CamJam EduKit #3 Robot Chassis for the Raspberry Pi
by DanielBull, published
This is a 3D printable robot chassis designed to be used with the awesome CamJam Edukit #3 and ANY Raspberry Pi (all models supported).
The CamJam Edukit #3 is a kit of parts which when used in conjunction with a Raspberry Pi provide all the electronics and mechanics required to construct a programmable wheeled robot with distance sensing and line following capabilities (only a chassis such as this one is required).
Aimed at being a low cost educational tool for teaching robotics and programming, the EduKit 3 has a full suite of worksheets and is great value for hobbyists and educators alike.
For more information please check:
UPDATE 2015-11-08 Support for old Pi's
Added tray for older model A or B
Added tighter breadboard clamp
Improvements to instructions
UPDATE 2015-11-29: Powering the Pi
I've had a few people ask about powering the Pi; I was going to make a blank area for USB power packs but because they come in all shapes and sizes and it would have made the chassis too large for most people to print I decided against it.
However all is not lost, there are a number of options...
Like I mentioned above, by far the easiest thing to do is get a small USB power pack and mount it down one side using double sided tape or blue tack. I found some of the long thin narrow packs work well (see photos above, near the end)
The second option is to get a 2 cell LiPo battery (7.4v) and a buck converter to step it down to 5v. In the photos above I have included an example using a Ryanteck DC - DC stepdown ( https://ryanteck.uk/power/16-dc-to-dc-stepdown-regulator-with-4aa-battery-box-0635648607214.html ). If you use this method you will need to monitor the battery voltage to make sure it doesn't get too low otherwise this will damage the battery, I'm using one of those small low cost integrated LED volt meters.
- The third option is to get a single cell LiPo battery (3.7v) and a boost converter to step it up to 5v. In the photos above I have included an example using an Adafruit Power Boost 500C ( http://makersify.com/products/adafruit-powerboost-500-charger-rechargeable-5v-lipo-usb-boost-500ma ). This is particularly useful as it also stops it getting too flat and charges the LiPo when you connect power your normal Pi power pack its microUSB.
UPDATE 2015-11-29: Larger wheel holes
We've had a report that some people are getting fouling between the axles/shafts on the wheels and the holes in the chassis.To solve this I have added a new version of the chassis with 14mm holes instead of the normal 13mm.
UPDATE 2015-11-29: Pi Zero tray!
Its finally here, the Pi Zero tray, using a Pi Zero will give you LOADS more space for all your extras :)
UPDATE 2015-12-04: Updated Pi Zero tray
Added missing SD card slot in the Pi Zero tray.
Infill: 15% or more
Notes:This chassis is designed to be printed in PLA, the shrinkage associated with other materials such as ABS may cause the components not to fit. I personally printed this with the following settings however you can adjust as appropriate for your printer: 0.4mm nozzle 0.25mm layer height 1 loop 1mm walls (for strength) 17% infill The only thing I would strongly recommend is you DO NOT use supports as they are not required and they will clog up the holes for the wires and the slots for the trays.
Please follow these instructions carefully as getting components in the wrong way round will be difficult to correct!
(There are a sequence of photos available above to guide you with these steps)
Print the chassis (this will take some time) and inspect for issues.
Start the print for breadboard clamp and the appropriate Pi tray for your Pi. The options are:
Pi_a_plus_tray.stl - Model A+ only
Pi2_b_plus_tray.stl - Model B+ or Pi 2
Pi_a_b_tray.stl - Older Model A or Model B
breadboard_clamp.stl - Standard breadboard clamp
breadboard_clamp_tighter.stl - Tighter breadboard clamp
Turn your chassis upside down so that the side which says STICK is facing you.
Do not insert any of the components at this time but familiarise yourself with the layout. The big opening in the middle at the rear of the chassis (where the STICK writing is) is for the battery box, the two long ones either side are for the motors. The large circular shaped recess at the very front is for the bearing and the long funny shaped one between the bearing cut-out and the battery box void is for the line sensor.
On the sides of the motor bays near the back are 4 clips which hold the motor in place. If you look carefully you will see there are fine slots at the sides of each clips, use a craft knife to make sure these are clear so the clips are able to flex slightly.
Take one of the motors and feed the two wires through the hole in the motor void from the bottom to the top of the chassis.
Hold the motor so the yellow gearbox end is at the rear of the chassis (the little yellow tag on the back will poke out) and the wires come out the same side of the motor that the hole is on (its important that the wires should not cross over from one side to the other). Then feed any slack in the wires though and with the chassis resting partially on a bench carefully snap the motor in place being sure not to pinch the wires.
