XRobots blog

XRobots.co.uk blog

Thursday, June 29, 2006

Legs and wheels

So, android 9 is almost walking. I have the top section of one of the legs pretty much doing the right thing at the right time, just need to do the same with the other and it will locomote. If I get around to doing the bottom sections of the legs it should walk quite well.

I've been a bit busy recently doing stuff over at www.914pcbots.com as I've established admin rights (for now...). Hopefuly whiteboxrobotics will deliver the first shipment of robots soon and then we'll have a full blown fan site. There are already 100's of registered users although most are 'lurking' for now. From the stats is looks like there are around 300 visits a day so it will be good once the product is available.

On top of that I've been thinking about creating a new android called 'Android X' as it will be the tenth and also matches the Website name of XRobots. Android 9 will probably be ok but I usualy get bored at this point in development and have better ideas.

I'd quite like to use actuators/motors on all the joints instead of having passive ankles because that's the hardest thing to work with. I'd also like propper knees again rather than my on-going parallel mechanism that I've used since android 3. I quite like the balsa wood construction but next time I'll use RE/RS540 motors and make my own gearboxes out of plastic gears, using skateboard wheel bearings for the output shafts. It will look a bit like the RoboOne robots that use R/C style servos but scaled up to about 4 feet / 1.5m tall.

Saturday, June 03, 2006

Working as planned so far...

The current situation is that the android is able to lean side-to-side a few times at about one second intervals between leaning each way, if the gyro says it's not stable enough to lean back the other way after that second then it waits 100ms (0.1 seconds) and checks again... Then another 100ms until it the gyro data is between certain constraints. Basically I'm trying to find the Zero Moment Point (ZMP) which is when the gyro effectively reads 'centred' and there is no momentum in either direction. You can tell some delays are longer than others because you can hear the relays clicking, a bit of fine tuning to do though because although it doesn't fall over it's sometimes close so I need to turn up the sensitivity I think.

I've got a few things to resolve with mounting the batteries inside it which I'm now using instead of the mains power supplies - and I've had far less trouble with the Picaxes hanging due to the long wires and spikey load/unhappy PSUs/back EMF/noise etc. One of the gear boxes got damaged when the motor got stuck 'on' due to this and the pot shaft that was attached to it also sheared as a result... So there's no issue with the strength of the gearboxes, I just have to be more careful not to abuse them. Might implement end switches at some point.

When the replacement gearbox arrives (and my other Picaxe board / chips as mentioned in the article), then I'll be hopefully putting up a video of it leaning side to side with some degree of dynamic control. All that remains after that to make it walk will be triggering the leg controllers to do the right thing at the right time during the main dynamically stable leaning loop.

Sunday, May 14, 2006

Gyros and walking stuff

I've been thnking about how best to get my android to walk as it's very light weight and the motors move quite quickly. I think I'm going to get a gyro like the GWS PG03, which appears to output a servo-compatable PWM signal as you tilt/turn it which is cool for picaxe interfacing.

Then I thought about how to integrate it into the robot because I have two hip motors for side ways movement... I guess ideally I need three gyros - one for each leg, and one in the body - all of them for side-to-side movement. Then the main picaxe or whatever can read them all to work out how to position the other joints. However, for now I don't really want to buy 3 so I'm going to put one in the body and just use that as a kind of safety-switch to stop it tipping over.

I'm going to have my 3 picaxes driving the 6 leg motors. One will be interfaced to the gyro and be responsible for leaning side to side with the two hip motors - back and forth in quick sucsession with hard-coded postitions. If it tips too far (from the gyro data) it will pause before tipping back the other way so it doesn't further over balance. It could also set of an alarm if it's going to fall over so I can catch it. Once this works ok I will use spare output pins going high at stages during the side-to-side motion to trigger the other two picaxes which control the 4 leg motors (two each). These will 'play back' each legs' motions to take steps while the weight is on one foot (small movments to start with to kind of coax it along).

I'd like to also modify the hard-coded positions of the side-to-side hip motors depending on what the gyro says but I need to think of a way to stop them sort of getting out of line with each other... i.e. if it leans until the gyro says stop then how do I make sure the legs are evenly spaced... probably by making sure they aways return to a fixed centre position and taking my chances.

Once all the main parts of the android are made then I'll be able to start testing since I'll have most of the weight on board. I'll probably start a new article for the testing and some flow charts to go with various control methods.

Monday, April 24, 2006

Back in the land of robots

I've pretty much finished the house, should be having carpet fitted this week, so I'm back in the land of robots. I did attached the motors to my (robot) legs last night so there'll be some more pics up soon...

Wednesday, March 29, 2006

Robot making equipment

I've just started a flickr account to display pictures of my house (before/during/after) that I'm currently decorating. The 'before' photos are on the higher page numbers and new ones will get posted as I do stuff. It's taken me since December to get this far as I only have my evenings to work on it and it was in a state, I have about a month to finish.

I got my laminate flooring down in my spare room last night so now I can move in my robot making equipment and have all my tools in one place. The next thing is making aluminum motor mount brackets so I can't cut them with a craft knife like the balsa wood.

Monday, March 20, 2006

Mr Stick Legs

Mr Stick Legs is not dead by the way...

...He's just resting while I decorate my house. I've actually done some more to him than the latest update but it's not that far off walking again with an additional two motors per leg so I'll probably update the article once It's working again. Only two bicycle brake cords left to add and a couple more bungees... I'm considering making the upper body/head/arms out of balsa wood and card like Mr Featherweight but we'll get him walking again first.

It would be good to make some human sized hands and actually finish them this time, I'm quite happy with my new found modeling methods so Mr Stick Legs will be an ideal platform to carry them.

Paint and motors

I spent most of the weekend buying about 10 pots of paint in various creams and red/purple for my house so that will keep me busy this week.

I had ordered some motors for the latest android which arrived on Friday. They would probably be ok with no weight from the body on top but I have decided to keep them for the arms for now and so I have ordered some slightly larger ones for the legs which I should hopefully get this week. They are the plastic Tamiya ones that come from British Robotics. They appear to be quite good value for money but basically I was just being cheap the first time around so I bought the smallest ones they had, the new ones will be these. I'll put some pictures up hopefully later today of the ones I have.

Tuesday, March 14, 2006

First post

Hello everyone, you're probably reading this because you clicked on the link from www.XRobots.co.uk, or maybe you just stumbled upon this blog...

For any robot people who check my site on a regular basis you'll notice that there haven't been so many robot updates recently. This is because I've been re-decorating a house that I bought in December and that I am moving into shortly with my girlfriend who is relocating approx 140 miles to London at the same time. I've had to refit the kitchen and bathroom from concrete floors / floorboards and bare plaster walls up... all the old stuff had been there 20 years and had to be torn out and thrown away. I still have to paint every other room and do the flooring but the worst is over so there should be time for more robots again soon. Might post some pics of the before/after somewhere...

So, keep checking back for robot updates, I'm still here... just a bit worn out from doing all the house 'mens work' myself.