The Linear (recumbent) Booster

[johnrobholmes]

Nice! That looks rather beefy.

[lawsonuw]

Got the magnets for my new field in yesterday. Started gluing them in. The five silly magnets for each pole didn't like sitting next to each other! I had to glue them down in two batches. First the center and two outside magnets. (using a spare magnet to get the spacing right) Only after the glue had set for those magnets could I glue down the last two. Also, I'm glad my magnets were small. I'd have several shattered magnets by now otherwise. And even these small magnets are a pain to get apart.

Also, I've got the motor running on 12v right now. The output of the transmission clocks in at 76.4 rpm. So about 1471 rpm at the motor. 1471rpm/12v gives me a ballpark Kv of 123 rpm/v. Factoring in the .6A idle current and 4.5 ohm terminal resistance a better estimate of the Kv is 158. Good news is with my current gearing I'll only need about 35-41v to match the motor's free speed to a 100-110rpm cadence. (34T on the crank 13T on the gearbox) Bad news is that due to the internal resistance of the motor and brushes, I'll be hard pressed to get more than 100w out of the motor at this voltage. (each brush has almost 1 ohm each!)

Back to plan A, I'll be putting in an order soon for parts.

Marty

Edit: Just hooked it up to the 30 cell NiCd on my Trek. (currently at 38v) and it spins at about 200 rpm and draws about 0.7 amps of idle current. Yes, this motor now cogs a LOT.

[etard]

You know the 36 volt drills put out around 600 in/lb torque, that seems to be enough for our application. has anybody thought about using a dewalt or other drill to power thier bike? I live in a dry climate, so I was thinking about using one with plug n play batteries in a friction type drive. I could use the trigger as my throttle, and just use all the internals of the drill. Or would the gearing of the drill make it more suited for a Curry type of drive? Does anybody see any problems with this logic?

[lawsonuw]

No problem with your logic Etard. Cordless drills make pretty good gear motors. The battle bot community often uses drill gears and motors for drive. Drills often spin 500rpm or less in low gear, which with one chain stage can be geared to the pedals, or directly to the rear wheel. They do make a bit of noise though.

Anywho, Just pulled the trigger on a bunch of parts. For this machine I ordered This cheap motor. It's a bit slower than I'd like, but a new freewheel or a few more cells will fix that easily. I also ordered 2x P# A 7C55MPSS1906 and 1x P# S40PX0MHG6M-130 from http://www.sdp-si.com. I'll replace the motor's shaft with these and set it in the same spot as the original armature. I'll also have to build up the OD of the front bearing to 22mm to make it fit, and provide a torque arm for the motor.

Marty

P.S. I also bought a bunch of parts for my 1lb battle bot Micro Vice. Check out an old version of it over HERE on YouTube.

[michaelplogue]

You know the 36 volt drills put out around 600 in/lb torque, that seems to be enough for our application. has anybody thought about using a dewalt or other drill to power thier bike? I live in a dry climate, so I was thinking about using one with plug n play batteries in a friction type drive. I could use the trigger as my throttle, and just use all the internals of the drill. Or would the gearing of the drill make it more suited for a Curry type of drive? Does anybody see any problems with this logic?

A bit pricy, but........

http://www.dpxsystems.com/ProductDetail.aspx?ID=199

http://www.dpxsystems.com/PDFs/DPX%20Web%20PDF%201.pdf

[lawsonuw]

Finally got my motor. (PayPal took it's bloody time...) I'll have some more pictures up tomorrow.

Marty

[lawsonuw]

The two pictures show how I'm mounting the new motor in the drill. Still needed is a torque arm for the front of the motor, an exit hole for the motor wires, and to remove some plastic that's rubbing on the motor.

I also took a bunch of measurements from my motor.

Code: Select all

Rm: 0.047 [ohm] measured between any two phase wires
Advance     Kv [rpm/v]    Io [amp]     Vbat [volt]
4-10        348           1.05         12.8
10-20       366           1.16         12.6
20-30       376           1.30         12.6

Some flux is leaking out of the motor can, connectors were not included, the motor is well balanced this time, 12 stator teeth 14 poles, and no louder than my first motor.

Looking at my gearing and Kv my current plan it to go up to 12 cells NiCd with some sub-C 2.4Ah cells. My system model says I'll be able to get 300 watts of power to the pedals at about 70rpm cadence, and about 4 minutes of run time.

