Anyone know how to spin a blade fast enough using hand power?

[SeanAngelo]

So I have a project that I chose to do, which is a hand powered smoothie maker. Found that the ideal RPM for a blade to chop up the fruits is 21,000 RPM. But, how can I implement that into a hand powered smoothie maker?

 

How do you do the maths for it because I have no idea, I hate maths.

 

Does it need to be 21,000 RPM or can it be slower than that? Is 720 RPM enough?

 

Thanks in advance,

Sean.

[byalexandr]

It can be slower, but you want a sharp blade that still spins pretty fast. I would do some reduction gears so that the slow crank your hand puts in turns into a high speed (but low torque) rotation.

 

So a gear attached to the crank is very large compared to the gear attached to the blade itself. That way the speed is greatly increased at the cost of torque.

[Sauron]

You need gears. If you make a large gear spin by hand and connect a very small gear to it, the small gear will spin much faster than your hand. You just need to work out what the sizes must be to adapt your arm strength to the task.

[Joshua]

You'd need some serous gearing to get to 21,000 rpm by hand...

 

I agree. This is unfeasible.

[Interfectorem]

You're gonna need a pretty complicated gearbox to get 21K RPM out of hand power, even if you did, you'd need a lot of torque. If you're just cutting up fruits, I  don't think you'd need that much power, maybe just a hand crank with a gear or two.

[as96]

Gears, lots of gears.

[ZetZet]

It can be slower, but you want a sharp blade that still spins pretty fast. I would do some reduction gears so that the slow crank your hand puts in turns into a high speed (but low torque) rotation.

 

So a gear attached to the crank is very large compared to the gear attached to the blade itself. That way the speed is greatly increased at the cost of torque.

One gear won't cut it here, need to step down a ton.

[dalekphalm]

So I have a project that I chose to do, which is a hand powered smoothie maker. Found that the ideal RPM for a blade to chop up the fruits is 21,000 RPM. But, how can I implement that into a hand powered smoothie maker?

 

How do you do the maths for it because I have no idea, I hate maths.

 

Does it need to be 21,000 RPM or can it be slower than that? Is 720 RPM enough?

 

Thanks in advance,

Sean.

Question: Do you actually have to build this? Or is it all theoretical?

[SeanAngelo]

Question: Do you actually have to build this? Or is it all theoretical?

It's a project in college so yes, I need to build this but not a real one that's gonna be sold. Just a prototype so I can pass this class I just need it to work properly and show it actually does spin and such.

[SeanAngelo]

It can be slower, but you want a sharp blade that still spins pretty fast. I would do some reduction gears so that the slow crank your hand puts in turns into a high speed (but low torque) rotation.

 

So a gear attached to the crank is very large compared to the gear attached to the blade itself. That way the speed is greatly increased at the cost of torque.

 

 

You need gears. If you make a large gear spin by hand and connect a very small gear to it, the small gear will spin much faster than your hand. You just need to work out what the sizes must be to adapt your arm strength to the task.

Yeah, I already have a big gear and a small gear planned out but I just need the maths for it

 

I know having, say a 120 tooth gear and a 60 tooth gear, if I turn the 120 tooth gear once, the 60 tooth gear will turn twice.

 

So is 720 RPM enough to cut the fruits up to a smoothie drink?

[JebKerman]

you're going to need a massive gear for the handcrank side.

 

Assuming gears are based on teeth ratios (I don't actually know i haven't done mechanical engineering)

 

2100rpm is 350rps(econd)

so assuming you want to crank it at 1rps the handcrank gear needs 350 TIMES the teeth of the gear on the blade side

[SeanAngelo]

You'd need some serous gearing to get to 21,000 rpm by hand...

 

 

I agree. This is unfeasible.

 

 

You're gonna need a pretty complicated gearbox to get 21K RPM out of hand power, even if you did, you'd need a lot of torque. If you're just cutting up fruits, I  don't think you'd need that much power, maybe just a hand crank with a gear or two.

Well, I don't really want it to be 21k since I know that won't be done on hand.

 

So I'll just say it spins at 720-1000 RPM, what gears do I need? such as how many gears and how many tooth?

