Sturmey Archer 3 speed torque and rotational velocity rating

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bigoilbob
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Sturmey Archer 3 speed torque and rotational velocity rating

Post by bigoilbob » Sep 21, 2017 2:19 pm

First off, sorry for asking about this on a thread for 5 speed hubs. I'll erase that post.

What are the actual, continuous duty, torque and rotational velocity ratings of the various Sturmey Archer 3 speed hubs? I've looked everywhere I can think of. Of course lots of "These are strong MF's", "NEVER use an IGH in a motorized build", and so on, in these and other fora, but nothing quantified. Say what you want about the NuVinci 171's (and yes, they are too heavy for non motorized bike builds), but they made this info available, and in it's proper context.

Thanks

The Speaker Guy
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Re: Sturmey Archer 3 speed torque and rotational velocity ra

Post by The Speaker Guy » Sep 28, 2017 1:21 am

Here's another non response response: I'm interested to know this too. I may change my four passenger trike to mid drive, and use SA3 at 3x rpm, hopefully to get 3x torque handling.

Make sense?

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amberwolf
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Re: Sturmey Archer 3 speed torque and rotational velocity ra

Post by amberwolf » Sep 28, 2017 3:20 am

Well, 3x rpm (at the rated torque) gets you 3x *power* handling, but it doesn't get you 3x torque. Not directly.

I suppose if it's a jackshaft rather than in a wheel, you could downgear at the other end to the wheel by 3x, to reduce the speed to 1/3 and re-multiply the torque by 3.

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Chalo
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Re: Sturmey Archer 3 speed torque and rotational velocity ra

Post by Chalo » Sep 28, 2017 3:47 am

I like to frame such questions in terms of the proven design parameters of the part in question. For a 3-speed hub, reckon that a 2:1 primary ratio is at the lower end of what was intended. Then reckon that a 250 pound rider standing on the end of a 7 inch crankarm and pulling up on the bars with a force of 50 pounds is foreseeable. So that's 250 lbs * 7/12 ft / 2 pounds-feet, or about 73 pounds-feet of torque at the hub input sprocket. Experience tells us that this level of torque works reliably for three speed hubs.

The hub doesn't care how fast it turns unless you spin it so fast under load that heat buildup becomes an issue. That's really, really fast. The things that break gearhubs are overtorque and misadjustment. Don't feed the thing superhuman torque and it will be fine, even if you're turning it at superhuman speed.
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bigoilbob
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Re: Sturmey Archer 3 speed torque and rotational velocity ra

Post by bigoilbob » Sep 28, 2017 8:52 am

Chalo wrote:I like to frame such questions in terms of the proven design parameters of the part in question. For a 3-speed hub, reckon that a 2:1 primary ratio is at the lower end of what was intended. Then reckon that a 250 pound rider standing on the end of a 7 inch crankarm and pulling up on the bars with a force of 50 pounds is foreseeable. So that's 250 lbs * 7/12 ft / 2 pounds-feet, or about 73 pounds-feet of torque at the hub input sprocket. Experience tells us that this level of torque works reliably for three speed hubs.

The hub doesn't care how fast it turns unless you spin it so fast under load that heat buildup becomes an issue. That's really, really fast. The things that break gearhubs are overtorque and misadjustment. Don't feed the thing superhuman torque and it will be fine, even if you're turning it at superhuman speed.
Thx Chalo, very thoughtful. I thought of this conceptually, but you did the arithmetic for me. If I figured out a way to MacGyver one directly onto my hub, the MOST torque I would apply would be ~55-60 ft.*lb, so that would work. That's 11 ft*lb from the motor, with 27/14 of it into my NV hub input, a 2/1 increase within the NV hub starting out, and a 60/44 increase from the hub output to the rear sprocket. I have this now, and can really winch with it. But, with my 8" (nominal) wheel, I might want to spin it at as much as ~550 r/m, on the output. Think that's too fast?

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Chalo
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Re: Sturmey Archer 3 speed torque and rotational velocity ra

Post by Chalo » Sep 28, 2017 1:53 pm

550 RPM is not a problem. That's like 26mph on a folding bike.
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Re: Sturmey Archer 3 speed torque and rotational velocity ra

Post by d8veh » Sep 29, 2017 3:01 am

Don't forget that you have to take the tension off the chain to change gear. That's not easy with some crank-drive systems because they run on a bit when you stop pedalling. I'd recommend a gear sensor.

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Re: Sturmey Archer 3 speed torque and rotational velocity ra

Post by bigoilbob » Sep 29, 2017 8:13 am

d8veh wrote:Don't forget that you have to take the tension off the chain to change gear. That's not easy with some crank-drive systems because they run on a bit when you stop pedalling. I'd recommend a gear sensor.
Thx d8veh, but if I could make this fantasy come true, then I would connect a simple 3 speed shift on my left handle bar, and throttle off to shift. Since my Nuvinci speed sensor is on my output, it would see less r/m, and would auto shift to my desired motor speed - ~350 r/m - automatically. What adds another layer of issue is that my disc brake is on my Nuvinci output. Showing my ignorance here - does a Sturmey Archer 3 speed come with a freewheel, or is it attached? I hope it is the latter, because I want it to both pull and push.

Sidebar, d8veh. Are you continuing to have good service from your Xiongdang 2 speed hub? Hope so. My front hub equipped, Bikee E2, tandem recumbent install worked well, until early summer. That's when I robbed the battery for the e mini bike set up that is in the link that you can trace to, from this thread. It's currently difficult to move the battery back and forth between builds (I'm gonna work on that), so my summer transport was my trusty ol' 650 Dakar.

Thx again for past and current help....
Last edited by bigoilbob on Sep 30, 2017 8:36 am, edited 1 time in total.

bigoilbob
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Re: Sturmey Archer 3 speed torque and rotational velocity ra

Post by bigoilbob » Sep 29, 2017 8:15 am

d8veh, FYI, here's the thread I started for the e mini bike that is the subject of THIS thread. It includes some pix, and some boring arithmetic.

https://endless-sphere.com/forums/viewt ... 12&t=89188

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