The mount to the Linear's frame is all finished. I'll get pictures of that when the motor is in the drill case and ready to install on my bike.

Marty

[paultrafalgar]

Not wishing to dampen your enthusiasm, but I could have sworn that I read on here that Right Angle (worm/crown) gears are very inefficient?

[TylerDurden]

If the bike thing doesn't work out, there's always large animal dental work.

[lawsonuw]

Well I got the motor in the drill case and the whole mess re-installed. Switched back to driving into the slack side of the chain. I think it looks cleaner. The frame clamps and mount work great.

I've taken it for a ~10 mile shake down run. The 13T freewheel I've got is driving my nuts with its loud ass clicking. Anyone know how to shut it up? This new system pulls better than my last motor, but it's spinning a bit too slow. Maximum assist is at a cadence of 50-60rpm. When it's on this system is much quieter than the last motor. Gearbox still sounds like a coffee grinder, and it generates a subtle high pitch hissing noise. I can hardly hear the motor at all though. Oh yea, the new battery drains the battery quicker too.

I'll be making a couple of 1-2 cell booster batteries to hook inline with my current pack. I want to confirm the best battery voltage BEFORE I buy a new battery pack. I'll also be upgrading the 5ft 12-14awg battery wire to 10awg to reduce system resistance.

@Paultrafalgar: The gears in the drill are spiral bevel gears, and they are at least as efficient as straight tooth bevel gears. Specifically since the axis of the input shaft and output shafts intersect, the gears have an approximately rolling contact and waste very little energy.

@TylerDurden: ... Last time I checked dental drills spun a itty bitty bit faster than 219rpm. Though I have to say the blaze orange case of the drill adds a whole new level of ghetto to this bike

First picture is the whole system ready to install in the bike.

Second pic is a closeup of the system installed on the bike.

Edit: the converted drill weighs 3lb 10oz (1643grams) I estimate that the whole system weighs about 6lb.

[TylerDurden]

Heavier grease in the freewheel should help suppress the noise.

IIRC, Shimano FWs are fairly quiet.

[lawsonuw]

Well, 14.4v really livened up the performance of this assist motor. Unfortunately 14.4v was also too much for the second stage planet gears from the drill.

I just ran some numbers and it looks like I could use my current motor and planned 14.4v to friction drive the rear tire of my Linear with a similar assist force as the WE hub in my Trek produces. (though only weighting 3lb + battery instead of 15lb+ battery) I'd use a light spring for the initial force on the roller and use the roller's reaction forces to generate the bulk of the normal force on the roller. Preferably the roller would be pulled off the wheel automatically when the motor was off.

Bhaa! I think it's time I stopped messing around with the cheap stuff and just do this right. Just had a hint of a snow flurry, so this project goes on the back burner till my winter bike is up and running. (a Marin Alpine trial with a Cruzbike kit and studded tires, waiting on the kit now)

Marty

[Papa]

The 13T freewheel I've got is driving my nuts with its loud ass clicking. Anyone know how to shut it up?

It's the polygonal action in combination with the roller/sprocket impact during initial meshing that is responsible for most of the noise (assuming it's lubed, tensioned and aligned correctly). Basically, after one of the chain rollers engages and is seated, further sprocket rotation accelerates the following roller's engagement velocity, causing it to 'slap' the sprocket's roller saddle.The larger the sprocket diameter, the lower the chain engagement velocity (and the lower the noise). Given the pitch of the typical bicycle chain, cogs smaller than about 15 teeth should be avoided.

[lawsonuw]

The 13T freewheel I've got is driving my nuts with its loud ass clicking. Anyone know how to shut it up?

It's the polygonal action in combination with the roller/sprocket impact during initial meshing that is responsible for most of the noise (assuming it's lubed, tensioned and aligned correctly). Basically, after one of the chain rollers engages and is seated, further sprocket rotation accelerates the following roller's engagement velocity, causing it to 'slap' the sprocket's roller saddle.The larger the sprocket diameter, the lower the chain engagement velocity (and the lower the noise). Given the pitch of the typical bicycle chain, cogs smaller than about 15 teeth should be avoided.

um, no. The 13T freewheel shuts right up if the motor is running. (have to be pedaling) It is the ratchet paws hitting the 'gear' they engage making all the racket. Heavier grease, making the paw springs weaker, shortening the paw springs, or a different brand are the solutions I'm currently considering. As it is the freewheel clicks are nearly as loud as the gears/motor.

