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Jolt & friends - Team Overkill - NSW
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Glen
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Joined: 16 Jun 2004
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Place the robot with its test wheels on the floor and attach it to a spring scale attached to something immobile then drive foward. Doesn't get much more empirical than that.
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Post Thu Apr 06, 2017 12:00 pm 
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Nick
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Location: Sydney, NSW


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I used that technique on Scissorhands - it worked well even though the results were depressing. The problem here is that the new, wider wheels don't fit in Mr Mangle's wheel wells and the new frame doesn't exist yet. If the tests show any promise I will probably make some narrower wheels for the original Mangle - it needs all the help it can get to drive straight on a bumpy floor.

Another idea for the wheel tread is to paint on liquid polyurethane while the wheels are slowly spinning in the lathe. I can see that getting very messy but I know the urethane makes quite a good tread from the wheels I made a few years ago. The advantage here is that the wheel diameter can be any size I need and not just what is available commercially.
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Post Thu Apr 06, 2017 1:03 pm 
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Nick
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Printed wheels:

The 30 hour print is finally finished and the results are excellent Very Happy. There is some ugly stringing inside the spirals but the way the wheel rides is far superior to the test with hexagons - I'm not bothering with them again.



The wheel is still a bit too firm so the next one will have 4 or 5 less spirals.
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Post Thu Apr 06, 2017 5:41 pm 
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Nick
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Wheels:

I printed another Ninjaflex wheel with less spokes this time. After a false start that got to 47% before a power cut Mad, this one is almost perfect, with enough flex to give several mm when the opposite corner is lifted. The test tires are arriving from HK tomorrow so the next step is testing the grip.

Mr T:

I have been very lax with the sportsman bots and the Vivid event is creeping up on me, so its time for some progress. The power wiring loom is finished and the next step is to wire the ESCs to the motors. The Burket valve also needs wiring - that's probably going to take more time than the rest as the Arduino MCU needs programming.

Sawnado - the bot that just won't die:

As there are only 12 sportsman bots registered for Vivid, I might as well throw Sawnado in there Smile. I found a new blade that doesn't have tungsten tips and fits into the rules so it may do better this time. It's main problem has always been a lack of grip and unreliable motors, so I have a plan to convert to brushless motors and custom wheels based on the ones for Mr Mangle. I have tons of weight to play around with so maybe other mods will be possible.
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Post Sun Apr 09, 2017 7:27 pm 
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Nick
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Printer upgrade:

The Printrbot upgrade took another step today:



The MDF base is almost finished; I wanted it to look good so all the tabs & slots are filled in with epoxy and sanded flush. After two coats of paint, they are almost invisible the the base matches the finish on the printer quite well.

Mounting the printer to the base is not working out so well; hiding aluminium angle inside the printer base just didn't fit, so they are exposed on the outside. Maybe the ywill look less ugly after they are spray painted.
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Post Mon Apr 10, 2017 1:42 pm 
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Nick
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Wheels:

The tires arrived from Hobby King extra fast and they are working out really well. after cutting the side walls off, the remaining tread is exactly the same width as the printed rim and the tread stretches over the rim for a tight fit.



The grip isn't that much more than a Colson wheel, it might improve with some driving but even a little extra grip is very welcome. The tires have increased the wheel diameter by 5mm, so the next step is to print a smaller set of rims - that's another 52 hours on the Wanhou Sad. That should be enough time to finish up wiring the MDF test frame for a drive - super exciting!
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Post Mon Apr 10, 2017 3:50 pm 
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Nick
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Wow, over 1 million views - thanks guys! Very Happy
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Post Mon Apr 10, 2017 6:48 pm 
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pilleya



Joined: 31 Mar 2016
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Location: Sydney


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With the prints taking so long you should probably try get your hands on an old server UPS or something. Plenty of old UPS out there just need a few new SLA's to live again.

Or put a 12V SLA in parallel with your 12V power supply, if you just want time to get a generator setup or to stop it properly.

Post Mon Apr 10, 2017 11:05 pm 
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Nick
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That's not a bad idea - with another printer on the way a UPS that can keep them going for maybe 30 minutes would be peace of mind.
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Post Tue Apr 11, 2017 12:31 am 
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Knightrous
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Joined: 15 Jun 2004
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I'm surprised you do not have a Telsa Powerwall fitted to the work shop Razz
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Post Tue Apr 11, 2017 9:28 am 
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Nick
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Considering the monster $800 power bill for the last quarter, a Powerwall would make sense, The up-front cost for the solar cells puts me off though; the roof is shaded by trees for much of the day so it would take a large installation to supply the house.
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Post Tue Apr 11, 2017 11:11 am 
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pilleya



Joined: 31 Mar 2016
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Just spin Mr Mangle up-to speed using cheap off-peak power and draw power off of the eggbeater all day Smile

Post Tue Apr 11, 2017 9:24 pm 
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Valen
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lol that's a good call
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Post Wed Apr 12, 2017 9:05 am 
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Philip
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Location: Queensland near Brisbane


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quote:
Originally posted by Nick:
Considering the monster $800 power bill for the last quarter, a Powerwall would make sense, The up-front cost for the solar cells puts me off though; the roof is shaded by trees for much of the day so it would take a large installation to supply the house.
You might be allowed to clear trees to put in solar panels. Power will probably get more expensive and unreliable in the future making the case for alternatives more compelling.
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Post Sun Apr 16, 2017 10:46 am 
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Nick
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My local council are well known tree huggers; its almost impossible to have a tree cut down unless it is dangerously rotten. The main point for not cutting any tress is the cost; the last time it was over $5K Shocked .

Wheel testing:

I built a dodgy but reliable test jig to measure wheel grip and the results are interesting. Testing the actual load on Mr Mangle's wheels showed they have 3.9Kg on each one, so I loaded the jig up with the same weight:



With a fixed wheel in the arm, the test strip is pulled through and the force required measured on the scale. The Colson takes 3.5 to 4Kg while the first custom wheel takes 4 to 4.5Kg. That isn't as much of an increase as I hoped, but still 25% and testing is far from over.

The flexibility of the custom wheels might be too high; with the weight on the arm, it looks like this:



Having such a large contact patch might actually be decreasing the grip and the bot is more likely to scrape on the floor. I can always go back to a stiffer wheel rim and more testing.
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Post Mon Apr 17, 2017 4:24 pm 
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