High torque velomobile

[jawnn]

This is for building a 5-600lb velomobile.
Or something like this cycle truck:

a one stage reduction


Basically I wan to drive 550lbs up the a 16% grade (max for 50ft) at about 5mph, that’s going to be about 200 rpm with a 2 to 1 gear reduction (16 sprockets on the motor 34 on the axle) on my 20” drive wheel.

So what do I do with 550lbs…16%…and 200 rpm?

I might be able to reduce the gear twice for a 400-rpm? But I am going to look for a gear motor, or at last an 1800-rpm motor.

 

[chuck]

Jawnn,

This is a simple problem. If it is broken down properly. I wrote a whole paper that covered all of this called physics, but I wrote it in the general discussion area and it was deleted.

Ok, We have the following
16% grade
5 mph
550 lbs

There are 3 forces that need to be overcome,
The force of gravity
The force of drag
The rolling resistance

Force of gravity is the slope x The weight
.16 x 550lbs = 88 lbs

The force of drag is 1/2 x frontal area x coefficient of drag x density of air x velocity^2
Physic students have been dropping things off of high buildings for hundreds of years, bicycle type objects generally have a coefficient of drag of about .9
The density of air is about .0728 lbs/cubic foot. Divide this by gravity which is about 32 feet/sec^2 gives us about .0023 slugs per cubic foot.
The velocity needs to be converted to feet per second. 88 feet/sec = 60 mph. soo... 5mph/60mph x 88ft/sec = 7.3 feet/sec
My frontal area is about 8 feet squared on my ride, close enough for this exercise.
Force of drag = 1/2 x 8 x .9 x .0023 x 7.3^2 = .44 lbs

Force of rolling, I think I measured coefficient of rolling at about .005 lbs, close enough for now, I will look through some old notes to see if I can find it. This did include my drive chain and motor, so it was pretty accurate.
The force of rolling is = the coefficient x (1- slope)(weight) = .005 x .86 x 550lbs = 2.4 lbs,, I think this is a little high, for some reason I think I have about a pound of rolling resistance.

We have 3 forces, add them up
Force of drag + force of rolling + force of gravity = .44 lbs + 2.4 lbs + 88 lbs = to about 91 lbs of force.

Power is Force x Velocity. Still with me?
The velocity we calculated above to be 7.3 feet/sec

Power is force x velocity is = 91 x 7.3 = about 665 foot pounds/sec

1 horsepower = 550 ftlbs/sec
665/550 = 1.2 hp required

We need to convert this to watts. 746 watts = 1 hp.
1.2 hp/1hp x 746watts = to about 900 watts at the wheel

chuck

 

[chuck]

jawnn,

Let me get this straight,
20 inch wheel
34 tooth wheel sprocket
16 tooth motor sprocket

Motors are in revolutions per min, so we need to calculate a wheel rpm, we must keep our units consistent.

A 20 inch wheel has a diameter of 20inches/12inches x1 foot of 1.67 feet
the wheels circumference is pi x 1.67 = 5.236 feet

Now the velocity of 7.3 feet/sec needs to be converted to feet/min

7.3ft/sec x 60sec/min = 438 feet/min

Find the rpm of the wheel divide the velocity of 438 ft/m by the circumference of the wheel which is 5.236 feet
the rpm of the wheel is 438/5.236 = 83.65 rpm

Find your motor rpm
Your reduction ratio is 34/16 .

the rpm of the motor is the wheel rpm x the reduction ratio = 83.65 x 34/16 = 177.76 motor rpm

If you ask, I will calculate the tension on the chain, this is chain breaking tension, just so you know. I would not build this with this reduction ratio , in other words, it is bad reduction design.

chuck

 

[swbluto]

My simulator. 'Nuff said.

 

[chuck]

Jawnn,

I just looked up in my Morse bearing and chain book, #40 chain at 100 rpm and a 16 tooth drive sprocket will handle .65 hp at 100 rpm and will handle 1.2 hp at 200 rpm.

chuck

 

[jawnn]

'Loquin' says that "this 665 foot pounds is more torque than a cummins diesel"...

Are you sure that this is right?

It's all beyond my brain power, but that does seem a bit high.

 

[rkosiorek]

it is not 665 ft/lbs of torque. torque is just force and distance. he is saying it is 665pound-feet per second. which is a unit of power or work done. that is a totally different animal than torque. one horsepower is equal to 550 pound-feet per second. which is the amount of energy expended to move a weight of 550lb 1 foot in 1 second. pound-feet per second is just a different method of expressing horsepower and not torque. 665pound feet per second is equal to 1.2Horsepower.

like chuck says it is just physics. and you are confusing the units of measure and what is being measured. which is easy to do if you miss or stop paying attention before you get to that very important "per second" part.

rick

 

[Chalo]

I just looked up in my Morse bearing and chain book, #40 chain at 100 rpm and a 16 tooth drive sprocket will handle .65 hp at 100 rpm and will handle 1.2 hp at 200 rpm.

Ordinary bicycle chains, even the thin 10- and 11-speed kinds, handle surges of several horsepower every day (usually with a bigger driving sprocket). Remember that pedaling force comes in shoves separated by dead spots, so the peak torque is much higher than the torque implied by its overall power.

 

[REdiculous]

Regular bike chain is pretty tough...I've got some old rusty chain on my trailer and it works just fine. I'll probably have to replace the freewheel before the chain now that I think about it.

