Direct-drive 3220 setup with a 3-Speed Hub...

GGoodrum

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I figured it was time for a new thread, so I could stop cluttering up others with bits and pieces on this direct-drive stuff. :roll: Anyway, what I'm doing is using an AstroFlight 7-turn 3220 (kV: 97) to directly drive a 3-speed hub on a 20-inch West Marine Port Runner folding bike. Normally, I would use a Shimano Nexus-3 hub, but I found a Sturmey-Archer SRF3 hub already laced into a nice 20" rim at UtahTrikes.com for a total of $49, so I decided to try one. So far, so good. It seems to shift as smooth as the Nexus, and it is almost exactly the same size, so I'm hoping the internals hold up as well. We'll see.

First, here's some pics:

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The drive part of this is really pretty simple. There's separate chains to the rear for the motor and for the pedals. Both rear sprockets are attached to the SRF-3 hub, via a standard Nexus 16T splined steel cog (also available at UtahTrikes.com...). I'm using a Nexus cog because they are dished slightly, which helps in the alignment of the chains. This steel cog is sandwiched between a 22T 4-hole 64mm BCD "granny gear" aluminum mountain bike sprocket, and a 94T aluminum #35 heavy duty go kart sprocket I got from gokartgalaxy.com. This sprocket already comes with a 2-1/8" hole and four holes in a compatible 64mm BCD pattern. The 16T cog lines up perfectly, so it literally just bolts together. I used some small 3/8" wide spacers I got from McMaster, to space the two sprockets apart a bit. This assembly then slides onto the splined hub and is held in place with the circlip. The big #35 sprocket is on the inside. The 22T sprocket ends up being perfectly aligned with the chainline coming from the crankset.

To keep the motor from driving the pedals, I replaced the front crank with an IPS crankset, which has an embedded freewheel. I'm having some adapters made, however, that will eliminate the need for having to add a FW to the crank. The adapter will replace the 22T sprocket with threads that will allow a standard BMX freewheel to be screwed onto the adapter. These come in sizes from 16T to 22T, so it will be easier to match a stock setup. Anyway, the adapters aren't quite ready yet, as my machinist guy needed to order a special bit to cut the fine-pitched 24 TPI threads, and I already had the IPS crankset and a 22T 64mm BCD sprocket, so I went with these to get this going.

The #35 sprockets and chain are much wider than even the 1/8" BMX chain/sprockets. I like this a lot. :) Very robust, and will certainly handle the power/torque the 3220 puts out. The finer pitch (3/8" vs 1/2"...) allows for higher ratios, which is really what makes this direct-drive setup possible. I'm currently using an 11T motor sprocket (also from McMaster...), which gives a reduction to the hub of 8.55:1. These 3-speed hubs have 1:1 ratios in 2nd gear, and about 1:0.75 in 1st. That bumps up the reduction is 1st to about 11.4:1. Third gear is like "overdrive", and has a reduction of 1:1.33. This ends up giving unloaded top speeds of about 22 mph in 1st, 29 mph in 2nd and 39 mph in 3rd.

I've only done a couple quick test runs so far, but I already know there's way too much power/torque in 1st. It literally threw me of the back the first time I goosed the power in 1st. The acceleration is pretty amazing, but you quickly run it up to the unloaded speed, in like a couple seconds. Even starting in 2nd, I can get the front end to pop up, if I give it too much juice. I was only hitting 90A/4kW peaks, but this motor has twice the torque of the 3210 on my other bike. Just like on my original Cyclone 1000W setup, I can't see needing to use 1st except if I'm stopped at the bottom of a steep hill. Anyway, I need to take another look at the gearing for this beast. I think I'll try a 14 or 15T motor sprocket.

Initially, I'm using the same 15s4p a123-based pack I've been using on the other bike, but I'm just finishing up a new 12s3p 45V/15Ah LiPo-based pack, made from six 20C 6s-5000 Turnigy packs from HobbyCity.com. This pack has a 12-channel LVC board, which uses the 3.0V TC54 voltage detectors on each channel, and has an active cutoff section that uses four IRFB4110 FETs to cut power if a cell hits the LVC point. I will also use this active cutoff feature with a small kill switch I'll mount somewhere. Anyway, I'm still finishing up the matching 12-channel Charge Balancer that will be used to keep the cells balanced during the charge process. For charging, I'm using a small Vicor 48V/4.5A power supply, with the output tweaked to 49.7V. The balancer is set so that each channel charges to 4.13V. This will increase the longevity of the cells.

The controller is a standard Phoenix HV110 with the PWM rate set to 16kHz and the timing left in "Normal", which means 5-10 degrees of advance. I also disable the current limiting and brake functions, and leave the auto-throttle mode enabled. I'm using a semi-custom version of Fecther's throttle board, without the current limiting function. This unit also has the equivalent of a Dimension SHV BEC, and it has four big 330uF caps, to aid the controller's ability to absorb the big spikes we see with ebike-type loads. The throttle is a half-twist hall-type that was used on this bike previously, when it had a Clyte 5303. Finally, I wired in a WattsUp meter, and attached it to the top.

