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Glen
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You mean you haven't worked out the anti gravity drive yet? Ha, amateur Wink

I think original cobra was a fair bit smaller than nc, the drives would've been lighter and the battery was about 1.1kg, so not a huge difference.

Plus the 3mm hardox is more like 3.7mm thick for your weight calcs
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Post Thu Jul 16, 2015 10:48 am 
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Valen
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Well not anti gravity, but I do have an induction drive robot plan if anybody built a steel floored arena

Thanks for the tip on 3.7mm
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Post Thu Jul 16, 2015 7:55 pm 
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Valen
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3/4 have turned up


One of them has the old style face mount on it and some cool looking brush holders.

The other two the motor can is just held in 2 places, I'm going to look at some high temperature epoxies to try and make it stronger. The face is an aluminium casting by the look of things otherwise I'd weld it.
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Post Fri Jul 24, 2015 4:15 pm 
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Nick
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Are you going to support the back of the motors? From experience with 550 motors, as long as the can is supported at the back, the front can come loose and wobble around a fair bit without causing any problems. The epoxy sounds like a good idea and I would make a plastic support for the back that also stops the brushes from popping out.
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Post Fri Jul 24, 2015 9:05 pm 
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miles&Jules
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seeing this from a possible opponent angle …i think the epoxy sounds like a great idea.
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Post Sat Jul 25, 2015 10:53 am 
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Valen
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Dewalts and hoseclamps, there is something wrong with me.
Still hopefully better than the tie rod setup.

And something wrong with the team Delta mounts too, the chuck is slipping somehow. I had hoped to have everything running today but no joy, the gearbox is one of the most central parts. It's even brand new, turns out dewalt still has stock of them, pair for $110 pickup from the local tool shop.

New battery protector too

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Post Sat Oct 03, 2015 12:41 am 
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Philip
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That all looks very neat.
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Post Sat Oct 03, 2015 2:35 am 
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Valen
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Wow I even have spares of things.


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Post Sat Oct 03, 2015 2:53 pm 
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seanet1310



Joined: 08 Nov 2006
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Far too prepared.
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Post Sat Oct 03, 2015 5:13 pm 
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Valen
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Came 2nd after getting stacked by nick,
No real damage, still not driving right though, the wheels were running of the sides of the hubs with help from Nick and everybody else there that was sorted but it still seems to bind up randomly.
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Post Sun Oct 11, 2015 10:49 pm 
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Jaemus
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Nice work Jake!
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Post Thu Oct 15, 2015 8:02 pm 
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Valen
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I'm thinking perhaps some of my issue is I haven't re-timed the motors, and as I speed up I run out of top speed on one side before the other making the bot spin out. I don't really want to re-time them as it looks like it makes the whole back of the motor weaker.

It also lacks the speed of cobra which is :-<

I'm thinking of upping the voltage, to get more top speed, but I need some form of current limit. I was also thinking of adding some system so that the sticks control wheel speed not power.

2 birds one stone, glue a teensy magnet to the back of the motor shaft, put a rotary hall effect sensor on there and we can sense motor RPM, rather than directly measuring current (another thing that can fail, and hard to do at hundreds of amps of PWM) just infer the current from battery voltage and motor RPM, then limit the signal going into the TZ85's to stay under some magic number that keeps the smoke in the motors.

Not as good as actual current sensing but easier to pull off I think.
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Post Fri Oct 16, 2015 7:45 am 
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Nick
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If you are going to add an MCU, you could get it to compensate for the timing differences automatically. If you go as far as using hall sensors, it would be easier to embed the magnets in the side of the wheels, where they also get shock protection. You could also fit more magnets for better resolution at low speeds.

The hall sensors could really help with digitally re-timing the motors by comparing the R/C signal with the actual RPM on each motor; you would have a hillbilly gyro Smile
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Post Fri Oct 16, 2015 9:27 am 
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seanet1310



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Go all out and feed a gyro signal in as well with the motor/wheel RPM and process this as well in the MCU to enable super straight movement without the gyro itself getting heavily in the way,.
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Post Fri Oct 16, 2015 12:49 pm 
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Valen
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I thought about using a gyro, and I'll leave room to add one, but it feels like if the wheels are both going the same *distance* (even better than RPM, as error won't accumulate) then most of the error should be taken out and you won't need to worry about the errors a gyro would introduce.
Though I guess a gyro would perhaps help counter spinout, hmm I'll have to think about that some more.

@nick
I was hoping to use something like
http://ams.com/eng/Products/Position-Sensors
for the sensing, but even with just a regular hall sensor you get 2 pulses per motor RPM which after the gear reduction should be pretty good, (also I've learnt from the mill backlash between motor and sensor is the debil for PID loops lol)

I'm going to look at making NC2 as well, victory through superior numbers.
NC2 would be brushless drive, which kinda solves the whole "sensing motor position" thing for you to some extent. And of course moar powah.

I was really hoping glen could have a drive of NC before the arena was packed up but we ran out of time. Anybody have an idea how to test drive a pushy bot without eating the wheels on concrete?
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Post Fri Oct 16, 2015 4:37 pm 
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