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

[mark_m]

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]

Re: After 12 years as a fan, can I get a robot into the aren

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]

Re: After 12 years as a fan, can I get a robot into the aren

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]

Re: After 12 years as a fan, can I get a robot into the aren

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:
http://www.youtube.com/watch?v=rwTWnwoC93c

[mark_m]

Re: After 12 years as a fan, can I get a robot into the aren

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]

Re: After 12 years as a fan, can I get a robot into the aren

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]

Re: After 12 years as a fan, can I get a robot into the aren

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]

Re: After 12 years as a fan, can I get a robot into the aren

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:

[ewan]

Re: After 12 years as a fan, can I get a robot into the aren

Love the CADs, looks like it's going to be a nippy machine too.

[razerdave]

Re: After 12 years as a fan, can I get a robot into the aren

I have the 3v ones: http://www.maplin.co.uk/Module.aspx?Mod ... Code=WC68Y

[harry hills]

Re: After 12 years as a fan, can I get a robot into the aren

same and the gave good speed on a 7.2v nicad so 11.1v lipo will be interesting

[mark_m]

Re: After 12 years as a fan, can I get a robot into the aren

Lots has happened here today on the robot front. I'd like to say there's been a lot of progress but it feels like its been one step forward one step back all day.
Initially it was going quite well, with the first motor mount made:

All good so far Next I started making the other three motor mounts. After the second one the blade started melting the polycarbonate rather than cutting it. I didn't notice until I'd got to the last one :-( I've no idea what had changed; maybe the blade just started heating up. I'd been using my Dremel with a sanding drum to clean up the inside of the holes so I didn't think it would be too much of a hassle to sand away the molten plastic as the part still looked intact. Unfortunately my only sanding drum ripped as soon as I started sanding it :-(

Taking a break from the cutting and sanding, I next started modifying the motors. I knew I didn't want to use the standard mounts they came with so I took one apart to see if they'd work without the mounts. From a quick inspection of the 250:! gearbox it looked like they would work fine but I'd have to add some washers.to keep the correct motor/gearbox spacing and stop the gears from binding. I then spent ages looking for suitable washers before deciding to make my own. It was only later that I noticed that the 15:1 gearboxes for the drive didn't need washers as the gear spacing was different. Here's a modified gearbox with M3 nuts used as spacers and the micro deans connector soldered on:

So after the first one worked I disassembled, removed the mount and reassembled the other drive motors. That went ok except I found that afterwards one of the motors didn't spin freely. nothing looks bent but it doesn't turn when I apply 12 volts to it :-(. It was also at this point that I realised that whilst I'd bought spare motors, they didn't come with pinions and I haven't got a gear puller
Can anyone recommend a suitable gear puller for removing the pinions off 280 size motors?

After numerous other attempts at making a decent round hole, I finally figured out I could use my router to make the holes, eliminating the sanding. Here's the result:

Nice.

I thought I'd mount the frame rails to the armour (one piece wrap around 3mm polycarbonate according to the design) before deciding how to arrange the wiring. I cut the armour out with scissors and noticed it was probably a little too thick to just bend around the frame rails cold, so I started heating it up whilst bent:

It was going ok until I got a little lazy, didn't keep the heat gun moving enough and overheated it, causing lots of little, weakening, bubbles It'll do for now but I've since decided that it would be a lot easier to work on if the armour was in four pieces anyway.
Here's the assemble:

Not too bad but the armour's a bit of a mess and the wheels don't all point forwards

With it assembled I then started soldering the wiring harness:

Again, not perfect but everything's insulated and secure, or so I thought...

I connected it up to the motors and twiddled with the receiver. Everything worked! Ok the channels were the wrong way round but that was an easy fix. But after I crammed the electronics into the armour, I heard that dreadful sparking noise and a slight smell of magic smoke when I plugged the battery in, plus the blue light of the speed controller went out
I removed everything from the bot, laid it out and checked for shorts. Nothing I could see. So I plugged the battery in again. This time the blue light came on and one motor started moving, but almost immediately there was another noise, the light went out and the motor stopped. Even when I disconnected all the motors the speed controller's light still won't come on when powered up :-(

On the plus side, I weighed everything I've got so far, and, according to my crappy scales, It's 50grams lighter than the cad model predicts

Not sure what to do tomorrow though....

