16/2013 8:45 PM, Ignoramus26083 wrote:

This would do the job:
<
http://www.youtube.com/watch?v=blvJGZAi-ig

Move fast to get it!
<http://www.ebay.com/itm/Radio-Control-Z-707-Iron-Claw-Tank-Radio-Shack-Vintage-Toy-Works-in-Box-Gift-/111214974650?pt=Radio_Control_Vehicles&hash=item19e4edd6ba
Oops, too long, about 15". Maybe you could remount the Claw. I have one that I haven't played with for 20 years and it was definitely slow.
David
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Size is the problem. If not for the size, I could easily buy an RC tank, rip off the turret and add a claw. The problem is that all RC tanks are too big. I believe that they are all made in China at one factory and are all essentially the same tank, with different shells that are put on for various retailers.
i
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On Sat, 16 Nov 2013 21:26:43 -0600, Ignoramus26083

Why not build your own platform, Iggy? Buy tracks and remove some links to scale it down for your size requirements. Use steppers to run them slower or gear them down. Use your CNC mill to make aluminum parts from (da ta ta daaaaah!) Billet Aluminum! Have your son program it with your instruction. This is a perfect opportunity to get him involved in your business.
Have fun!
P.S: Be sure to show pics of what you guys come up with.
--
We are always the same age inside.
-- Gertrude Stein
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On 11/16/2013 9:26 PM, Ignoramus26083 wrote:

W/o the claw, the base is about 9", about 23cm. Like I said, remount the claw to bring the total length to under 30cm.
David
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Could you strip the components from an RC tank and assemble your own chassis from thin plywood, aluminum extrusions and press-in bushings, with a raised idler to shorten the footprint of the track?
You'd have a stronger mounting base for the claw and the freedom to redistribute the mass to counterbalance it. jsw
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On Sat, 16 Nov 2013 20:45:06 -0600, Ignoramus26083

Maybe you could use a pair of odd frequencied 4-way controllers. One for movement of the vehicle and the other for the pickup arm/grabber. Wait, I just googledit. "radio control modules 8-channel" has lots of hits.

Just gear it down, Ig. Zimple.
--
We are always the same age inside.
-- Gertrude Stein
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"Ignoramus26083" wrote in message

Here's a couple of places:
http://www.hometrainingtools.com/robot-kits/c/33/
http://www.kitsusa.net/phpstore/index.php
RogerN
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On 11/16/2013 8:45 PM, Ignoramus26083 wrote:

I've been building exactly that, Ig.
Little robots for the older grandkids. I have three wheeled units them in various stages of assembly, and one on tracks.
I don't have any pics up yet, but I can direct you to parts sources. If your email address is valid, I'd be happy to send info. Drawings, schematics, code, etc.
I used a small aluminum plate for the base, geared dual motor unit for motion, a 1" dia "trackball" type nose roller, and a Propeller P8x32 processor (Quickstart board) for the brain.
QuickStart Board: http://www.parallax.com/product/40000
MY code is all written in Spin, but the drivers (objects) from the Parallax Object Exchange are a combination of Spin and Assembly.
Most of my parts came from Pololu (I can't pronounce it either) and they have quite a range of robot kits. http://www.pololu.com/category/2/robot-kits
Remote control via universal TV remote control unit. Cheap and easy. IR remote sensor/decoder: http://learn.adafruit.com/ir-sensor http://home.earthlink.net/~henryarnold/page22.html
The interface circuit board is 5" diameter circle, but could be shaped any way you wanted. http://www.pololu.com/category/32/prototyping-pcbs http://www.pololu.com/product/330
My "Q-Bug" robots claim to fame is that they are not supposed to fall off of the table. The "floor sensors" detect if it is safe to move.
Floor sensors: http://www.pololu.com/product/1132
Dual Motor Drive unit: (a bear to assemble!) http://www.pololu.com/product/114
Dual motor controller board: http://www.pololu.com/product/713
Wheels: http://www.pololu.com/category/24/wheels-tracks-and-ball-casters
Plastic Chassis: http://www.pololu.com/category/26/chassis
No servos are used so far, but I may add a Ping sensor (ultrasonic range finder) and use a very small servo to move it back and forth for scanning the area. But at the moment that looks more like a complication than a feature. The floor sensors are working fine, and that's all I wanted to do.
I'll post some pics. See what you think.
Richard
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Here ya go, Iggy. Just a few pics, but you can see what I'm up to.
http://www.home.earthlink.net/~cave-1/
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On Sat, 16 Nov 2013 23:54:10 -0600, Richard wrote:

