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Jolt & friends - Team Overkill - NSW
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MoonSet416



Joined: 25 Sep 2016
Posts: 436
Location: Sydney


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The new robot looks great. To my understanding there might be some slots randomly opening up at times.

Also, I wonder what gearboxes those are... They seem like bigger P60s.

Post Tue Jan 23, 2018 9:01 pm 
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Nick
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Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW


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They ARE larger P60s - its the Banebots P80 gearbox Smile I had to make quite a few modifications to make them fit.
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Post Tue Jan 23, 2018 11:06 pm 
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Nick
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The weapon pulley is taking shape; its a 76 by 30mm chunk of 7075 aluminium:



Its a simple looking part that needs really high accuracy. The slot to engage the end of the beater has to be lined up exactly with the pulley bore of the part will either not fit or be loose and rattle. Once its out of the mill it is extremely difficult to line it up again it the size is wrong.



The old pulley on the right was a good fit, let's see if I can fluke it again Smile. The new pulley a quite a bit heavier so its getting 12 holes drilled to remove about 50 grams.
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Post Wed Jan 24, 2018 10:38 am 
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Nick
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The pulley worked out almost perfectly; its a slightly loose fit but a piece of brass shim will fix it. Drilling the lightening holes was worth the effort; the new pulley is now only 9 grams heavier than the original.



Now its back to the electronics; once the power switch and a bit more wiring is finished, the bot can have a power-up test.
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Post Wed Jan 24, 2018 7:47 pm 
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maddox



Joined: 21 Dec 2006
Posts: 786
Location: Belgium


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You can get those 9 grams to, by chambering the pulley. Just keep enough meat for the shaft and the belt, the rest can be done with 8mm of ali.

Post Wed Jan 24, 2018 8:09 pm 
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Nick
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Joined: 16 Jun 2004
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I'm not too worried about saving weight - the spreadsheet says there is 1.16 Kg spare (for now...). I am hoping that all those holes rotating at high speed will resonate and change the beater's death hum into a full death howl - it might work Smile
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Post Wed Jan 24, 2018 9:47 pm 
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Nick
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From horizontal...

While the rotary table was set up, I drilled the bolt pattern on the new titanium motor shaft for Boom Stick - its only been on the to-do list for six months Rolling Eyes. The new shaft saves almost 70 grams and lets me put a pulley on the front of the motor instead of the back:



All assembled:



...to vertical

Back to the lightweight; the belt was too short so I had the reduce the pulley diameters. To do that, I first had to make a 32mm OD expanding mandrel to hold the pulley in the lathe:



Its a bit surprising the thick aluminium sections expanded at all but they did an excellent job holding the pulley:



The motor pulley is down to 36mm while the weapon pulley is now 71mm, The belt is now a good fit with a little slack to reduce shock to the motor:



That's OK for testing but a bit disappointing as the gear ratio is now below 2:1 and I wanted it closer to 2.5:1 for snappy acceleration and lower motor current - maybe its time to buy a longer belt.
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Post Sun Jan 28, 2018 6:07 pm 
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mark_m



Joined: 23 Apr 2005
Posts: 23
Location: Cambridge, uk


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good to see you building again Nick. I was getting withdrawal symptoms from missing your thread.

Post Mon Jan 29, 2018 11:48 pm 
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Nick
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Joined: 16 Jun 2004
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Thanks, more to come on both bots this week.
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Post Mon Jan 29, 2018 11:49 pm 
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Nick
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Boom Stick:

Everything screwed up today Sad. I started on the motor pulley, which runs a multi V belt and has a 16mm bore. The first mistake was drilling the bore, thinking that it would be anywhere near accurate; its just over 16mm at one end and .3 mm oversize at the other end so its a really loose & wobbly fit on the motor shaft.

The next problem was broaching the pulley. I don't have many metric broaches so using a 3/16" broach with a custom guide was the easiest option. Making the guide was a PITA; here is the 2nd attempt:



Getting the slot right took several goes; it turns out you can't just use a 3/16" end mill - who would have guessed? Laughing I also didn't have any spacers for the 2nd pass of the broach and had to improvise with cable ties, a handy trick when you lose the spacer on your swarf-covered floor. With the pulley done, I'm leaving the key slot on the motor shaft till tomorrow when the screw-up fairy has left the building.
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Post Tue Jan 30, 2018 8:58 pm 
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Nick
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No screw-ups today; probably because I bothered to look up all the key dimensions in Machinery's Handbook. The keyway was really quick to cut in the Ti shaft and now I can move on to the larger weapon pulley:



Once the bot design is finalised, I will cut the shaft to length an add a retaining screw at the end.
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Post Wed Jan 31, 2018 1:03 pm 
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Eidg



Joined: 27 Nov 2015
Posts: 10
Location: Switzerland


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Nice robot

About the bad weldings, thats exactly the reaseon why i manufacture most parts by myself. Luckly i do have some colleague which are working very precise.
Most suppliers are expensive, and don`t work accurate.

Post Fri Feb 02, 2018 3:32 am 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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Fuck-up fairies, part 2:

The step after finishing the out-runner shaft & pulley is to make a plate to hold the motor and bearing block for a spin-up test. I knocked up a 10mm thick plate using advanced paperCAM (trademarked):



Its a bit rough but the principle should work - EXCEPT the shaft in the bearing block is way too short. Seems I lengthened it in CAD but made it far too short to mount a pulley in real life Embarassed.



Rather than mess around, I went straight to making the final weapon shaft from titanium. This is how the bearings fit inside the bearing block.



Here is the business end with a multi V pulley cut directly into the shaft:



The next step is to cut a 1" by 8 pitch thread on the end of the shaft for a locking collar. That part has to wait until I get a larger thread cutting tool and learn to actually cut a thread on the lathe - its muh first time!
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Post Sat Feb 03, 2018 7:28 pm 
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Eidg



Joined: 27 Nov 2015
Posts: 10
Location: Switzerland


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Hello

Which 2 sizes of taper roller bearing are you using on the titanium shaft?

Post Mon Feb 05, 2018 5:05 am 
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Nick
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Location: Sydney, NSW


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The front bearing is a 30306 roller with a 30mm bore. the rear bearing is a 30204.
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Post Mon Feb 05, 2018 6:29 pm 
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