An antweight version of our Robotwars robot, Firestorm.
The dimensions are a little off, but overall I'm happy enough with it. My version is printed in Colorfabb XT yellow, now it just needs a sweet paint job on the back to finish it off (or I complete my Bigbox upgrade to dual nozzles).
You'll need a bunch of other parts they should be less than £50 and can be reused in other tiny robots, see below for details.
So you should be able to use pretty much any filament for most parts and any layer height between 0.1 to 0.25mm. The parts should be easy prints, there are no large overhangs, and the parts have nice large contact patches.
The lid should probably be printed in something a little flexible as it needs to be bent to fit on top, but it has a cutout so even really stiff PLA should work without snapping.
The tyres should be printed in Ninjaflex or other rubbery TPU, although you could get away with just using a couple of appropriately sized o-rings or superglue-ing some strips of rubber band instead.
You need one of each part, other than the wheels and tyres where, obviously you need 2 of each.
Bits you will need
- 180maH 2S battery
- 2 x 9g HXT900 Servos for drive
- 1 x 9g 90 degree metal gear servo
- 1 x BEC This one looks good, I'm currently using an old ESC for a 5V supply, should be much better with 6V from this supply
- Assorted heat shrink tubing
- Some 3mm cable ties
- 4 small (1/8w or less is fine, you can even use surface mount ones if your soldering skills are up to the job) 1k-10k resistors the value doesn't matter too much as long as all 4 are the same value. For better centering you can match the resistors into identical pairs
- 4 x M2 x 5mm countersunk screws (for attaching the lid, search ebay, still waiting for these myself)
- A paper clip or other thin bendable metal (for flipper hinges)
- A few cm of 1mm round elastic cord (for returning the flipper, search google/ebay etc)
- Some thick elastic bands or some o-rings 20-23mm internal diameter (if you're not printing tyres)
If you've already got some radio gear (I have an older Turnigy 9x with FrSky modules) you might be able to use that otherwise you'll need:
- 1 x Tx and Rx Seems to have mixing on board, but due to right angled plugs on the receiver, you'd probably need to solder servos and BEC directly to it to make it all fit in the shell, which might not be a problem as it is very cheap!
More expensive option:
- 1 x Tx and Rx Plugs on the receiver should be usable as they are parallel to the pcb
Even more expensive:
Buy separate micro receiver, handset and transmitter module
Modification to servos
You will need to modify the 2 drive servos for continuous rotation and, optionally, modify them for a bit more speed.
Dismantle the servo
- Remove the 4 screws on the bottom of the servo
- Pull the top and bottom covers off the body of the servo
- Cut the wires going to the potentiometer at the potentiometer end, so you have 3 free wires coming from the pcb
- Solder a resistor between each of the end wires and the center wire
- Insulate it all, I prefer heatshrink to tape as insulating tape tends to leave a mess if you need to get back into it for repairs/changes
- The PCB and new resistors will probably have to sit outside the servo with the motor wires running back through the hole where the receiver wire was running previously.
Mechanical modification (continuous rotation)
- The gears should be removed from the top of the servo
- Clip the plastic stop from under the top gear
- You may also want to carefully drill out the top gear so it freely rotates on the d shaped shaft of the potentiometer (if you don't do this the servo still has sufficient torque to turn the gear on the D shaped shaft and will do this drilling for you. If you are also doing the speed mod, you should definitely drill out the top gear as increasing the speed reduces the torque quite substantially)
Optional Mechanical modification (speed increase)
- To do this you need to remove a stage in the gear train
- The top gear on the center shaft should be removed
- Clean the oil/grease off gears of the potentiometer shaft, to make the superglue bond better
- Superglue the top and bottom gears of the potentiometer shaft, together.
- Take care to glue only the gears on the potentiometer shaft to each other and not to the potentiometer or the gear on the centre shaft
- Reassemble the gear train without the the top gear of the centre shaft.
Screw the drive servos back together
Put it all together
- You'll need to trim the mounting lugs off the flipper servo
- Put the tyres on your wheels
- Push the wheels onto the drive servos, fix with the screws supplied with the servo
- Cable tie your drive servos in place, see below
- Slide the battery in-between the drive servos with the wires exiting towards the front
- The BEC should fit on the left front of the robot, cable tie loosely in place until you've got all your wiring sorted out
- The flipper hinges are created by passing a short length (15-20mm or so) of the unfolded paper clip through the holes in the flipper and lower body, on each side, bend the ends to stop the clips coming out.
- For fitting the flipper arm, you'll need to power on the servo with the receiver so you can find the limits
- The receiver may need to be uncased and should sit just over the drive servos and battery.
- The elastic should be tied around the end of the arm (the hole in the arm is a red herring, sorry) and through the hole in the flipper. It should be fairly slack at full extension and tighter when folded away.
- Routing cables can be tricky, I found pushing spare loops into heat shrink made it easier, although you may want to cut and solder your cables to the perfect length once you've test fit everything.
Created with OpenSCAD, the lower shell is a whole load of horrid polyhedron blocks.