Engineers, I Need Your Help! (Gear Ratio / Pitch Diameter Question) - General

I've got an Engineering project and we're trying to get two gears to fit together. Basically, we're building a Horizontal Axis Wind Turbine, and we're going to have these two gears ([URL="http://uk.rs-online.com/web/p/spur-gears/5216193/"]this [/URL]and [URL="http://uk.rs-online.com/web/p/spur-gears/5217174/"]this[/URL]) in our assembly. Would they work together? The setup is going to be the big gear on our blade shaft (the one that spins from the wind), and the small gear will be connected to our generator shaft, to hopefully get that shaft to spin much faster and produce more energy. I have no idea how pitch diameter works, but I feel like those gears won't match up and they'll just grind against each other. Also, would it be a smart idea to have both gears made of metal, instead of one metal (harder material) and one plastic (softer material) to avoid excessive wear and tear? I'm worried at high RPMs, the plastic teeth will just get shredded.

Hi, Why did you chose those two gears ? What generator and turbine are you using ?

[QUOTE=426_Hemi;49251624]Hi, Why did you chose those two gears ? What generator and turbine are you using ?[/QUOTE] It's a self-built turbine, we're building it from the ground up. We chose these two gears for their bore diameter, since the shafts in our turbine are 6mm diameter as well, so it's easy fitting. Also, we chose the gears to give a 5:1 ratio (I think that's the ratio they give??). The generator we're using is this: [QUOTE][IMG]https://i.gyazo.com/f0f1a74da4ded7d07a6a85fda08e5685.png[/IMG][/QUOTE] [editline]5th December 2015[/editline] Irrelevant question, does "Total Size : 20 x 25mm / 0.8" x 1"(D*H)" mean the component (in this case, a coupling) is 20mm long and 25mm high AKA 25mm diameter?

Yeah that seems about right, I stupidly thought it was depth and height.

If it were me I would probably just use both metal gears rather than one metal and one plastic

I'll do that, then. Main question is whether or not these gears will mesh together or not. If not, what am I actually meant to look at to ensure gears mesh? I don't get any of this pitch diameter shit.

Hey OP, I just finished my third year engineering where we had to design a 2 speed gearbox with all the shizles needed to make the thing tick. If your gears are designed properly, the teeth roll over each other and there's no "wear". This is because of the involute shape of the teeth. They basically make sure the contact between teeth is always normal to the surface (IE no shear or friction component). So make them the same material if you can since you'll want as big a safety factor on your gears as possible. I may be persuaded to show you how to do the safety factors on the gears after Monday since I'm writing an exam on Control Systems I will look at the gears you sent and do some math to check they mesh properly. I'll post my reply below soon. ------------------------------- Ok, so they're spur gears with involute teeth. What matters now is whether their modulus is the same. The gear modulus is how many teeth there are per unit diameter. So for the big one we have: (30mm pitch/ 60 teeth) = 2 For the small one we have: (12mm pitch/12 teeth) = 1 This means these gears won't mesh. You need to find gears with matching moduli and since you'll be subjecting them to some shock loads with lots of variations in the running cycle I'd definitely make them both metal. To make sure you don't have surface wear you also need a little more than one tooth in contact between the two gears when they mesh which means as the one disengages there's already a new one to take the force and the next pair of teeth won't smack into each other. If the project does not require this much detail then don't worry, but I'll help if you want

I really appreciate you taking the time to write all that. I figured out the gears wouldn't mesh yesterday (because of the differing moduli) but your in-depth post has really helped a lot. If it's just a First Year project, is it necessary to buy two metal gears? We have a small budget and I'm only really finding metal gears for 5 quid or more, which is quite hefty! I was hoping two plastic gears would do the job, seeing as we literally just need it to run once and pass the wind tunnel test. Right now I'm searching for gears that'll give a 2:1 or 5:1 ratio, but it's super hard finding them of the same modulus and material.

I think I can build something to surpass those metal gears.

[QUOTE=Yahnich;49257779]if your uni's fablab has 3d printers you coul design them yourself[/QUOTE] Unless it's an SLS or extremely high end SLA printer, don't bother. 3D printing gears with an FDM printer for any kind of durability sensitive usage is asking for trouble. ABS can kinda do it but you're still spending a lot of time filing teeth to make it happy. The problem is the ridges that are a byproduct of layer based extrusion tend to cause excess wear, even in non-shear/friction gear pairs. So if you do print the gears in ABS you'd need to give it an acetone treatment for smoothness which would likely end up with uneven teeth causing lots of wear and thus making it all pointless.

[QUOTE=Yahnich;49257779]if your uni's fablab has 3d printers you coul design them yourself[/QUOTE] There's tonnes of restrictions and loopholes we gotta jump through to get our stuff approved to be printed in the 3D printer. Way too much effort. First year is pretty prohibitive when it comes to giving us the responsibility and trust to use the big boy machines. I ended up finding two perfect gears that mesh together well, so all is good! [editline]6th December 2015[/editline] Yeah it's not exactly a prototype, but we only really have the one main test it has to go through, plus a few earlier tests to spot any problems with it. So I'd say max, it has to withstand the wind tunnel 3 or maybe 4 times. Groups from last year had their turbines tested until failure, as they kept trying to push it to it's limit to get the most power out of the generator. Had gears getting ground down and blades snapping and constructions falling apart from the stresses of repeated testing. My aim is just to get it to work a few times.