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 Mounting Spinning Blade to 1/8" shaft

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Ryan McKinney



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PostSubject: Mounting Spinning Blade to 1/8" shaft   Wed Jul 21, 2010 11:05 pm

I'm making an ant weight with a vertical spinning blade and I need a way to mount the 1/8" thick tool steel blade to a 1/8" diameter steel shaft. I figured welding was out of the question because the shaft was too thin. Would it work if I attached a collar to the shaft next to the blade, drilled a couple holes through it and the blade, and then held the blade to the collar with a couple pins or bolts? And if I did use a collar, would a set screw collar work better, or a clamping collar? I'm not really sure how I'd use a keyed shaft...
Any better ideas would be appreciated.
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Cody
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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Wed Jul 21, 2010 11:13 pm

ever think of making a dead shaft and putting bearings/bushings in the weapon?
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Jeff L
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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Wed Jul 21, 2010 11:15 pm

Cody Harris wrote:
ever think of making a dead shaft and putting bearings/bushings in the weapon?
^Do this.

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Ryan McKinney



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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Wed Jul 21, 2010 11:32 pm

What's a dead shaft?
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rjw
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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Wed Jul 21, 2010 11:34 pm

a shaft that does not spin


Consider using a larger diameter shaft. If weight is an issue, a hollow one

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Cody
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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Wed Jul 21, 2010 11:49 pm

maybe jeff or dan could recomend some bearings/bushing and a good shaft size?
Im sure rjw even could they just have experience with wittlle bots
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Dan Curhan
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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Wed Jul 21, 2010 11:59 pm

I highly recommend a dead shaft. But if you insist on a spinning shaft, 1/8" steel is going to bend. Period. Your antweight will not survive with an 1/8" steel shaft.

But theoretically, a shaft collar with holes through it bolted to the blade would work. And at 1/8" I'd use a set screw collar, so you can really dig in with the set screw. I'd even file/grind a small flat on the shaft to tighten the set screw against. I wouldn't trust an 1/8" clamp collar to hold tightly enough...

My advice - go with a 3/8" 7075 aluminum dead shaft. You'll thank me.

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Ryan McKinney



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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Thu Jul 22, 2010 12:20 am

I'll definitely go with a dead shaft then. Is it necessary for the dead shaft to be completely still, or could it just sit in its aluminum supports? For that 3/8" aluminum dead shaft, would it have to be solid or could I use a hollow one? The shaft is only going to be about 1 - 1.25" long btw.
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Cody
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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Thu Jul 22, 2010 6:16 pm

we always ran a screw through the support rail and the shaft
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Ryan McKinney



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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Fri Jul 23, 2010 11:39 pm

Ok I'll do that. Change of subject: Would this battery http://www.robotmarketplace.com/products/LP-TP480-3SJPL2.html work to power this motor http://www.robotmarketplace.com/products/0-EFLM1105.html or is the discharge of the battery not enough? If it isn't, how about this motor instead: http://www.robotmarketplace.com/products/0-EFLM1010.html
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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Sun Jul 25, 2010 1:14 am

go with the thunder power G4 45C discharge series. They're awesome. Tiny, light, and super powerful.

As far as motors go... that first motor you linked to? Do you know what kv means? Especially 3700 kv? That means that for every volt you give this motor, it'll spin 3700 rpm. Your battery was 11.1V, so that comes out to over 40,000 RPM. I hope you're planning on gearing it down a lot, or have an otherwise clever plan to use such high rpms...

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Ryan McKinney



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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Sun Jul 25, 2010 1:50 am

I need to use a battery that weighs about 1.5 oz. It appears that the thunder power g4 45c series only comes in either a 325mAH or 850mAH that would be within my weight limit. The 7.4 volt 850 mAH is about perfect on weight, but do you think it would last for 2-3 minutes, the two drive motors being copal 60:1's ( http://www.robotmarketplace.com/products/0-COPAL60.html ) and the weapon motor being that 3700 kv E-flite Park 400 inrunner?

Edit: Why would I want a 45c battery instead of a 30c one if 30c can give 25A continuously and the brushless motor only needs 15A?

And yeah kv is one of the few things I actually do sort of know about haha. I just figured the weight of the blade would slow it down a bit, and the gear ratio between the timing pulleys is 2.8:1. Since the battery that I might use is only 7.4 volts that should help to lessen the rpms to around 10k.

I got the info on the batteries here: http://thunderpowerrc.com/PDF/ThunderPowerRC-Pricing.pdf#page=3
I'm sure you could already tell, but I'm new to this stuff. I didn't really learn anything from PV engineering club

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Cody
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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Sun Jul 25, 2010 12:27 pm

how many amp burst?
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Ryan McKinney



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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Sun Jul 25, 2010 5:04 pm

The maximum burst current used by the brushless motor is 20A. The 30c battery can give a burst up to 51A and the 45c up to 76A.
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Dan Curhan
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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Tue Jul 27, 2010 7:03 pm

a pine view kid that sorta knows something! I'm so proud... haha

anyways the thunderpower g4 45c series is just what i use. It's a smaller, lighter battery with more "oomf" but if the other is adequate for what you need, then there's really no compelling reason to use it.

