This topic contains 85 replies, has 7 voices, and was last updated by 
click 1 year, 6 months ago.
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This is the first thing I’ve designed myself and printed, a 150g combat robot (antweight in the UK and Australia, fairyweight in the USA) called Plover. Both versions are printed in ABS with 40% infill and a raft (had issues with adhesion when I tried without), the red was printed without supports which worked OK but took a bit of tidying up of the mounting blocks for the lid.
- This topic was modified 1 year, 11 months ago by Steve H.
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@evilsteve If you have a glossy finish print bed, you may consider using 320 grit sandpaper to take the gloss off and get an even matte finish. This tends to solve many of the adhesion issues with the PEI bed sheet.
I operate two Betas and four Production Robox.
I am the US/Canada Technical Support engineer for the Robox.
www.hudsondesignlabs.comThanks, if I have ongoing issues I’ll try that. Everything else I’ve tried has stuck well though, and I’ve printed almost everything so far in ABS.
Really cool! 🙂
Nicely done @evilsteve, and thanks for sharing
Locksmith, software developer, Jaguar fanatic
http://www.247guardian.co.uk/Thanks guys. I’m planning to put the design up on Thingiverse once I’m happy with it.
@pelgrim - it is mad fun! The 150g ants are a good starting place too, especially if you have a 3D printer to make the chassis, the other bits can be pretty cheap depending on what/where you buy. I used to watch Battlebots/Robot Wars/Robotica when they were originally on, when Battlebots got rebooted last year my kids got into it with me and we discovered people doing it locally.
I am about to design a robot for PiWars - more like a robotics challenge than combat - for kids of our club. So far main part is big RPi in the middle. I was thinking going with 4 servos for steering 4 wheels running brushed motors with reducers but controlled by brushless controllers. It will give it a lots of mobility (rotating on the spot, moving any direction you want without turning, running like a normal car, etc…). And then go sensors - they need to be added somehow to the body…
@click - can you run it with tank-style steering? It makes for great maneuverability and power, it’s how most combat robots steer. If your motor controllers can handle the amps then you just parallel 2 off each controller, I’ve done that in a 30lb bot with great success. It’s also less mechanically complex than using servos for steering, no idea how it works with programming it though as I just use RC control and ESCs!
@evilsteve I was thinking of tank style steering but there are some issues with it. Ability to control each wheel separately will give us much more to play with.
Controlling servos (ESCs) from RPi is easy with ServoBlaster code, plus I’ve got a few of these: http://electronics.chroma.se/rpiswsb.php
BTW didn’t really sourced motors/ESCs yet. That’s the next job on my list. Any recommendation is more than welcome. Then, after that, there is designing motor mounts, base body of the robot, printing off prototypes, etc…
We should start blogging about it (there’s an requirement for it, too) so as soon as we get there I’ll post link, too…
ESCs will depend on motors which will depend on size and speed vs torque (and also wheel size).
For my 150g bots I’m using N20 style motors (10x12mm at the front) in the 300-1000rpm range. After having a brief look at the ruleset and the video on the site you linked there seems to be quite a lot of variation of the robot size and some of the bots seem to use those motors (at lower rpms) and some bigger. The Pololu motors are good quality and a good starting point - you can get cheaper clones on ebay though if cost is an issue. I suspect the Pololu 20mm motors at the 73:1 ratio would work but it depends a lot on your exact design. Do also think what wheels/tracks you want to use as that will also determine the size of the motor/output shaft.
Combat robotics usually abuses ESCs, I suspect for your application you can be less picky. All the ones I use are designed to take a signal from an RC receiver - I have no idea how you’d go interfacing them with a Rasberry Pi. Of these ESCs the Botbitz 10A ones are great in this sort of size robot - they’re Australian though and while they are available in the UK there may be other locally sourced options.
This is Telebot Rovatron 2000, which I’ve been working on… a telepresence robot based on Raspberry Pi, so I can do video chat.
Right now, power is an issue, and the motors that came with the bot platform are woefully underpowered. WebRTC seems to be the main option for the Pi-based full-screen video chat (ie. without having to initiate from a GUI), but that chews through a lot of CPU, and power accordingly. So, bolting on a more powerful motor seems overkill. I am wondering about using an RC car powertrain instead, though.
@evilsteve That’s quite a lot of useful info. Thanks Steve! I was eyeing HobbyKing cheap ESCs (~£6-7 per one) + completely clueless motors wise. Originally I was hoping I would be able to source cheap brushless motors + find gearbox for them. It seems not to be the case - there aren’t any such unfortunately. Alternative to that would be to get cheap motors with gear boxes and then rip them off and find a way to put brushless motors instead. But that lead me to - why not just get brushed motors, brushed ESC and go with it. So that will be my first prototype. Second was to try to determine RPMs I would like to go with it (hoping to win speed run in straight line) and find appropriate gear ratio - 200:1, 100:1 or less - never been sure what to go with. I’ll probably start with the advice you’ve given me here 🙂 And for wheels - I’ve, finally, got my DM head :D. I am waiting for some flexible filament to arrive and I am hoping to be able to make my own wheel with soft outside (tyres) in one go. Why not! 😀 So - I can experiment with different size of wheels if/when needed. As for power - I am thinking that as there are actually 4 motors - even if they are slightly underpowered they’ll be able to cope in short run with killing brushes with overcurrent (I do have experience with that :D). And the last thing is to decide to go with 2S or 3S LiPo battery. Probably with 2S for weight…
And last thing - driving servos/ESCs from RPi is very, very easy. Check the links I’ve posted above. As easy as following command line statement:
echo >/dev/servoblaster “4=150”
(servo number 4 to the ‘middle’)
@gid That’s really cool bot! What was the purpose of it? Drive it somewhere and then chat with the people on the other end of it? What RPi did you use? Maybe RPi2 (or RPi3) would be better now as it has far more powerful CPUs (and 4 threads?). I’ve got 4 RPi3s for the club - one to be WiFi Access Point and three for three prototypes/final robots. And battery wise - what kind of batteries did you go with? There’s a huge selection relatively cheap LiPos at HobbyKing site - and you can go with really big ones like 5000mAh easily and since they can keep 2kg helicopter in the air for 5-10 minutes I bet it can drive your robot for hours… Let me know if you need any help selecting things from there (battery/charger, etc)… Only thing with those batteries is that you don’t want to short them or puncture them anyhow! O: )
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