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Sand casting a robot chassis
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chunkulator



Joined: 27 Jul 2016
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Things are progressing with this design and I have some new CAD to post. However, I seem to have hit the limit of 10 photos in my personal forum gallery. What do I do about that then? Host them elsewhere? Or can some administrator please magic me a larger quota?

Post Tue Jan 24, 2017 9:41 pm 
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Philip
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You could upload them to http://photobucket.com/
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Post Wed Jan 25, 2017 1:38 am 
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Valen
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imgur.com is probably easier than photobucket and lets you directly link the images
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Post Wed Jan 25, 2017 10:19 am 
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Knightrous
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Dropbox and the public link is even easier.
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Post Wed Jan 25, 2017 12:09 pm 
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chunkulator



Joined: 27 Jul 2016
Posts: 211


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I have heard that the DropBox public link option recently became problematic because of the introduced traffic limit:
https://www.dropbox.com/en/help/4204

Seems like a dangerous option if we want the forum to keep working. Anyone ever hit that limit?

Post Wed Jan 25, 2017 9:06 pm 
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Valen
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I don't think we are going to be hitting 20gb or 100,000 hits a day here quite yet ;->
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Post Fri Jan 27, 2017 12:39 pm 
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chunkulator



Joined: 27 Jul 2016
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You say that now, but wait til the world gets a load of my CAD screenshots. This could be the "Charlie but my finger" of 2017!

Post Sat Jan 28, 2017 3:45 pm 
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chunkulator



Joined: 27 Jul 2016
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You say that now, but wait til the world gets a load of my CAD screenshots. This could be the "Charlie but my finger" of 2017!

Post Sat Jan 28, 2017 3:53 pm 
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chunkulator



Joined: 27 Jul 2016
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Drive systems

I have been assuming I'd use a BaneBots p60 drive system on this design but thought I should consider other alternatives as well. Doing the maths, a P60 plus motor plus a BotBitz 85A ESC costs about $A200 including shipping. This is a proven and reliable, yet somewhat expensive option.

Another option I thought would we worth considering is to use low kV brushless motors with a single stage of heavy duty spur gearing to give me around the same wheel speed. Maybe something like this:
https://hobbyking.com/en_us/kd-53-20-brushless-outrunner-195kv.html

Assuming "correct" no load wheel speed is around 20000 RPM at the motor through a 16:1 gearbox, that's 1250 RPM at the wheel. A 195 kV motor on 6S has a no load speed of around 4300 RPM so I'll need about 3.5:1 gearing. I can easily get about 4:1 with a single spur gear stage.

Chunky module 1 spur gears can be had on AliExpress for around $A10 and in fact I already have a range of them. Including TZ85As running SimonK this solution winds up costing around $A140 per side including shipping so is better from a money point of view and I'll be getting the potentially high power and efficiency of brushless. However I'll also be getting the uncertain startup and low speed performance of sensorless brushless, and I expect low speed manoeuvrability is going to be important for a ring spinner. Going Sensored brushless get's much more expensive, so that doesn't win.

What advice can people give me on the expensive brushed option vs the cheaper sensorless brushless option for a ring spinner?

Post Sun Feb 05, 2017 8:49 am 
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Nick
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In the UK, mini-moth uses very low KV motors like this: https://hobbyking.com/en_us/9235-100kv-turnigy-multistar-brushless-multi-rotor-motor.html



With a belt reduction rather than gears. Kain the builder added his own hall sensors to the motors and they worked very well. If that Keda motor you linked to has 14 poles, then you can use one of the Equals Zero Designs sensor boards: http://e0designs.com/products/hall-effect-sensor-board/ .
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Post Sun Feb 05, 2017 9:07 am 
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chunkulator



Joined: 27 Jul 2016
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Thanks Nick. I'll check out those aftermarket Hall effect sensors. Got any recommendations on Sensored ESCs? Haven't had much luck with cheap car ones.

Currently in Slaying Mantis I have some cheapish sensored car motors and cheap Hobbyking Xbeast Sensored ESCs, but I found that I couldn't get this configuration to run in reverse at full power. For one thing the ESC doesn't support changing direction, so I had to reverse two output wires and hack into the sensor cable to reverse two matching Hall effect sensors, but even after that the reversed motor only drove about half as fast as the non-reversed one. I tried playing with the mechanical timing adjustment on the back of the motor but couldn't fix it. i never really got to the bottom of that one, so I'm running that bot sensorless right now. Works great, but much higher kV and more gearing than I was considering for the ring spinner.

Post Sun Feb 05, 2017 11:10 am 
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Nick
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The VESC controllers are worth a look, several builders have used them with good results. When you are looking for a smaller car ESC, pick one that is designed for crawler trucks; they need to have full reverse with minimal delay and worked well for me for several years. Their main problem is being designed for low voltage (almost always 4S) and that limits their power handling and usefulness.

The sensored ESCs that I use wouldn't handle the current for those Keda motors but maybe the larger Castle creations ESCs will. Equals Zero is supposed to be developing a brushless ESC but its been delayed for quite a while now.
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Post Sun Feb 05, 2017 11:24 am 
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chunkulator



Joined: 27 Jul 2016
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Just sent my drawings out to quote on cutting the weapon from 16mm hardox and the body from 10mm 6061...

Post Wed Jun 28, 2017 1:16 pm 
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chunkulator



Joined: 27 Jul 2016
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Action Laser in Perth super responsive and quoted $100 for the hardox weapon ring + two snail cams I put in the void in the middle for Total Recoil 2. However, they don't do interstate shipping. How did you guys who've used them before handle getting the parts over to the east coast?

Post Wed Jun 28, 2017 5:59 pm 
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Glen
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Organise a courier to pick them up from action typically
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Post Wed Jun 28, 2017 6:14 pm 
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