The Unnamed (FW)

[Pinski1]

So here's that update I promised...

Its been a while and the robot has been somewhat dormant. Mainly because I just couldn't figure out a way to know where the lifter arm was so I could then control it without jamming it up or down. I had thought about using shaft encoders but they're a relative measurement and need an indexing signal so the ESC wouldn't know where the arm was if had just been turned on, say as a result of a momentary power loss.

However an off-hand comment from a friend at Cambridge Makespace got me thinking, could I attach a linkage which would then turn a variable resistor. After a bit of maths, a bit of head scratching at SketchUp and a laser cut tester I found a set up that would work!



After some careful machining and some painful filing (D shafts are really cool but an arse to make) I'd got my linkage attached and now had a variable resistance based on the position of the arm. YES!

The next big step is to get the Tz-85A working. Looking at the modified Tz-85A code here. It seemed really messy and completely ignored the 16bit timer1 in favour of an 8bit timer0 with an 8bit variable to extend it. So I rewrote it. This was a painful choice but I got it working pretty well last night. I just have to sort out the servo code to process the variable resistance and run a very basic control loop. Oh and write the calibration procedure.

This is my current set up:



Once I've got the calibration code somewhat sorted I'll post the GitHub repository. Unless you guys want to trial the current firmware?

Oh and I've entered it into the Burgess Hill competition in April, eep!

[harry hills]

So much legit robot going on there. Tempted to come to burgess hill just to see it.

[shakesc]

Nice work, looking forwards to seeing this

[Eventorizon]

Another reason I stalled is while conducting extensive driving testing (aka ragging it around to scare people) I killed the battery. My 18.5V 5AHr 5S1P battery now has a voltage of 13.92Volts, 4 of the cells are at 2.73V. It's dead, pushing up the daisies etc.

Low Voltage isn't a total killer for a Lipo. Due to a faulty charger we drained 2 of our 5S 2600mAh packs down to less than 2.2V per cell and were able to recover them using a Pro-Cell 10 charger (It can run recovery cycles and I think we even ran a NiHM cycle just to force in some power) They have worked faultlessly since in over 10 fights and countless demo's.

All that said, be careful, and you can't do this with a cheap charger either.

Lifting mech is looking great though!

[teamstorm]

That's exactly how the arm on Storm II works, it uses a 10k Pot mounted inside the gearbox block that drives the arm mechanism to relay end-stop (not position) information to the speed controllers. We avoided creating a 'giant servo' approach where the arm would fight to stay in whichever position we wanted it in for fear that in a fight that's just not practical, something jams the arm and you're looking at a stalled out motor with very little you can do about it.

Can't tell you enough how you do NOT want to run that as a giant positional servo

[Pinski1]

...not practical, something jams the arm and you're looking at a stalled out motor with very little you can do about it.

Well bugger! Okay so I've fiddled with the code and got that working with the Arduino acting as the limiter, worked perfectly got it up to 75% speed in both directions. Tried modifying the code in the Tz-85A and NOPE. Power supply kept tripping despite the speed being limited massively. Its probably due to the power supply only has a current rating of 5 Amps, RS550s are thirsty!

Low Voltage isn't a total killer for a Lipo.

Unfortunately the pack is now gone into the waste disposal bin in the sky. It's a painful lesson which should help me remember to avoid it in the future. How do others manage this? Do you guys have under voltage lockouts? Keep a battery monitor permanently attached?

So much legit robot going on there. Tempted to come to burgess hill just to see it.

Oh I'm sure it'll get totally scrapped in its first fight! But thanks!


Right, so a quick diversion, another big problem was an elegant way to do the power distribution and the removable link. I wanted a low profile removable link and had forgotten to add a fuse so I thought I'd combine the two!



The blue block on the right is a 3d printed ABS Maxi fuse holder, it holds the fuse in pretty securely as well as guides it into the blade connectors pretty well. It's a little awkward getting it out but that should stop it falling out in battle! The white blocks to the left are 2 ceramic terminal blocks, after it turned out my cool spring loaded terminal block was pants I needed a replacement and these are it. They're rated for high temperature and current and should do great. I'm considering replacing my crimped wire jumpers with insulated copper bar but they work for the moment.

And here is what it looks like powered up with the chassis in the way.



The red 4mm HXT between the battery and the fuse on the right hand side of the photo will be replaced with XT90 connectors eventually as it keep the power connectors all in the same family. They're also technically rated for a bit more current.

As you can see things are quite tight and I've not even got the lifter ESC mounted yet! Even so the red power indicator is fairly bright and I'm hoping that it should be sufficient but would love some feedback, what do other people use?

I'm hoping to get the limiter ESC code working this evening and then I can put a little video of it "training" (aka banging into everything while enthusiastically raising and lowering the lifter).

[Mouldy]

Thats looking really nice!

[Eventorizon]

Unfortunately the pack is now gone into the waste disposal bin in the sky. It's a painful lesson which should help me remember to avoid it in the future. How do others manage this? Do you guys have under voltage lockouts? Keep a battery monitor permanently attached?

Some ESC's have built in voltage cut outs, usually at 3V or 3.2V depending on the original intended application, so the Castle Creations ESC's we have in Conker and Binky will cut out if the total voltage drops below 3.2V per cell.

However, note I said TOTAL voltage. We had 2 packs, one was fine, the other undervolted. Between the two of them, they exceeded the 32V cut off point for a 10S pack even though one pack was way down and the other way way up. There is no real way around this when using 2 packs that is simple to implement (that I am aware of).

Single cell machines can have one of these installed: https://www.dimensionengineering.com...cts/cellshield But it can only be linked to one of the ESC's as its meant for Cars, Helicopters and Planes that only have 1 drive motor. You could put it on your arm's esc so when the arm stops working you know you are on the limit and can just tap out to save the robot.

Aside from that, baring telemetry, there isn't really any way to tell, until your robot goes all sluggish, which is usually to late. Over the events we have done you get an idea of how much power you are using. If you keep track of fight times and then note how much power is put into the battery when its recharged you can work out how much you need.

As an example, if you have a 3 minute fight and use 1200mAh, a 2 min fight and use 1000mAh and a 1 min fight and use 450mAh then you know you are using between 400mAh and 500mAh per minute. So if you are having 3 min fights that's 1500mAh, taking the worst case scenario, but you also need a safety margin so a 1800mAh pack would do. I hope that makes sense!

[Pinski1]

Looks like there may be a market for a battery saver/fuse, *begins furiously planning* I wonder if Ranglebox would stock it. Connect to both the battery power connectors and balance port and disconnect the battery on over current, over voltage or under voltage.

Anyway tried connecting up except this time with the battery supplying it so as to provide a near limitless source of amps however it just went berserk. This is bad, I'll try and get an oscilloscope on it tonight to see what's happening.

[Eventorizon]

Looks like there may be a market for a battery saver/fuse, *begins furiously planning* I wonder if Ranglebox would stock it. Connect to both the battery power connectors and balance port and disconnect the battery on over current, over voltage or under voltage.

I would say its more effort than its worth. Given a bit of maths and experience it's not really an issue, and designing it for sale would mean taking account of numerous wiring configs, power inputs and ESC arrangements, so lots of effort for minimal gain.

Oh, and define Berserk? I can't see you needing an oscilloscope. Its probably something very easy to fix. Despite the lack of info, if by berserk you mean it drove by itself or wouldn't steer properly then check your drive ESC's are on the ELV and AIL channels, you have it V-Tail mixed and you have the trim set correctly when you bind so it failsafes.