Slept on my gear problems a bit. The broken gear in the drill looks like it is brass. I could replace those with stainless steel or hardened steel and keep them from breaking again. I also think I need to add a second bearing to the output shaft. It's quite likely that only one of the three planets is taking all the load while the other two planets sit idle due to the output shaft shifting under power. An extra bearing should fix this.

Marty

[Papa]

Marty,
Even tho I lean towards synchronous belts, I think your creation is brilliant. Thank you for making it available in such vivid, reproducible detail. I'm reminded of John Tetz's addon: http://www.recumbents.com/wisil/tetz/e-assistmetric The trend towards tire smoking HP in bike conversions leaves me disinterested. Just seems counter intuitive to walk away from a HPV with clean, unscratched pedals - just mho. I have two, fresh 14.4 3ah Li-ion packs (w/matching charger), but am still fretting over motor and drive selection. Hard-headedly, I'm trying make the jump with only one reduction.

Re: chains and sprockets

After rereading your noise complaint, the word 'clicking' finally jump off the page, (ooops!) - ok, I screwed up. However, the noise dynamics of chains and cogs, imo, is worthy of mention for those who experience it, and don't know why - it is very real. After looking at your install again, the minimal chain wrap around the 13t cog would seem to explain why it doesn't appear to be an issue on your bike. Maybe a fiberglass cover would help curb the clicking - or perhaps move the motor assy aft, and under the seat?

[johnrobholmes]

Freewheels are noisy. That particular freewheel doesn't have anything to hide it from your ears, and it is pretty close as compared to a normal bike. A shroud would be a great idea, it would reflect or absorb the higher frequencies.

[TylerDurden]

FWIW...
http://www.endless-sphere.com/forums/vi ... f=2&t=4527

CCCpawls_Shimano.jpg (47.65 KiB) Viewed 1215 times

[lawsonuw]

Freewheels are noisy. That particular freewheel doesn't have anything to hide it from your ears, and it is pretty close as compared to a normal bike. A shroud would be a great idea, it would reflect or absorb the higher frequencies.

What's really annoying is that the 16T shimano freewheel I was using earlier was virtually silent. Good idea to add a shroud, It'll likely acquire a foam cover when it's used next. Tyler, after showing that picture I'm going to have to gut my 13T freewheel and take pictures

@Papa: I also looked at making the jump from motor to bicycle chain in one stage. Using the 13T freewheel does help a lot. Still If I want a 300 to 500 watt burst to get me up a hill and a decent system efficiency, It's looking like I need minimum 24v and 20:1 between the motor and freewheel. The only gearboxes I know of that can do 20:1 in a single stage while staying compact are worm gears (crappy efficency), harmonic gearboxes ($$$$), and hypercycloidal gearboxes. Commercial hypercycloidal gearboxes are expensive, but if I had easier access to a CNC mill I'd be tempted to make my own hypercycloidal gearbox just to see if I could.

I just did a quick calculation of how much power a system would need to boost me up any hill, 20% grade max, at a decent speed, like 10mph, it's about 1075watts! For that much power I'd rather drive the rear wheel directly with car alternator converted to a motor. Gear the alternator for 10mph peak with full field and add a throttle supervisor microcontroller to control the motor's field and armature current.

I also think I've figured out an elegant way to make a high efficiency friction drive. My current components have about as much power as I'd want to put through a friction roller so I'll likely hack this together next to play around.

Marty

[Papa]

Tyler,

Good stuff on the freewheels. I opened an ACS "South Paw" (ACS's LHD) a while back, and was greeted with 4 pawls and 18 groves. It also had a stack of shims for incremental bearing adjustment. Chromoly I believe. Still goes "tick... tick... tick", when spun so doubt it's any quieter.

[lawsonuw]

A few updates. I've done some further investigation of my crunchy gearbox and noisy freewheel.

First up a closeup of the gears I broke and abused. The 7 tooth sun gear has several large dents from chewing on broken teeth, and shows visible smearing of the tooth surface. I.e. the tooth pressures were large enough to reshape the sun gear... it won't last long. Also, the one planet I pulled clearly shows the particular sheen of a powder metal part. Powder metal parts are usually quite hard and wear resistant, not going to be able to make stronger gears for this tranny.