[RogueTwoRobots]

Re: After 12 years as a fan, can I get a robot into the aren

Wow, you're right. For every good thing that happened, there was a setback hiding round the corner to kick you in the nuts.

If it's any consolation though, what you've made so far looks great. It hopefully won't be too far off before we have the first beetle battles

[mark_m]

Re: After 12 years as a fan, can I get a robot into the aren

Progress!

Things seemed to go much better today. Here's the robot as it stands:

Total weight 940grams.
Still to do:
* Side armour
* Side pods to support the weapon motors and mount the side armour to
* Get the bloody electronics into the body without blowing them up
* Replace the aluminium test scoop with a steel one
* Centre section top and bottom armour
* Wire in a removable link
* Decide on a name

Weight is still looking good so I might remake the armour so that its a bit bigger to aid getting the wiring in. Making the armour in four pieces is definitely the way to go - its much easier to work on the robot with just the front and back armour on and its easier to make.

I didn't spot anything that could have caused the speed controller to blow up yesterday. Further testing today confirmed its definitely dead. Is there anywhere I can send it to get it fixed? Its a Dimension Engineering 2x10. Luckily the one I ordered as a spare turned up today so I could carry on building and testing.

The only hiccup today was when I tried to get the Pololu Simple High-Power Motor Controller (weapon ESC) working. Despite it being called Simple it's the most complicated speed controller I've ever used! I had to install drivers on my PC, plug a usb in and then configure it before I could get it to do anything. The configuration utility is actually very good. You can set the zero point, dead band, etc and see what RC pulses it's seeing. There are also various fault states that will cause it to shut down to protect itself, and you can monitor them and set the fault trigger level. It turned out that my original issue was that it was set to serial mode.

Anyway, here's the test video:
http://www.youtube.com/watch?v=7ESMD-ta21s

The lifter's really fast and the nippy drive train makes it a blast to drive! I've really enjoyed pushing cardboard boxes around and chasing the cats.

I'm now feeling more confident that I CAN get it in an arena. The question is: Is there an arena for it to play in? What's the current plan with the beetles?

[mark_m]

not giving up

ok, it's now 16 years.... I've not giving up though.

I'm still working on the same basic beetle design. here's where I've got to:

http://youtu.be/IFppiqhwzJ0
(the bot weighs 900g as it is, the box weighs ~1.7kg)

http://youtu.be/cTKPTED1fo0
I've now got access to a 3D printer, and occasional access to a mill and CNC router, so I'm prototyping with the printer, then will remake in polycarbonate/titanium. So far the 3D printed parts have fit together well and I think the basic design is sound, but there's a few things I need to fix:
*The belt drive for the lifter slips too much and is too stretchy. I need to change it to a reinforced belt, or a small timing belt or chain. Any suggestions?
* the press fit pulleys/wheel hubs keep slipping. I guess I need to add a grub screw or glue them
* the trims seem to drift with time. I couldn't get Elevon mixing on my DX6i to give me full speed forwards, so I'm now using an onboard mixer. With both setups though, the trims seem to move over time. I got the trims set up before the above video, but by the end it was creeping backwards when it should have been stationary. I've never seen this before. The receiver is an orange r400 and the ESCs are botbitz 10A.
* The only bit of the bot that gets hot is the ESCs. The motors are the ebay 1000rpm gearmotors with one 10A ESC per side. Do people use one ESC per motor or is one per side normally ok? I'm worried that arenas might be grippier than my kitchen floor, increasing the load on the motors and ESCs.

When's the next beetle event?
At this point I'm tempted to just put the 3D printed version in the arena, just to get experience and see what breaks!