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Warbros - Andre NSW
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Ondray



Joined: 06 Jul 2015
Posts: 139
Location: Newcastle


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Warbros - Andre NSW

I'll start my build thread with my first 'finished' bot Corpus:



Finishing involved adding a master switch, power light and a flail. It's pretty fail, but I've learned a lot.

Today I started playing with stuff to build a sportsman for vivid, here's the very rough layout (yet to be named):



Two ozito drill motors - the wheels were added today and two electric window motors from an old volvo (so indestructible). The plan is to use the low speed and high torque of the window motors to run some short lifter arms (which won't be shifters in the build). I wasn't initially thinking of making a wide bot, but after playing with the parts on the floor I think I like it, makes it harder to get around and keeps the center of gravity over the wheels and at the axis of the lifter arms. Plus I can add some thwack weapons on the sides. A pretty simple build, going to go with the rectangular section again I like working with it, but I may invest in some brazing equipment so the Al can hold itself together without the top and bottom. Biggest thing I'm pondering on at the moment is whether if or not to make the wheels bigger so it's invertable, the bunnings red wheels are 95mm and the window motors are 100mm, so going to the 125mm wheels would allow for invertiblity.

I was playing with arduino/esp8266 with some 30A ebay h-bridges with a grand plan of an xbox controller/tablet controlled bot. I haven't got very far. So now I think I'll save the headache for now and go with the RC equipment I bought to get started on corpus. Which is a nice easy to program turnigy transmitter and receiver plus some 10A crappy ebay speed controllers. The 10A speed controllers will definitely need to be upgraded to some at least 30A, probably going to go with botbitz (looking for advice there).

Otherwise I just need to get some polycarb, which is $240 for a 2.4mx.1.2mx6mm piece from the plastic shop down the road and some thicker Al section - thinking 4mm wall 50x50mm tube. I'll be spending Easter break with my Dad who's also keen for some building and has more tools than me, so I'll get started on the building then and have some more updates.

Post Sun Mar 20, 2016 9:59 pm 
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evil_steve



Joined: 06 Sep 2015
Posts: 301
Location: Adelaide, SA


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Wow, I'm impressed the 10A ebay ESCs didn't burn out in Corpus, that's what I'm using in most of my ants! Ive bought Botbitz 85A ESCs for my sportsman, probably overkill but I figured since I'm running two motors off each (including two lifting motors of unknown power) I'd rather be safe than sorry. I was thinking about getting a couple of the 30A ones for my simple wedgebot for Nationals though.

Post Mon Mar 21, 2016 7:29 am 
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Ondray



Joined: 06 Jul 2015
Posts: 139
Location: Newcastle


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So far I haven't done a full 3 min worth of driving with Corpus, but the tests so far haven't seen them get too hot. I use a rough method for calculating the stall current - I measure the internal resistance of the motor with a multimeter while it's stationary, in this case the little 12V air compressor motors on Corpus are a bit over an Ohm, I'm running a 2S lipo which is about 8V charged (which means the motors are way undervolted), I = V/R which is nice and easy for this, 8/1 so about 8 amps max draw, which the 10A controller can handle.

For the sportsman (I'm thinking of calling it Hellamax) the 12V ozito drill motor are about 0.5ohm and the window motors are about 1.8ohm, running off a 15V 4S lipo, so I'd need at least 30A for the drills and could maybe get away with a 10A controller for the lifters, but those basic 10A speed controllers I have only do 2S lipos so I still need the Botbitz 30A.

Post Mon Mar 21, 2016 9:33 pm 
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miles&Jules
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Joined: 19 May 2010
Posts: 3969
Location: ipswich QLD


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Awesome work - love seeing how first time builders solve problems👍-
everyone who is running brushed motors in feathrts use the botbitz tz85 they are very tough you can run em on 3 to 6 cell lipo and they last-so they are an investment- wanda has been tunnibg winches with the same set of tz85 for at least 4 years on 5s they just wont die😎 Looking foward to seeing your bots evolve🍕
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Post Mon Mar 21, 2016 10:50 pm 
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Valen
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Joined: 07 Jul 2004
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Location: Sydney


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small suggestion, measure the resistance of your multimeter leads, just short the leads and see if you get a 0 result, sometimes there is an offset in the meter that can give you wrong readings particularly at low resistance levels.
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Post Tue Mar 22, 2016 8:35 am 
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Ondray



Joined: 06 Jul 2015
Posts: 139
Location: Newcastle


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quote:
Originally posted by Valen:
small suggestion, measure the resistance of your multimeter leads, just short the leads and see if you get a 0 result, sometimes there is an offset in the meter that can give you wrong readings particularly at low resistance levels.


Yeah I left out the details, I usually measure a resistor of similar resistance first (so in this case a 1ohm) then chuck the motor in series so I'm measuring the change in resistance. But my multimeter does a pretty good zero so I get the same result either way.

And yeah I will probably get the tz85 based controllers down the track, I just had to buy 4 ESCs at once, so they were too much (even the 30A ones were a fair chunk for the 4) - the plan is to slowly upgrade to them.

Post Wed Mar 23, 2016 3:54 pm 
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Ondray



Joined: 06 Jul 2015
Posts: 139
Location: Newcastle


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End result of the long weekend. The frame is all cut out and the motors are in their brackets. It worked out real nicely with the 50mm Al Section, the window motors fit in snugly and are anchored with some locking nuts.