[werto165]

Considering I'm finding it hard enough to gear a wind turbine to get to 1800RPM on the generator I don't think this is possible with just your hand, this is a wind turbine going into winds of 40mph, that's using a MOD 1 16 tooth gear to a 48 tooth MOD 1 gear, effectively creating a 3:1 ratio, I think you can get pretty high gear ratios out of epicyclic gears but they cost a metric but tonne  

[rik1254]

The only way I can see this working is by implementing gears (like everyone else has said), so maybe a scrap bike with a 3+7 gear set up. Then you would need to go for more than enough blades to compensate for the lower RPM.

Go out and buy a hand whisk, assuming the whisks are sharp enough, maybe that would suffice for a good base to work from?

[SeanAngelo]

you're going to need a massive gear for the handcrank side.

 

Assuming gears are based on teeth ratios (I don't actually know i haven't done mechanical engineering)

 

2100rpm is 350rps(econd)

so assuming you want to crank it at 1rps the handcrank gear needs 350 TIMES the teeth of the gear on the blade side

hmm... 

 

so if I was to make it 720 RPM, that would be 12 RPS? Am I right?

 

So you'd need to spin the hand crank 12 times in a second? I don't think that's even possible....

 

Considering I'm finding it hard enough to gear a wind turbine to get to 1800RPM on the generator I don't think this is possible with just your hand, this is a wind turbine going into winds of 40mph, that's using a MOD 1 16 tooth gear to a 48 tooth MOD 1 gear, effectively creating a 3:1 ratio, I think you can get pretty high gear ratios out of epicyclic gears but they cost a metric but tonne  

So I'd need a big gear, medium gear and small gear in order to just achieve 720 RPM?

[ZetZet]

Well, I don't really want it to be 21k since I know that won't be done on hand.

 

So I'll just say it spins at 720-1000 RPM, what gears do I need? such as how many gears and how many tooth?

well say you can spin your handle once a second so you get 60 rpm there you need 35 gear ratio to get that up to 2100, you have 2.

 

 

if you have 120 tooth gear and 60 tooth gear you would need another 2 or 3 gears to get there.

[werto165]

hmm... 

 

so if I was to make it 720 RPM, that would be 12 RPS? Am I right?

 

So you'd need to spin the hand crank 12 times in a second? I don't think that's even possible....

 

So I'd need a big gear, medium gear and small gear in order to just achieve 720 RPM?

look on HPC gears if you want gears are pretty damn expensive man. 

[RollinLower]

maybe try using a setup with planetary gears? that'll be sure to speed things up. i mean, they use those things in pro-chargers!

[EvilLemur]

i dont think 720 rpm is anywhere near enough you would need more like 11,000 RPM to be efficient as the fruit will add resistance so touque will also be an issue as when you gear things you loose alot of energy if the ratios are far and apart. 

[SeanAngelo]

The only way I can see this working is by implementing gears (like everyone else has said), so maybe a scrap bike with a 3+7 gear set up. Then you would need to go for more than enough blades to compensate for the lower RPM.

Go out and buy a hand whisk, assuming the whisks are sharp enough, maybe that would suffice for a good base to work from?

I could use a hand whisk, take it apart and use a smaller gear for the big gear to drive.

 

Quickly did a search and found that they spin at 490-620 RPM, that's close enough for a 720 RPM goal

[Sauron]

Yeah, I already have a big gear and a small gear planned out but I just need the maths for it

 

I know having, say a 120 tooth gear and a 60 tooth gear, if I turn the 120 tooth gear once, the 60 tooth gear will turn twice.

 

So is 720 RPM enough to cut the fruits up to a smoothie drink?

 

generally speaking, the ratio between the teeth will be the ratio between the speeds. If you're turning a 60 teeth gear against a 30 teeth one at 100 rmp, the smaller gear will spin at 200 rpm. If you want 720 rpm and can spin your arm at 120 rpm, you'll need a ratio of 1 to 6. A 60 teeth and a 10 teeth for example. For 21k rmp you'd need a ratio of 175 to 1, not very feasible. Or, you could use a third weel that is actually a small weel attached to a large one and use that to increase the speed without using gigantic weels - bare in mind however that you also need to be strong enough to push that kind of rmp on the blade.