Repeat for the other motor
Inside the battery box opening in the chassis there are two holes which go all the way through, the smaller one is for the wires and the bigger square one (with the on/off writing on the top of the chassis) is so you can access the switch from the top. Feed the battery box wires through the wire hole from the bottom to the top of the chassis.
With the battery box aligned so that the "open" writing is facing you and the on/off switch on the box lines up with the on/off hole on the chassis; insert the end of the battery box with the wires in its place first being sure that the wires are not trapped (pull them through the hole as you do it).
Finally snap the opposite end (marked open) of the battery box in place. If you have done it correctly you should now be able to switch the box and and off from the top of the chassis and easily slide on and off the battery cover without having to remove the battery box from the chassis.
If your battery box is loose; remove it again and affix the double sided sticky tape provided in the EduKit in the cut-out marked STICK and repeat the step above.
Inspect and clean out any swarf from the two screw holes in the ball-bearing holder recess at the front of the chassis.
Pop the ball bearing out of its holder (by sticking your finger through the hole in the back) and insert the holder in the bottom of the chassis so the two screw holes line up with the screw holes in the chassis (you may need to trim the middle plastic post back very slightly if the bearing holder is too tight to get it on).
Its likely that the bearing holder wont stay in place well enough on its own, so get the two small bolts from the EduKit (you don't need the nuts) and with the chassis face down on a solid surface, screw down the bearing holder being sure to select the correct screwdriver and push reasonably hard because you will be cutting a thread in the plastic and the small bolts are easy to damage if the screwdriver slips.
Re-insert the ball bearing in the holder and ensure it spins freely.
On the top side of the chassis, use a small craft knife to trim any excess plastic from around the edges of the slot surrounding the PiWars robot which you will be using for your Pi tray and also clean any excess from around the base of the Pi tray.
Orient the Pi tray so the large recess in the tray for the GPIO is facing the front (bearing end) of the robot and the smaller recesses for the HDMI and power are facing the rear (battery end) of the robot. Insert the tray in the slot, the fit should be quite tight and take some force, be careful not to damage your Pi tray or you may have to reprint it. If you really can't get it in, try very very slightly widening the slot with a craft knife and/or gently sanding the sizes of the Pi tray. If you find it too loose a small piece of paper in between the edges and the slot will tighten it up as you push it in.
Remove any excess plastic from the square slot which surrounds the PiWars text at the front of the robot in much the same way you did for the Pi tray. This will be for the breadboard clamp.
Place the breadboard on the PiWars text and the clip the clamp over the top of breadboard and into the chassis to hold it down. Again if its too tight you can widen the slot with a craft knife and/or sand the edges of the clamp, and in addition there's also a tighter version of the clamp. As an alternative you can stick the breadboard down using by peeling off the sticky back instead of using the clamp.
Insert your SD card into your Pi then insert the Pi into the tray by pushing it down firmly near the edges. If you ever need to remove the tray be sure to remove the Pi first. If you need to remove the Pi eject the SD card and gently prise it out with your finger at the SD card end, be careful not to damage the Pi.
With the battery box switched off place your EduKit GPIO board on the Pi and connect up the motors as shown in the CamJam worksheets and test.
Once you are happy that your motors work, feed one of the line follower jumper wires (socket end first) through the remaining hole on the top of the chassis (between the breadboard and the Pi) through to the bottom. Connect it to the line follower and the Pi as show in the EduKit worksheet.
Repeat for the other 3 wires.
Before fixing the line follower in place first test it using the EduKit worksheet demo programs to make sure your wiring is right. Once all is good label your wires at the Pi end.
Next feed through the wires so there is no slack on the bottom side and carefully snap your fully connected up line follower in place over the stud on the bottom of the chassis (the wires should be at the back of the chassis and the LED sensor at the front). If the stud is too tight to get the line follower on - very gently squeeze the stud with a pair of pliers to make it smaller. If it's too loose, with the line follower in place, use a soldering iron to spread the plastic out slightly to hold it in place.
Finally insert your wheels onto the motors as far as you can (be sure to line up the slot), then pull them out slightly so they do not foul with the chassis and away you go!
If you wish to use the ultrasound sensor insert this in the very front middle of breadboard pointing forwards like eyes. You should be able to push it in far enough that the breadboard clamp supports the ultrasound board and keeps it pointing forwards.
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CamJam EduKit #3 Robot Chassis for the Raspberry Pi by DanielBull is licensed under the GNU - GPL license.
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