The motor mount is simply an angled piece of 3" x 3" x 3/16" aluminum that attaches to a U-shaped "foot" that is welded to the bottom bracket tube. This is normally used as a "resting" spot for the bike folded up. Anyway, this "foot" is sandwiched between the angle piece and a flat 3"-wide plate. The motor mounts to the angled piece, as does the controller. There's just enough vertical play to allow for proper tensioning of the chain. One of the reasons I picked this bike to do the first direct-drive setup is because it doesn't have a bottom chainstay that would get in the way of the chain. For a more "normal" installation, which I will be doing next, I have a different mount which attaches to the downtube and is up against the bottom bracket tube, to control the torque rotation. This puts the motor right in front of the crankset. More about that later.

Today I need to put some "dimples" into the motor shaft for the moor sprocket setscrews. I have a couple of "flats" that I hand-filed onto the shaft, but this isn't enough to handle the torque of this setup, as the setscrews just can't hold for very long. I'm going to drill some dimples, like Matt does, which should do a better job of holding. Once I get this done, I'll do some more test runs. Unfortunately, there aren't too many hills here on Mission Bay, where I'm at this week, but I can still do some more acceleration tests, check the top speeds, and check the temps. In the few "blasts" I did initially, the motor never got above ambient (about 78F...) and the controller was only slightly warm to the touch. I've got my little temp sensor widget, though, so I'll do some more thorough checks later today. I'll try and get some basic video, if I can figure out how to strap my iPhone to the bike. :)

All-in-all, I'm very happy with this setup. The installation is a ton simpler, and the big #35 chain and sprockets are perfect for this application. The hub works great, although I really don't need 3-speeds on a 20" bike, I think. This motor actually has all six wires brought out, so I'm thinking I may try a left-side direct-drive setup, with delta-wye switching, on a future version.

-- Gary
 
Looks like fun Gary!!

With the circlip holding on the sprockets, how does the sprocket play stack up at the end of
the #35 sprocket. Do you get much wobble?

I'm glad to see you using an SRF3. It's be good to see how long it lasts vs. the Shimano,
especially with the big boy Astro. I'd like to make an outrunner equivalent of the 3220
by putting two HXT's together on one shaft, one shell, one stator, and a rewind.
 
There's really no detectable wobble. It is a pretty solid assembly. We'll see how it holds up, but the cog is steel, which is good.

Two HXTs would be a beast, for sure. :shock: That should be interesting, for sure.

The nice thing about the 3220 is it isn't too long. Everything can still fit between the pedals.

-- Gary
 
Alright!!

Looks good man..

The final gearing is just about identical between our setups....
but yours should be much more efficient.
 
Yes, I think this setup is going to be pretty efficient. I'm liking the #35 chain a lot. Very similar to D's #219 2nd-stage drive, but slightly larger pitch. Looks to be about the same width.

One other point I forgot about is that there's no freewheel on the motor drive, so pedaling does cause the motor to turn. I planned on this, because I eventually want to play around with regen, but the 3220 cogs a lot more than the 3210 did, so I might rethink this. I may look at putting a one-way bearing into a larger 14-15T sprocket, if I can find one that can handle the torque.

Miles, the frame is pretty beefy, which is another reason I like this bike for conversions, and uses a lot of square aluminum tubing. It is also pretty inexpensive, at $299, but they regularly have them on sale for $249. Time will tell, though. :)

I haven't pinged on Bob in a couple of weeks on the sensored versions yet. Time to bug him again. :roll:

-- Gary
 
Hi Gary,

Nice job :)

GGoodrum said:
I'm liking the #35 chain a lot. Very similar to D's #219 2nd-stage drive, but slightly larger pitch.

-- Gary

Why did you choose the slightly larger pitch #35? Sprocket availability?

How quiet is the DD with the 11T motor sprocket?

How hard/time consuming is it to fold and unfold the bike for travel?
 
This is the best setup I have seen for simplicity on quite a while. It is on par with friction drive for ease of installation! Great job, Man!

The only issue I can see apart from the lack of freewheeling is the lack of stealth. But, hey, my PK was not stealth, nor is my latest trike. :mrgreen:

I love it, Gary. Truely boiled down to just what is needed. :D

Fantastic.

Matt
 
MitchJi said:
Hi Gary,

Nice job :)

Thanks. :)

MitchJi said:
Why did you choose the slightly larger pitch #35? Sprocket availability?

