Weapons of mass distraction.

While I’ve had the last few months to freak out about having no motors and therefore essentially no bot, I’ve had plenty of time to try and distract myself and design and build a range of add ons to cope with some fairly stiff challenges in this year’s competition.

I built a 4-way sensor rig from standard ultrasonic sensors. The wiring is pretty um… intense, but it does work and reads distance in all directions. I’ll be using this for the straight line speed test and the maze.

The wiring maze begins…..

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All wired up….

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I’ve also got a mount for the line sensors sorted and the code working nicely for that (fingers crossed this works on the day!). I’ve also got a simple holder for the golf challenge, although I suspect there may be far sneakier / trickier hazards than this will cope with! :/ The one on the left is the clamp for Pi Noon… Looking forward to that one.

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Skittles was great fun last year, and my ‘ball cannon’ worked well enough, sadly my driving let me down and I knocked the ball away from the bot and fluffed a shot. The ‘collect the ball’ component of the challenge has forced me to come up with something to avoid this completely this time round.

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The simple arm / servo arrangement should prevent the ball rolling away, and the spring in the tube has enough kick to give the ball a good whack!

Armed and (slightly) dangerous…

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I’ve got the bot driving properly and the mecanum wheels are performing really well – such a relief at this point. I’m now (slowly) working on the autonomous challenges and rapidly running out of time. Going to be a frantic dash to the finish line. I reckon I’ll get there :-)

I’ve got a bot that can compete and even with all the difficulties I faced, I’ve learnt so much again through the the build and it’s been really fantastic to be involved in Pi Wars again. I love the social camaraderie, particularly on Twitter. Very much looking forward to seeing old faces and new next weekend.

I’ll be there for both days, do come and say hello. I’ll be the one with the panicked look cos his bot just * shot out the door / took out a small child / knee-capped Eben Upton (*delete as applicable)

See you all next weekend!

Until then…

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Motor Woes – Part Deux

It never rains…..

I have not as yet managed to assemble a complete set of four matching motors in the six months I’ve been in preparation for this competition. Unreal.

And, with 10 days to go, I managed to strip two of the gear boxes on the motors I have. I took them apart and discovered that the gears in my ‘metal gear motors’ were in fact…  plastic. Seriously? – After how long it took me to find them?

Something’s definitely not right…

Ok… DefCon 1 level panic time. Some great suggestions on Twitter (thanks folks!) and some fleabay scouring actually brought these beauties to my attention thankfully pretty quickly…

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Not cheap, but sooooo pleased I found these, 24hrs ago I was pretty much dead in the water.

These motors are 12v and I have been running at 9v. I’ve stepped it up to 10.5v which is the maximum voltage the Zeroborg controller I am using can handle. They are nice and torque-y and are rated at 500rpm, I reckon I am getting 430rpm (ish) at the voltage I am using.

Although I built the motor mounts to be removable it still required a complete strip down of the chassis to remove and replace all four motors (again).

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I’ve 3D printed a fake AA battery and run a wire through it so I can use an 8 cell holder with only 7 cells in it to give me the required 10.5v

Works a treat!…

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I’ve also removed and replaced the rollers for the ninetiteenth time. This time to add some thread lock. The wheels do put some fairly significant forces through the rollers and they’ve had a tendancy to spit bolts on the odd occasion so I took the opportunity to tighten everything up.

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Anyhoo. Another 48hrs flies by, and I have rarely been so grateful to be back where I was two days ago. Onwards – I still have a ridiculous amount to do. At least now I have four matching motors!

I’ll hopefully get time for one more post where I’ll do a quick overview of my wild and frankly heath-robinsonian attachments for some of the challenges.

Until then….

 

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My Achilles Wheel…

As I’ve previously mentioned my last Pi Wars bot was rudimentary to say the least. This time I wanted something that would push my skills further and also result in a better designed / built bot. There’s nothing like jumping in at the deep end so when I got my hands on the 3D printer last year, I had an idea. A mad, stupid, almost impossibly, ridiculously complex idea but hey – this is Pi Wars, right? I’ve kept this largely under my hat during the development of these as I honestly wasn’t sure I could get them to work…

MECANUM WHEELS!!

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So, I saw PiBorg and their mecanum wheeled robot at a couple of events and pretty much fell in love. This combined with witnessing the performance of the omni-directional bots last time was enough to convince me to attempt to do something similar. I looked around and found prices for mecanum wheels to be more than a little eye-watering and therefore decided to see if I could 3D print some. It became pretty clear, pretty quickly, to be honest that the full design is waaaaay beyond my capabilities so I adapted an original set I found on Thingiverse which were just so freakin’ cool.

The first frame appears on the printer…..

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They were designed for Lego motors originally so I adapted the hubs to work with Pololu 4mm hubs and gear motors. I also reconfigured the roller attachment to work with M3 bolts, rather than Lego axles.

Roller up…. Roller up.

Each frame takes around 7hrs to print at 0.2mm resolution – fortunately all four printed first time with no errors.

And now the fun really begins…. 4 Wheels. 8 rollers per wheel, 2 bolts per roller.

