After 12 years as a fan, can I get a robot into the arena?

**mark_m** · 19th November 2010, 20:46

After 12 years of following fighting robots, I'm now more determined than ever to actually get a robot into the arena. I've lost count of how many I've half built and given up on.

The target this time: get one to pass safety and fight in an arena. Nothing more. Entertaining is a secondary requirement.

I've got a week off work and I'm actually going to try to build two robots: One beetleweight and one feather. They'll both be similar in design so I'm aiming to get the beetle done, see how it works out, then build the Feather.

They're both going to be fairly similar to Ewan's robot's Fractal and Flux, but without the fun of tracks. No names at the moment, I'm hoping I'll get an idea whilst I'm building them. At the moment I've got the drive train working for the feather but no idea about the frame or weapon layout. I've got a rough layout of the beetle:

Component list:
3s 1000mAh lipo from Giantcod
4 x RE280 15:1 drive motors from technobots
2 x RE280 250:1 weapon motors from technobots
tamiya wheels
sabertooth dual 5A for drive
Polulu 15A for the weapon

Has anybody got experience with those components?

CAD drawings next

**mark_m** · 20th November 2010, 15:07

Beetle CAD:

The frame/armour is polycarb (frame 8mm, armour 3mm), the scoop is 1.6mm stainless.

Still to add: removable link, power light, fasteners. What have I missed?

I was thinking about using micro deans connectors for everything, including the removable link. Anybody used micro deans?

**AbundantToast** · 21st November 2010, 10:45

Wow, Thats actually pretty darn amazing, what you going to use a drive?

P.S. I'm jelous of your cad skills ;D

**mark_m** · 22nd November 2010, 23:59

Well, its past the CAD stage! Most of the bits arrived on Sunday. I quickly put the drive and electrics together as best I could. Unfortunately I only received three drive motors but it was quite useful. Conclusions:
* Tamiya wheels are light and grippy
* Drive motors (re280/1) don't get hot
* Motors are up to it but its not very nippy on 12v, may need 4s
* ESC works well
* The receiver I was going to use is bust :-(
* 3 wheels don't work too well
* Building's fun!
Anyway, enough waffle, here's the video:

**mark_m** · 23rd November 2010, 13:25

The other drive motor appeared this morning, so I added it to the test bot. Here's a video with it with all four wheels:
http://www.youtube.com/watch?v=-9OCh4_EpBQ

I'm quite happy with the speed; its currently running on a 12V 3Ah botpack so weighs about 1.2kg. Hopefully the speed won't drop too much when I switch to a 11.1volt lithium. That should at least give me the weight for important things like a weapon and armour! I think I'll have room and weight for 4 cells but I'll wait until its finished and I know what the actually weight is before switching. Solidworks says that as modelled it weighs 1290grams, without wires, connectors or fasteners. I think wires and connectors should weigh about 30grams and the fasteners the same, so its going to be quite tight. I don't have any scales accurate enough at home to check if the components I've received weigh the same as their advertised weights. Fingers crossed!

Final picture of the bot as it is:

Hooray for duct tape! :-)

**razerdave** · 23rd November 2010, 18:34

Thats cool

My kilobot will be using the same type of motors, but on 100:1, and 11.1v lipo, so it should be fairly quick. Why are you using a massive Bot Pack like that ? I presume its just for testing

**mark_m** · 24th November 2010, 11:04

100:1? Are you using the 24V motors or the 3V ones? What size wheels are you using? If you're using the same motors as me but the 100:1 gearboxes, even with 100mm wheels you're still going to be 1/3 the speed of mine.

The botpack was just for testing. Now I've got my 11.volt lipos and a charger I'll be using those.

**mark_m** · 24th November 2010, 16:39

I intended to start cutting plastic today, but so far I've not managed it. The main set back has been finding that my stock of polycarbonate is 10mm, not 8mm as I'd designed around. The 10mm would add over 40grams to the weight and I was very worried it would make the design overweight. Attempts at lightening holes in the CAD showed that it was futile - they only saved 20grams even if I peppered it with 10mm holes :-(

I figured out a way to make it narrower though. If I mount the wheels onto the shafts the other way around then I could save 15mm off the width. That gets me 30grams back:

Left image shows the hub mounted on the deep side of the wheel with the motor shaft mounted on that side.
Right image shows the motor shaft coming in from the other side, recessing the gearbox into the wheel. I could save a bit more if I mounted the hub on the other side but I wouldn't be able to support the gearbox as easily then and actually other parts in the robot start becoming the limiting factor to its width.
After that change I realised that I could shave a bit off the length too. Just 10mm off the length saved another 30grams, so I'm now 20grams lighter than when I started and I've moved up to 10mm frame rails! Great! I just hope I can squeeze the wires and electronics in the space in the middle. Here's the latest CAD: