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Ondray
Joined: 06 Jul 2015
Posts: 142
Location: Newcastle
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Feather making time.
I wanted a much simpler design this time, having a 3d printer now helps because I can print any tricky bits. So I went to my pile of volvo parts so see what I could use, and found this:
The radiator fan motor. Made in Canada no less! So the plan was to build a bot around using this motor, it doesn't have a gear reduction so that leads me to a KE spinner....The three wires on the motor and a quick play with it's control circuitry attached led me to believe it's was a brushless - but after I separated the wires and tried it on a 100A brushless controller I bought for it, I discovered it's brushed! Or at least it runs on DC. There's a red green and a black wire, the black is ground and it behaves the same regardless if I use the red or green, or both red and green wires...weird. But a bot bitz TZ85 runs it just fine. I just have a brushless ESC and no brushless motor now
I thought for a while about the easiest way to build a solid spinner, and wound up coming back to square section. But with the whole bot inside the tubes, and steel instead of aluminum this time. I put some designs on paper using the same dimensions as the Al in Hellamax (50mm sqr, 3mm wall) and came up with a steel shopping list including some 25mm sqr for Hellamax and some 50x10mm flat bar for a spinner...
...Turns out steel places only like to sell 6-8m long pieces! So my shopping list came out to over $200. I asked my old boss if he knew of any good places to buy steel and he said I could just grab what I wanted from his scrap pile on his property ...I didn't think he'd have anything thick enough for bot building - but I checked it out anyway and was happily wrong! Plenty of 75x50mm with 3mm wall, 40mm sqr and some other bits of angle. I also grabbed a tiny off cut of some 150x50mm stuff with a 5mm wall thinking it would be too big an heavy to grab the full bar - but it fits the 125mm wheels inside it perfect! This made armoring the wheels a jillion times easier (I was planning on building a box around them), which means I'll have to go back out to the scrap pile to get a bigger piece of the 150x75mm. Huzzah for scrap piles! Knowing the dimensions of what I was going to work with, I done up a design in Tinkercad:
So simple! most of the bot lives inside one piece of steel, a couple of bars to support the weapon motors and the 150mm pieces to protect the wheels. The design allows the spinning bar to be big, low to the ground and reach behind the bot as well. So somewhere between an offset horizontal bar and a full body. And if I line everything up carefully it will be invertible!
The design calls for some 3d printed pulleys and motor mounting brackets, I've been working on the brackets - up to my 3rd physical prototype:
It's a little big to fit in the section, I can sand them down - but it's all getting reprinted in ABS once I've built an enclosure so I've shaved the design 0.25mm in all directions. I think I'll add some side supports to fit into the 75mm section as well.
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Wed Jul 06, 2016 11:45 pm |
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Nick
Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
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Its hard to predict how that belt will perform - RPM, bar weight and even air resistance all play a factor. Based on using unreinforced Z urethane belt (about 5 x 10mm) on Mr Mangle, the round belt is probably going to stretch too much and overheat. Once it gets hot, it will start to stretch and that leads to a cascade of failure - trust me, I have seen it up close 'n personal!
If you make your own pulleys, perhaps you can make a dual pulley and use two belts?
If the printer's heated bed isn't getting hot enough, you can try insulating the underside of the heater mat. a couple of layers of corrugated cardboard should do the trick if there is nothing higher tech available. What died on the Bunnings heater, the element or the fan?
I have to agree about the Smallparts web site, its a shocker! _________________ Australian 2015 Featherweight champion
UK 2016 Gladiator champion
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Sun Jul 10, 2016 2:14 pm |
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