[Dimwitted]

You need a transmission box to do the ratios. Go the Barnacles Nerdgasm's site where he has a couple of projects similar to this that he printed. The MakerBot forums have quite a few similar projects.

[Bean86]

we used to have one of these when I was a kid.

https://img0.etsystatic.com/063/1/11036358/il_fullxfull.801498564_pqhm.jpg

https://upload.wikimedia.org/wikipedia/commons/9/96/VintageMixer.jpg

can't say if the force will be enouhg but if you get a 8 toothed gear on the cutter spindle the big round gear would need 96 teeth to get the 720rpm, assuming you'll manage 1 rps on the handle.

The math: 720rpm/60s=12rps so you'll want a ratio of 12:1 so whatever amount of teeth your small gear has multiplied by 12 is the amount of teeth the big gear needs.

The lowest you technically could go on the small gear is 6 but chances are high that contact angle would be at a limit and stress very high = skipping and/or breaking teeth.

Google 'vintage hand mixers' and you'll find plenty more pictures and designs.

this particular setup would be relatively simple to make yourself if you got access to a metal shop https://img1.etsystatic.com/000/0/5348283/il_fullxfull.337201265.jpg

The ratio on that one looks to be around 4:1 I guess (48:12 teeth) - so yeah you need a much bigger big wheel.

Alternative design idea is how corded salad spinners work

http://static.eatwell101.com/wp-content/uploads/2012/01/Signature-Salad-Spinner.jpg

you might want spend a little cash and get one or the other at a local store/fleemarket and see how they work up close.

Not sure if you'll be able to cut carrots or apples with it, some soft berries would be easier and yes get some very sharp blades.

[SeanAngelo]

we used to have one of these when I was a kid.

https://img0.etsystatic.com/063/1/11036358/il_fullxfull.801498564_pqhm.jpg

https://upload.wikimedia.org/wikipedia/commons/9/96/VintageMixer.jpg

can't say if the force will be enouhg but if you get a 8 toothed gear on the cutter spindle the big round gear would need 96 teeth to get the 720rpm, assuming you'll manage 1 rps on the handle.

The math: 720rpm/60s=12rps so you'll want a ratio of 12:1 so whatever amount of teeth your small gear has multiplied by 12 is the amount of teeth the big gear needs.

The lowest you technically could go on the small gear is 6 but chances are high that contact angle would be at a limit and stress very high = skipping and/or breaking teeth.

Google 'vintage hand mixers' and you'll find plenty more pictures and designs.

this particular setup would be relatively simple to make yourself if you got access to a metal shop https://img1.etsystatic.com/000/0/5348283/il_fullxfull.337201265.jpg

The ratio on that one looks to be around 4:1 I guess (48:12 teeth) - so yeah you need a much bigger big wheel.

Alternative design idea is how corded salad spinners work

http://static.eatwell101.com/wp-content/uploads/2012/01/Signature-Salad-Spinner.jpg

you might want spend a little cash and get one or the other at a local store/fleemarket and see how they work up close.

Not sure if you'll be able to cut carrots or apples with it, some soft berries would be easier and yes get some very sharp blades.

Wow, your post actually helped. Thank you so much!

 

Here's what I worked out based on your calculations:

 

At a ratio of 12:1 -

 

Say my small gear is a 20 tooth, so that means that - 

 

20 x 12 = 240

 

So I'd need a 240 tooth big gear acting as the hand crank gear and the 20 tooth as the blade spindle and that will get me 720rpm on the blade at 1rps on the hand crank?

Am I right?  :huh:

[byalexandr]

Yeah, I already have a big gear and a small gear planned out but I just need the maths for it

 

I know having, say a 120 tooth gear and a 60 tooth gear, if I turn the 120 tooth gear once, the 60 tooth gear will turn twice.

 

So is 720 RPM enough to cut the fruits up to a smoothie drink?

Not nearly enough. I would say at least 4000RPM.