Those robots all look interesting. For future robots, also consider using 18650 type batteries instead of AA's. Two 18650 Li ion batteries take up slightly more room (about 34 cc for 2 ea 18 mm x 65 mm batteries) than four NiMH AA's (about 31 cc for 4 ea 14 mm x 50 mm batteries) but weigh less (ca 68 g vs 88 g) and and pack 50% more power (2 x 3.7 V x 2.5 Ah = 18.5 Wh, vs 4 x 1.2 V x 2.5 Ah = 12 Wh) and in simplest form cost half as much per set. (I think some versions have low voltage shutdown protection and cost more.)
--
jiw

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The necessary charging and discharging protection circuits aren't that easy to design or test unless you have experience with battery power circuits. Lithiums are great if you can buy the controller, otherwise sealed lead-acids may be the easiest for non-EEs.
http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries
NiCad and NiMH are harder to charge properly, but easy to find an inexpensive charger for.
jsw
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On 11/18/2013 11:19 PM, James Waldby wrote:

Possibly. But charging issues would be more involved, and these are meant for kids...
More important to Iggy's request would be something that could pick up a tennis ball...
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On Tue, 19 Nov 2013 16:33:12 -0600, Richard wrote:

Inexpensive 1-cell and 2-cell Li ion chargers are as easy to use for 18650 cells as NiMH chargers are for AA cells. See eg <http://www.ebay.com/sch/Battery-Chargers-/48618/i.html?_nkw 650+battery+charger&_frs=1> (or click the "18650 battery charger" link at <http://www.ebay.com/sch/Battery-Chargers-/48618/i.html?_dcatH618 )
If the cells are made up into a battery pack, then yes, more issues might arise. For simple robot apps, using 2 cells in series is fairly straightforward.
--
jiw

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"Ignoramus26083" wrote in message

I don't remember if I sent this link or not, but here's a tracked chassis kit.
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXGZ87&P=7
RogerN
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On 11/17/2013 6:51 AM, RogerN wrote:

Yep. That's the Tamiya track chassis. It's the same one I used for my project.
Downside - it only has a single motor gearbox, so as built it can not turn.
You have to replace that with a double motor gearbox to be able to tuen it.
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"Richard" wrote in message

I have a boe-bot, it uses R/C servos that have been modified for continuous rotation for the wheel drive motors. Do you think the Tamiya tracked chassis would be easily adaptable to R/C servos? If not, it might be interesting to take the electronics out of a servo and connect to the double motor gearbox. The first servo's I worked on had wires going to the motor and pot, I reversed them myself, seems the newer stuff has the board soldered right on the motor.
RogerN
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On 11/17/2013 6:33 PM, RogerN wrote:

Not the track chassis. I doubt those wheels could be adapted to servos all that easily. It _could_ be done, of course, but ... The wheels are special two-piece things with a gap in the center for the web on the back of the track. They ride on a solid axle - about 3/32" I think. All but the drive wheels are free-wheelers.
There is quite a bit of tension on the the wheels because of the tracks. The tracks themselves are made up from short pieces. Right out of the box they were so tight that it looked like they were going to come apart at the connections. I moved the front axle back about 3/16" to take some of that out.
RC servos would be attractive because of the simplicity of hooking up the electronics. All the "software" is in the transmitter and receiver.
Plain motors, on the other hand, need transistors for control. That means something to run the transistors... software for on/off. PWM to control speed.
I think I've got him running though. Check the web page I scraped together last night about this.
http://www.home.earthlink.net/~cave-1/
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On 11/16/2013 8:45 PM, Ignoramus26083 wrote:

...

I don't know now, but when my kids were doing such there were groundrules on which pieces from which were to start. Not in this competition???
--


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