I’d originally intended to print in NinjaFlex – a really cool rubbery 3D printing filament but sadly it turned out my printer couldn’t use this so I had to get creative.

Printing the basic rollers….

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(Each roller takes 19 minutes to print)

I can print in PLA or ABS, both of which are basically solid plastic and therefore completely unsuitable to be used as rollers as they have no grip at all. So – a covering was required. To quote myself and many other Pi Wars contestants – ‘How hard can that be?’

As it turns out, very. Annoyingly, swearingly difficult actually. I have now tried and tested seven types of covering. That’s all 32 rollers removed, coated, replaced, tested. Often twice – just to be certain.

Hanging ’em out to dry….

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The list of what didn’t work includes…

  1. Balloons
  2. Heatshrink – thought this was guaranteed but failed completely!
  3. Rubber Cement – cracking idea from Graeme C. – sadly it peeled right off.
  4. Latex – dipping each roller many, many times to build up the layers. Very weird stuff – and ripped straight off.
  5. Grip Tape – stuff skateboarders use. Useless, wouldn’t adhere to rollers at all.
  6. PlastiDip – rubber coating stuff. Took ages, cost a fortune. And ripped off, again.

It can be seen from the above that coating and grippiness wasn’t an issue, durability was. So, as I was about to throw in the towel, Mark from Astro Designs came up with idea number seven…

7. Self Amalgamating Tape – aka plumbers tape.

And….. we have a winner!

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Here’re are the rollers wrapped with tape and ready for testing. It had become a proper love hate relationship with these damn wheels by this point in the process.

Thankfully, I think we’re looking good. Whilst the bot is ridiculously ‘slidey’ the wheels do actually work.

I conservatively estimate I have spent 100+ hours on the wheels alone so I am thrilled that I have a bot with ‘proper’ mecanum wheels. Whether this offers any advantage in the competition remains to be seen!

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The tape offers enough grip to get the bot to move and it’s durable enough not to tear straight off. It’s a complete riot to try and drive the thing however. It may yet be christened ‘Uncontrollabot’ !

It has of course made autonomous driving and the associated challenges much, much harder than they may well have been. But hey, we’ll cross that bridge when we get to it.

In about two weeks time :-O

Until next time….

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Lightning does strike twice

Just a quick update this time. Got a lot on at the moment!

If you were around for the last Pi Wars you may remember I fried a Pi for the first time ever whilst mucking about with relays for the skittle ball release mechanism. It was sad. We had a minute’s silence. RIP RPi.

Weeeeell, it would appear I doggone went and did it again. Nooooooo!! This time it was whilst trying to hook up the Adafruit servo board (which I’ve used successfully several times in the past.)

There was smoke this time too. Proper thick, acrid, really not good smoke type of smoke. Rapidly followed by lots of frantic wire pulling.

Was undoubtedly a classic ID10T error. A quick aide memoir for myself and others:

9v > 5v > 3v3

This is important. It goes wrong quickly if you mix them up. Very quickly.

I was in all honesty surprised when the Pi actually booted up again. Sadly though, a quick check of the i2c deelybob (that’s a technical term I think) revealed that all was not well…

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I’m not sure therefore if it’s the i2c driver on the Pi that’s gone, or whether its the servo board. In reality, I’ve not had time to check, I swapped out the Pi for a fresh one and have limited myself to using the hardware PWM on GPIO 18 of the Pi. I’m only running one servo that holds an arm to hold the ball in place (hopefully) for the golf and skittles events.

I had another moment earlier this week when, on reviewing the challenges on the piwars.org site that I realised that there had been a small, but rather flippin important change to the skittles challenge – someone put a turn in the course! I’d not seen the important ‘competitors must collect the ball and then…’ bit. The wonderful @GeekyTim ‘fessed up on Twitter when challenged and admitted that it was indeed he who had added a little something extra. This should make it a lot more interesting and requires some thought in actually controlling the ball to even get it as far as going in the direction of the skittles.

I’ve still got a long way to go, have been manically designing and printing a wild and wacky range of attachments to serve in the array of challenges. More of these next time. The bot is being assembled and reassembled repeatedly as I test, fit and retest different configurations. I’ve got most of the manual challenges sorted now and am working on the challenges that require some form of autonomy. I *may* have made these an awful lot more difficult than they reasonably should be due to a critical design decision I took very early on in the process. I’ll let you know.

So – onward and PiWar’d. Ermm…. did I say there’s only two weeks to go? Gotta dash – I’ll catch up with you all later.

Until next time… (more…)

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Chassis-tastic!

Finally feels like things are starting to come together. Literally. Since my last bot was made from two cobbled together project boxes, any amount of design is going to be a step forward. I’ve continued to experiment with OpenScad and am really loving it. There’s a really good cheat sheet here that gives you pretty much everything to design anything of any shape. It’s really a very powerful FREE tool and tbh makes much more sense to me than the AutoCad type programs. I’d also previously tried SketchUp and found it to be the same type of thing with a million incomprehensible buttons and a very steep learning curve. For my purposes OpenScad suits perfectly.