Closeup view of the gears that I was overloading.

Planetary from HF drill.JPG (248.37 KiB) Viewed 1084 times

Next up is a dissection of my freewheel. The cover has a left hand thread. This picture clearly shows the extra large springs with plenty of pre-load and no drop in force as the paw nears full engagement. *sigh* Shimano needs to make a 13T freewheel.

the extra strength springs that push full force all the way to the ratchet "gear" are what make this thing bloody noisy.

Noisy ass freewheel.JPG (130.4 KiB) Viewed 1001 times

Last up a prototype of little gem I found while investigating the Rolamite mechanism I'll be using in my friction drive.

Variation of a rolamite found in patent 3691871.JPG

(115.38 KiB) Downloaded 63 times

Basically its a simple way to get a LOT of belt wrap on a flat belt. When the large idler is loaded with a spring (or rubber band like the picture) the belt grabs strongly in one direction, but slips easily in the other direction. I'm thinking this would be a good match with the first motor I used. Using the 5mm shaft I could do 30:1 in one stage with "only" a 150mm diameter output pulley. Getting the belt to track strait will be a bit of an art, but careful alignment and crowned pulleys should do the job.

Marty

[EVTodd]

I know I say this every time I see a thread about friction drive, but... You can save a lot of trouble by not making a spring activated system to raise and lower the roller if you use a roller with a clutch bearing so it freewheels when not being driven by the motor. The cheap route is to buy an ev warrior roller with the bearing already in it. Here's a link:

http://cgi.ebay.com/2-EV-Warrior-Electr ... 286.c0.m14

I'm currently using one at 36 volts which on my bike with a friction drive Kollmorgen gets me 22 mph with pretty good hill climbing.

[lawsonuw]

First update: Winter commuting. My Marin/Cruzbike is a bust for now. I'll continue learning to ride it when the snow clears . In other news my Linear now has full studded tires! Had to mod my repairs to get room for the tire in the back, but everything fit nice. Have to run funny air pressures in the tires 20psi in the front, and 45psi in the back. I'm going to see how well 70psi works in the back next.

Now on to the picture below. It's a little toy I hacked together to test belt tracking. With the belt and crowned pulleys from SDP-SI the belt tracks true when the big pulley goes clockwise, and runs a bit off center in the other direction. Also looks like the belt has enough stretch that a fixed idler will be fine. If I add some flex in the right spots it should also be able to shrug off sand and grit.

Now the juicy bits. It's about a 15:1 (81.5/5.5 to be exact) reduction in one stage, and COMPLETELY silent. I could easily use this for the first stage reduction for a 40krpm plus motor. Current plan is to scale it up a bit and use my other motor and a ~20:1 belt to drive my linear. Not sure how long the belt will last, I am pushing it a beyond it's specifications but I'm staying well clear of it's breaking strength. I've got some other belt ideas up my sleeve if I shred this belt. Best of all, I can make my own pulleys for this!

Marty

[liveforphysics]

I Love this thread, it love this bike, and I want to know how your new pulley setup worked out!

[lawsonuw]

At the moment the pulley setup is on hold. I've got 2/3 of a design for it done. I need to fill in the last details and do a design review. But, "minor" things like getting a job or getting into graduate school are sucking up all my time.

I have done some upgrades to the base bike though. It's got a front fairing, this is primarily for rain/wind protection. The other thing keeping this on the back burner is that I'm getting into better shape! so doing my commute on leg power alone is less of an issue. I've attached a picture of my new fairing with poncho attached. i.e. ready for RAIN.

Lawson

[greygandalf]

Hi, I think your recumbent mod is brilliant!
If you see this post, maybe you could post an update? You were changing the setup to use a belt.
Were you intending to use a toothed belt or not? Interestingly, trek have made an urban bike with a belt drive (internal hub multi-gears).
I have a question about the motor you used (Turnegy - SK42-50-650) . It would seem that this motor is "intended" for use in model aircraft - as such it would get plenty of airflow to keep it cool. Did you find it got hot in use? Was being exposed to the elements ever a problem (for the motor that is!)? ie did it ever get wet ? I have an application, in a boat, where it may be enclosed (or get a bit wet!), so might have to consider some cooling. Thanks.