I wound up buying a drop saw after working up a decent sweat hacksawing the first test cut and realizing I had over a dozen cuts to go lol. It did make the cuts much more precise and made the angle cuts easy.

Next jobs are cutting the polycarb panels and bolting the frame together. I had some fun with a jigsaw trying to cut the polycarb. The guys at the plastic shop told me to use a fine tooth blade, so I used one of the finer toothed blade in my set...It melted the polycarb more than it cut and the cut literally healed itself. So I tried a coarser tooth blade and it was going well until it bent because it was cheap poop. So while I was at the hardware store I bought what I thought were some decent jigsaw blades (the guy even told me they should work) but the teeth pointed the wrong way which made the jigsaw jump up in a scary fashion...so that's been deferred until I get the right blade.

Joining the frame is an area I'm still pondering on, the current plan is to bolt it all together with steel L-brackets and self tapping screws, with added strength from the polycarb being bolted on top and bottom. I feel as though this will be strong enough but I'm still investigating welding or brazing the frame together. I did buy a propane torch and some little brazing rods to give it a go, but this Al sucks the heat away too quick.

Post Tue Mar 29, 2016 10:06 pm 
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marto
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Joined: 08 Jul 2004
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Location: Brisbane, QLD


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Polycarb really tends to crack when cut and drilled. Why not chopping board (hdpe).


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Post Wed Mar 30, 2016 10:11 am 
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Ondray



Joined: 06 Jul 2015
Posts: 139
Location: Newcastle


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Because polycarb is transparent and the plan is to polish the Al to give it a nice chrome shine.

It's 6mm thick and the test pieces I've been playing with haven't had any trouble with regards to cracking. We'll see, I used chopping board for the first bot but I've bought so much polycarb I'm pretty much committed.

Post Wed Mar 30, 2016 4:33 pm 
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maddox



Joined: 21 Dec 2006
Posts: 779
Location: Belgium


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I garanty you, the Polycarb will crack.
6mm Polycarb is like a flyscreen for a high power feather.

6mm PC= 9mm HDPE

Post Wed Mar 30, 2016 5:56 pm 
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evil_steve



Joined: 06 Sep 2015
Posts: 301
Location: Adelaide, SA


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Love the way you've shaped the frame. Are you planning on supporting the drives at the gearboxes as well as the motors?

Post Wed Mar 30, 2016 9:14 pm 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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@ Mario: I think this is for the Sportsman competition, so polycarb is probably fine.

When cutting polycarb, I either set the jig saw on it's lowest speed or I push the saw thru the material crazy fast to prevent heat build-up. The fine tooth metal blades will leave a neat cut but only at low speed. The medium coarse blades meant for thin wood are the best all-rounders for thermoplastics in my experience.

To lower the chance of cracks, make all inside corners (IE around wheel wells) rounded to prevent stress buildup.
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Post Wed Mar 30, 2016 10:23 pm 
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Ondray



Joined: 06 Jul 2015
Posts: 139
Location: Newcastle


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Well on this advice for the polycarb I'll be making sure all the internals are mounted to the frame and not the base panel! Shouldn't be too hard, then even if the polycarb does fail everything will still stay put. I was thinking of putting the battery and ESC's in their own Al section's inside the bot anyway.

Steve, the plan for the wheels is to run an additional smaller bit of Al section holding a bearing to support the shaft where it comes out of the gearbox. Which reminds me that I need to order those!

Nick, thanks for that advice on the rounding, I will do that. Otherwise I was going to cut the squarest holes possible for neatness. I know which jigsaw blade to get, the one that jumped around all scary left a real nice cut when I put all my weight on the jigsaw, just need to get it with the teeth pointing the right way (I don't even know why you'd want the teeth to point out).

Post Wed Mar 30, 2016 10:32 pm 
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evil_steve



Joined: 06 Sep 2015
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Location: Adelaide, SA


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I ordered these bearings off of eBay which fit the drill shafts perfectly, but took about 4 weeks to get here.

Post Thu Mar 31, 2016 6:58 am 
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Ondray



Joined: 06 Jul 2015
Posts: 139
Location: Newcastle


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My impatience meant I ordered some ebay bearings from an aussie seller, just couldn't get flanged ones.

I got my ESC's on Friday and had a chance to play with the electronics setup tonight: (caution - it's messy)



Two problems have been identified:

- I don't have any wire of sufficient gauge to handle the current between the battery and the speed controllers. The thin wire on my alligator clip cords got hot quick...

This has been rectified by ordering some 10AWG 3.7m booster cables off supercheaps ebay store for $10 - good bargain. I probably could have scabbed around the tip or council cleanup but anyway...


- My transmitter only has 3 mix's, and my current method of mixing requires 4. It doesn't render the setup unusable, it just means I can only operate one lifting arm independently.

The plan was to have the arms operate like the wheels do for skid steering, stick up/down they go the same way, left/right they go opposite directions.

I'm using a Turnigy TGY-i6 AFHDS 6CH transmitter/receiver. For the wheels I'm mixing channel 1 and channel 2, channel 2 is up/down on the right stick and channel 1 is left/right. I use one mix make channel 1 slave off channel 2 so the wheels go the same direction for the up/down. I then use a second mix to slave channel 2 off channel 1 but in reverse, which generates the turning.

To do this for the lifter arms as well I'd need 4 mix's operating the arms off channels 3 and 4...

...I feel as though there's an elegant solution to this problem, that I'll probably come up with at about 3 am and forget by morning if I don't write it down.

Post Mon Apr 04, 2016 11:20 pm 
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