So, I’d made the motor mounts (for non-existent motors at the time) and wanted to build a fairly simple chassis to mount it all on. To the 3D printer, Batman! I put together a very basic shape, with holes for the motor mounts, and then, in trying to make it look at least a little less basic, began experimenting with chopping bits out of it. This can bo done really easily with the difference() function in OpenScad that takes one shape away from another.

I then saw fairly quickly where I wanted to go with this and….

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Behold – X-Bot is born! :-)

I am printing in PLA with 20% fill, which gives plenty of rigidity without taking a age to print anything. Got to admit that having the 3D printer is an absolute gem. Being able to conceive an idea, design it and hold it in your hand a very short time later is still pretty science fiction to me!

The motor mounts went on really nicely. I’m really pleased with these considering my motors were held on with hot glue last time!

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And once all four were mounted…

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I started to lay out the electronics to get an idea for the spacing etc…

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I also attached the wheels for the first time – Yay! For the first time it actually looks recognisably like a Pi Wars bot.

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Was also REALLY pleased to see my calculations were indeed correct and it does fit on an A4 sheet of paper – phew.

So, the basic chassis and control mechanisms are complete. I *still* have motor nightmares to confront. The seller who owes me a back order is yet to come up with the goods so I may yet have to find another plan.

I’m going to focus on the manual challenges next as planning / coding for the autonomous challenges is a non-starter with un-matched motors. I’ve got an idea for the golf challenge and am going to rework last year’s skittles cannon so hopefully can sort those two fairly quickly. I’m designing swap-able mods for each of the challenges, I spent too long having to reconfigure the bot during the day last time so want to avoid this as much as possible.

Can’t believe there is sooooo little time left!

Next time – Weapons of Mass Distraction.

Until then….

 

 

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Motor woes… And tantrum throws.

We do this because we love it.

We do this because we love it.

We do this because we love it.

(Keep repeating the mantra)

It’s not that bad, but some parts of the process can make you swear a little. Additionally, it’s 48hrs to the Pi Party, I’ve got loads of prep left to do – and have had lovely tonsillitis for 3 days. Seriously hoping the antibiotics kick in soon!

So – four motors right, just four little motors. No problems. So, I started ordering motors back in November and after two hopeless ebay sellers took TEN WEEKS to fail to deliver anything to me at all I was getting a little sweaty by the time the new year crawled round. So, third time’s a charm (as the saying goes) and I found another supplier who actually delivered the goods in about a week.

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Last year’s motors at the front – new ones behind. Ooooh – look at the shiny shiny!

I was sooooo happy to get my hands on these then a few things started to dawn on me. The motors are 12v. I am using a ZeroBorg from PiBorg, the very neat little 4-channel controller they first launched as a Kickstarter campaign. Turns out the ZeroBorg can only take a maximum of 10.4v, so I am actually running it at 9v. Bang goes 25% of the power going to the motors immediately.

In addition to this, the motors are rated as ‘300rpm’ (when running at 12v) So I expected around 200-225rpm at 9v. This I would have been happy with. The motors I used last year were 130rpm but really torque-y. These new ones actually turned out to run SLOWER?!! Whoever gave these their speed rating needs a good talking to IMHO!

Back to square one.

Another year, another supplier (Ireland this time)….

‘Hi, you have 300rpm, 6v motors?’

‘Yes’

‘And they’re definitely 300rpm?’

‘Oh, yes’

‘And they’re definitely 6v?’

‘Oh, definitely sir’

Fantastic. So, I order and a week goes by. I am juuuust getting antsy when a parcel lands on my door step.

Containing three motors.

And a note ‘Sorry – we’ve only got 3 of those atm, we’ll send you the other on back order when we get it – possibly by March.’

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Are. You. Kidding me.

(Oh – it’s now March, and I am still waiting.)

So, I find my FIFTH supplier, in the US this time, who has the exact same motors that I have three of, but at a premium price plus US / UK shipping costs. I therefore spent a lot more than I should to get a matching forth motor. In fairness to the seller, he shipped immediately and it arrived within a week.

And guess what? – The SAME motor, from the SAME manufacturer, with the SAME label actually has a 6mm shaft not a 4mm as the others do. And it runs significantly slower than the other three. Utterly frustrating, but can’t really blame the seller for that one, although QC at this particular manufacturer obviously leaves a lot to be desired!

So, with 6 weeks to the competition, I am yet to find a fully matching set of motors. I have compensated in the code to allow for this, but it does mean slowing the other three down to match which isn’t really great – I certainly won’t be winning any speed runs I feel!

One a positive note, I’ve designed my own motor mounts for standard 25mm gearmotors, I’ll put these on Thingiverse so they’re available. Very pleased with the way they turned out…

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I’ve also got the Pi Zero / ZeroBorg wired up and have started tweaking the code. I’ve also got a PS3 controller set up for manual challenges. This is a significant step up in usability and complexity from last time round. Think I’m also going to need a lot more driving practice!

 

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Next time…. Get it together, man. – Time to get chassis-tastic and try and actually build a bot!

Until then…

DP.

 

 

 

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