I will warn you (since I work as one of the "tech guys" at robot marketplace) that the COPAL 30 and 60:1 motors have a plastic first stage in the gearbox to reduce noise. The 50:1s have all metal gears. The 6V version can be run over 12V fine, so if you like the copal size, that would be my recommendation. Protecting the exposed gears is pretty easy, so I wouldn't worry too much about that.

10k is a pretty good speed range, but make sure the blade really bites, otherwise you won't get any big hits in.

Are you gonna have this ready by August 14th? Robot Marketplace is having an insect event and you should come, even if you just watch.


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Ryan McKinney



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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Tue Jul 27, 2010 10:39 pm

I've decided not to use the Copal 60:1 motors even though I already bought them. I guess I'll have to pay the restocking fee but whatever. I'm going to use either of these to save weight. I'm not sure which one yet though:
http://www.robotmarketplace.com/products/0-GM11A.html
http://www.robotmarketplace.com/products/IL-SAN50.html
They seem a bit small, but as long as they can drive my bot and last for a little while, I'll be happy with the 20-30 grams of saved weight.

I think the blade design should allow it to bite pretty well. The blade is a 6" bar curved a bit in opposite directions at either end. I was hoping that might help it bite more but if nothing else, it looks cooler.

I might make it to the Robot Marketplace event. It'll be close, depending on how long it takes the battery to ship.

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Ryan McKinney



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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Wed Jul 28, 2010 9:11 pm

Dan, seeing as how you used to live in Sarasota, do you know where I can get .25" diameter UHMW round rod locally? I would get it from onlinemetals.com but the shipping costs are like 10 times the cost of the UHMW. I just ordered something and forgot to add the UHMW to the order, so I'd rather not pay for shipping again
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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Wed Jul 28, 2010 11:37 pm

Ryan, I'm still in Sarasota for summers/breaks. Just sayin.

For quarter inch UHMW? I don't think there's any place local that would have it. Alro metals on 12th street just west of US301 has a ton of good stuff, but I doubt they'd have anything plastic that small. They're mostly metals.

I would try McMaster-Carr before online metals for something like that...

Those little motors should be fine. You can't get the 50:1 in-store, but we have the 56:1s in stock. I used those in Conundrum. They're a little slow at 2S, but I'm sure you'll figure something out. We're about to get a bunch of new motors of that same form factor that are better than anything we currently have. It's gonna be about 3-4 weeks, but you may want to upgrade at some point after seeing the performance differences. I upgraded Conundrum and Shred to some of these new ones and they were much better.




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Ryan McKinney



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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Mon Aug 02, 2010 4:51 pm

Oh ok. Well you know the area even better then. I think I'll order it from Mcmaster, or just use Aluminum if I can spare the weight.

I'll probably upgrade and then keep the other two as backups. I'm not that worried about the motors going slow, as long as they work. Form factor? What does that mean?
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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Wed Aug 04, 2010 9:29 pm

by form factor I mean size. Those little motors are basically 10mm x 12mm with a 3mm shaft. That's what I mean by form factor. The length of the motor depends on the motor that's attached to the gearbox, but it's usually anywhere from 24mm to 35mm.

There are lots of companies that make this style/size motor:
-Solarbotics
-Pololu
-TT Motor
-Sanyo
...etc.

but they're all very similar. The pololu mounting brackets (0-PL1089 and 0-PL989) will fit any brand as long as it's the same form factor - ie 10mm x 12mm gearbox with a 3mm shaft.


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Ryan McKinney



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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Thu Aug 12, 2010 4:07 pm

Ok thanks for clearing that up. Upgrading should be pretty simple.

I'm trying to figure out the best way to mount a 3 mm bore timing pulley to the 2 mm shaft of my brushless motor. Should I grind a flat surface onto the shaft to tighten the set screw against, or just put in the set screw against the round shaft?
Would it be a bad idea to just use some tape to make up for the 1 mm space, and then put in two set screws on opposite sides so it doesn't slip?
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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Thu Aug 12, 2010 8:39 pm

To cover that gap, the proper way would be to try and make a round shim from some metal (AL maybe?) to take up the slack.

Now the improper ways require more creativity Smile

In the past, I have used Anti-static tape with a rubberized glue to make the shim. It might take a few tries so be careful with the motor.

Because 1mm is really too small to make a good shim (.5mm wall WTF?!), I would try and do this instead. I would bore out the pulley and make a shim then. Because the pulley has a larger ID now, the task is far more feasible than before.

What you should not do is screw the pulley onto the motor shaft, thinking the gap is no big deal. There will be vibrations, your set screw will loosen, and your weapon pulley will fall off and possibly damage your motor. Not worth it at all.
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Ryan McKinney



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PostSubject: Re: Mounting Spinning Blade to 1/8" shaft   Thu Aug 12, 2010 11:43 pm

Ah ok a shim sounds a lot more reliable than tape. So could I just press fit the aluminum shim onto the shaft and tighten the set screws into the shim? Or would it be necessary to have the set screws go through the shim to the shaft?

I'll probably just bore out the pulley to 1/4" and then drill a 2mm hole in a short piece of 1/4" aluminum rod to make the shim.
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