10 tooth freewheel? (a little project)

[MitchJi]

Hi,

Good ole 6 or 7turn, 10 to 75tooth; seems 47-51mph realistic

Well, technically I still have a 3220 setup, driving a 3-speed Sturmy Archer hub that I got at http://www.utahtrikes.com, but this hasn't been ridden in over a year. In the brief time I used it, I had no problems at all, but this 3220 "direct drive" setup just makes way too much racket, for my tastes...

...I hate the direct drive setup I have now because it just makes such a horrible racket...

...The problem with trying to do a direct drive ratio of 8 or 9:1 is that the drive sprocket needs to be small and that means it will make a lot more racket...

...At some point I'm going to change my 11t motor sprocket to a 12t, which will bump the top speed in 1st to about 20 mph. This should also reduce the horrible racket my setup makes. That is the biggest problem with not having the belt drive 1st stage, it makes a horrible amount of noise, which is made worse by the small 11t sprocket...

...with the "direct drive" setup I did with the 3220 and the large #35 sprocket. That too sounded like somebody dumped a bucket of bolts into the spin cycle of a washing machine...

... due to the chordal effect. It is hard for a chain to get around a sprocket that has fewer than 11 or 12 teeth. It ends up sounding like bucket of bolts in a washing machine...

I think Matt found that a primary drive sprocket needs to be about 14t to be reasonably quiet.

 

[SoSauty]

Thanks Mitch,

Less expensive to relie on someone else's experience, so my enthusiasm is dampened. Yet the under the frame just in front of rear wheel motor mount would be bees knees for roadracing and the direct drive is sooo simple

My last thought, guess the motor performance suffers with low Kv and low 44.4V, so would you or anyone motor savvy care to venture a rough approximation as to Astro3220 8T 84Kv performance at 44V? If the rpm holds down to 3700, (read somewhere that this is almost a constant)
then:

6 : 1; 13 to 78tooth works out to a perfect 44mph for my 24" wheel.

Matt's fitting a little drive sprocket on FW has me debating a 3215 to fit into his belt drive or single stage drive a 3220.

This is my favorite setup so far, per dollar. There is some chain noise with that tiny sprocket. But, it is not too bad.

I see the need for quiet ride and prefer hub motors that don't alert country dogs for that reason. Yet for motored bike racing some noise would be good, or else the 2strokers wouldn't know you were coming up along side of 'em.

Can't wait to see how Matt inserts a slipper clutch into a belt pulley for his single stage drive, building a FW or slip clutch into a small drive sprocket does open up possibilities

 

[MitchJi]

Hi,

My last thought, guess the motor performance suffers with low Kv and low 44.4V, so would you or anyone motor savvy care to venture a rough approximation as to Astro3220 8T 84Kv performance at 44V? If the rpm holds down to 3700, (read somewhere that this is almost a constant)
then:...

kv is the no-load rpm per volt. For a rough calculation for gearing Miles recommends .85 so:
44v x84 x .85 = 3,142

Power is roughly proportional to RPM. Also the same motor wound for a higher rpm (lets say double) and geared down to 1/2 (same net rpm) will have twice the torque.

Another issue is high power draw at low rpm's kills esc's. Its not entirely coincidental that Gary popped his esc when starting from a standstill on his single stage bike.

This is my favorite setup so far, per dollar. There is some chain noise with that tiny sprocket. But, it is not too bad.

Thats because the small sprocket is the drive sprocket for the secondary reduction so the RPM is much lower than it would be on the motor sprocket. I think the primary reduction is 4:1.

Matt's fitting a little drive sprocket on FW has me debating a 3215 to fit into his belt drive or direct drive a 3220.

How did you arrive at those alternatives? A belt driven 3215 first stage system will be relatively quiet. A #25 chain driven 3220 first stage system using Matt's drive unit will only be a little noisier than a belt driven 3215 first stage system. A direct drive 3220 will be noisy.

IMO you should decide which motor you want (3210, 3215, or 3220) and figure out which 2 stage configuration best accommodates your needs.

 

[SoSauty]

Mitch,

I've read a good deal on the ES forum yet haven't any experience with the RC motors, (I'm starting my 1st build this week!) I'll start with a 3210 yet plan to start a 2nd build as soon as the 1st is tried out. Don't know if low gear on a 3210, 2 speed, will have the 22-33mph torque needed or if the 3220 would fry a controller if loaded at say, 22mph if single geared for 44mph. The .85 of Kv is a new bit of knowledge for me. So a 3220 7T would hit just under 3700rpm (44 X 97 X.85 = 3628rpm) :wink:

I was concerned my question would go unanswered and sincerely appreciate your response. When the 3210 arrives, I'll know lots lots more, such as how a FW and slip clutch are integrated. I still don't know the little Astros' capabilities but think I can get it to perform competitive enough to make the final race at Spooky Tooth. Maybe on the 2nd build I can use some of these ES examples to build a #40 sprocket around a slipper clutch or maybe I'll be infatuated with enhancing the little 3210 (under 25Kg/55lb race ready)

Guess I came up with the 2 possibilities because of my preference for low CG mounting (motor clears the ground 4.25" ). I think the single stage drive location behind the seat tube and between the crank arms, might allow a 2 speed, with 2 midsize rear sprockets, but not enough room for the 3220. The way low under the bracket direct drive location has room for the 3220 but chain path only allows 1 large rear sprocket.

 

[mud2005]

went searching again for large chainrings just for fun this was the biggest I could find w/o going custom.

it's 80t and 90 euros ($120), seems pretty good.

http://www.raptobike.nl/components/drivetrain/chainwheels/chainwheel-80t-ring.html

 

[recumpence]

Greespeed makes an 80 tooth as well. I just got one from them the other day. :wink:

Matt

 

[etard]

WOW Matt, those things go for a pretty penny, I'm surprised you haven't come up with your own custom sprockets complete with all the mounting options drilled in too.

 

[recumpence]

WOW Matt, those things go for a pretty penny, I'm surprised you haven't come up with your own custom sprockets complete with all the mounting options drilled in too.

:wink:

Matt

 

[MitchJi]

Hi,

went searching again for large chainrings just for fun this was the biggest I could find w/o going custom.

it's 80t and 90 euros ($120), seems pretty good.

http://www.raptobike.nl/components/drivetrain/chainwheels/chainwheel-80t-ring.html

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73t to 80t Standard - $67.50, Colored - $82.50, Hard Coated - $87.50
Above 80t Call or write

 

[mud2005]

this project inspired me to get more reduction in the final stage. I thought about using a 10t sprocket and copying matts design, but I instead went the simpler route and bought a larger chainring 80t and a smaller freewheel 13t.
it took 3 weeks to arrive from europe, but its here
party on

 

[boostjuice]

Link for the 80T sprocket please ?

 

[mud2005]

Link for the 80T sprocket please ?

oh yeah, http://www.raptobike.nl/components/drivetrain/chainwheels/chainwheel-80t-ring.html

 

[katou]

How large is that 80t sprocket? It looks big, but it's hard to know without something to compare with.

There is a calculator somewhere that will tell you how big a sprocket will be for a given # of teeth, anyone point it out?

Katou

 

[cargo]

not sure where the calculator is but it's a 1/2" pitch so:
80 x 12.7mm = 1016mm /pi
=323mm diameter about 12.5"