Yes, motor sprocket availability actually. I originally bought some #219 sprockets, from one of the sites Miles found, but the motor sprockets that were available were all keyed and/or had tapered bores. McMaster.com has has lots of #35 sprockets, with regular straight bores. They have 3/8" bore "finished" motor sprockets from 9-13t, that fit right on the standard 32-series shaft, although the only 3/8" 12 and 13t sprockets they have are stainless steel, and cost about $50. :shock: That's why I started with an 11t.

MitchJi said:
How quiet is the DD with the 11T motor sprocket?

It is not too loud at all, quieter definitely than the 2-stage 3210 setup I have on my Dahon Mariner folding bike, for sure. Starting out, it might be slightly louder than D's setup, based on his video, but once going, it is surprisingly quiet.

MitchJi said:
How hard/time consuming is it to fold and unfold the bike for travel?

It still takes only 15 seconds to completely fold, or unfold this bike. Nothing I did adds to this. :)
 
Very nice Gary. This is very close to what I want to do with my mountain bike.

Ant Sync issues at all?
Can you go full throttle from a dead stop?
 
Looks pretty cool, nice job, very tidy! Glad to see someone else using those freakin huge 75A Andersons, I don't feel so weird now :D

I too am looking forward to the sensored 3210s when Bob gets around to making some. What is the max current draw for one of those things? I'm hoping my v3 ping will have enough oomph to do it justice so I don't need to reinvest in a new pack.
 
Really, really nice! It's very inspiring (and humbling) for us electrically-challenged guys out here. :D
 
Hi Gary,

very nice and clean :)
i'll be watching this thread with great interest, seems like the 3220 is a beasty, nice.
do you think a one way on the driveshaft will cut it? seems like a lot of torque? no doubt we need rc combined with great freewheeling to get the best of both worlds on our bikes?


D
 
This is beautiful. I love how you took advantage of the bike's lack of lower wheel stays so well.

It takes a lot of skills and a lot more thought to come up with something simple that performs well. The second version of my bike will be much more simple.

Any word on the progress of the dual freewheel adapters for rear hubs?
 
drewjet said:
Very nice Gary. This is very close to what I want to do with my mountain bike.

Ant Sync issues at all?
Can you go full throttle from a dead stop?

I have only seen a sync issue with trying to start off and run very slow in 2nd gear. I get some "chatter" if I try and go real slow. Doing this in 1st is fine, though. I haven't tried a full blast-off from a dead start yet, as I have a temporary chain interference problem, with the pedal chain. Originally, this bike had a dérailleur, so it has vertical dropouts. I used a singlespeed spring-loaded tensioner that works great, when pedaling. With the motor driving the wheel, the tension is in the wrong direction, and the chain ends up hitting the motor chain, occasionally. Once I move the freewheel out of the crankset, and to the back, using the new adapter, the bike chain will only move when you pedal, so I won't have the chain-slapping problem I have right now.

The first couple test adapters are done, but I'm down in SD this week, so I had to have my guy mail them to me. I should get them tomorrow.

-- Gary
 
deecanio said:
Hi Gary,

very nice and clean :)
i'll be watching this thread with great interest, seems like the 3220 is a beasty, nice.
do you think a one way on the driveshaft will cut it? seems like a lot of torque? no doubt we need rc combined with great freewheeling to get the best of both worlds on our bikes?


D

Hey D --''

I'm just starting to look for suitable oneways. I'll probably not get too far without Miles' help, though.

As for the stealthiness, the next one will definitely get some holes in the big sprocket. That should help. :) I'm also going to have my guy do a custom sprocket, if I can get Miles to help again with the drawings. :roll: :oops:

-- Gary
 
he's a bloody genius that Miles don't you know? :D
 
Miles is an awesome and handy guy to have around :)

I can vouch for that VBX bearing company. I've bought thousands of bucks of fully ceramic bearings from them for building reef aquarium equipment. They always get the bearings delivered in 2-3 days from when I place an order, and it's always been top quality parts the lowest prices.


What I'm jazzed about is that dual rear hub freewheel setup! That's going to be the evolution of RC motor E-bikes. The single stage reduction is also very slick. Less bearing friction, and much less loading on the final stage chain.

With that 3spd internally geared hub, the dual freewheels, and the sprocket mount for large diameter sprockets, Gary and Miles will have solved the biggest hurdles in an RC motor bike building, all in 1 simple elegant package at the rear wheel. Very cool stuff! And I am excited to be converting my own setup over to use a similar rear wheel setup on my own bike as soon as Gary ships me an adapter. :)

Keep up the great work guys!

-Luke
 
liveforphysics said:
With that 3spd internally geared hub, the dual freewheels, and the sprocket mount for large diameter sprockets, Gary and Miles will have solved the biggest hurdles in an RC motor bike building, all in 1 simple elegant package at the rear wheel.

Thanks Luke, but this solution is entirely of Gary's devising, I'm not due any credit for it.
 
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