 

[chuck]

REdiculous,

I just read your post on your build. Love it. I have never been the spit and polish kind of guy, like the mechanics, not the bling. Interesting. When I was a kid, I perused the neighborhood, scavenging parts, nailing and welding things together, used old motors and pulleys, made minibikes and go karts. All were fun, none lasted to long.

Unfortunately, I had to go to college and study. Parental pressure, I did not want to go. I am more of a hands on guy, would rather be in the shop than in the office. As a physics major I had to take a few injure-neering classes too. I have spent a lot of time the last 30 years since college working with power transmission design.

There are fundementals to good power transmission design that jawnn does not know yet. I know that jawnn is considering an etek type motor. That is a very powerful motor, hooked up to the correct batteries and the final gear ratio jawnn his considering would render bicycle chain useless in a very short time. I have got to run, I'll continue with good transmission design when I get back.

chuck

 

[chuck]

What is power transmission design?

I have used several primary reductions on my bike since the original version.

This one will handle 15 hp. 11/16th gates belt, 4" driven, 9" secondary, expected life, well over 20,000 hours






The primary drive on the bike now is the one on the right, this is also the most efficient drive pictured, gates 3vx belt, 3.15" primary, 8" secondary. Expected life at its rated power of about 4.46 hp is 20,000 hours. Since I run about 1.6 hp thru it, It should last in excess of 400,000 miles, conservative estimate.


I will re-edit this post, giving the actual efficiencies of each drive shown,

chuck

 

[jawnn]

Well I know this guy that builds these big trikes and claims that this is the only motor to use because he doesn't have to think about it. But then he says that the hub motors are even better....well I just keep thinking that I should use a leagal motor (that will require gears), even if the cops are not checking, and may not know what they are looking at.

He uses this on the tandom trike : http://thunderstruck-ev.com/etek_curve.htm
and a hub motor on the sinle person trike http://wildnaturesolutions.com/rockettrike.html

And my trike can't use a hub motor, so I must use some thing like a gear motor or make my own gears.
http://commutercycling.blogspot.com/2007/10/ez3-usx-trike-users-guide.html

SO HOW DO I FIND A MOTOR THAT WILL WORK? a motor that will produce 1.2hp at around 95rpm? (and still be able to move faster on less steep hills) But is there a manufacturer that has charts for their motors?

I get vertualy no time on the internet, so I have to take this home to read it and come back in a few days bewildered as usual.

 

[amberwolf]

And my trike can't use a hub motor, so I must use some thing like a gear motor or make my own gears.
http://commutercycling.blogspot.com/2007/10/ez3-usx-trike-users-guide.html

If that is your trike, I see no obvious reason it couldn't use a hub motor, at least in front.

SO HOW DO I FIND A MOTOR THAT WILL WORK? a motor that will produce 1.2hp at around 95rpm? (and still be able to move faster on less steep hills)

I use a brushed powerchair motor on CrazyBike2 to drive my regular bike drivetrain. It is nominally a 650w-ish motor (a bit under 1HP), at 24V. Running it at 36V, with the load I have on it, takes 15A-ish if I'm pedalling and cruising slowish, around 550W constant, or roughly half of what you need. It takes a lot more, in the 1.5 HP range with a heavy cargo load and faster speeds, or less pedalling; gets hot doing that. I'm sure with forced-air cooling, I could run it at more than 1.3HP for extended periods, perhaps constantly.

The nice thing is that at 24V it's meant to output about 120RPM from it's gearbox, and so even at 36V it doesn't take much reduction to get that to max of 90-ish at my drivetrain input to match pedalling speeds.

 

[chuck]

Jawnn,

I am a little confused too.

Read this again.
http://endless-sphere.com/forums/viewtopic.php?f=2&t=13418&start=0

What I need to know in order to answer your questions.

What is this trike to be used for?
What is the desired top speed of the trike?
What is the total distance you require this trike to travel?
What is the net change in elevation?
Do you have a picture of the trike you are interested in converting?

If you can answer the above questions I won't be confused anymore and I will be able to properly answer your questions
Is there a simple torque formula? No there is not. Is the mathematics difficult. No, I have made the calculations here using the math one should know by the 8th grade.

The concepts of Force, Energy and Power can be more difficult to understand. One needs to understand these three before the concept of torque.

Torque is a radial measure of force. It requires in its calculations the concept of pi and a high school level of mathematics of trigonometry to apply. Torque can be a monster, it is properly handled using college mathematics called calculas. In a static state torque is applied using algebra. Your trike is in motion which requires calculas to determine torque values.

Jawnn, answer the 5 questions from above with as much information as possible. Then we can proceed with answering your questions.

Respectfully,

chuck

 

[jawnn]

What is this trike to be used for? running around town with too much weight on the rear wheels, up steep hills that are wet most of the time.
What is the desired top speed of the trike? maybe 5mph on the hills.... or more...under 20 on the flats.

What is the total distance you require this trike to travel? maybe 30 miles.

What is the net change in elevation? the tallest hill, with a small amount of 16% is maybe about 200 ft

Do you have a picture of the trike you are interested in converting? its the same trike....there is vertualy no room except behind the seat for a motor. and it will be tight. the hub motor thing will not work...... so many people think it will and if I lived on flat land it could.

all I realy need is a big motor and a ratchiting free wheel for the axle that is I think 7/8th inch with a .5" key ... I may have to make one with a timeing belt sheave.

 

[jawnn]

this is what I call simple:

In laymen terms HP = Torque over a given amount of time. So... the formula is HP= (Torque X RPM / 5252) and the other way to convert it is Torque = (HP/RPM x5252) for this reason Torque is always higher than HP below 5252 rpm and they meat on a graph at 5252 rpm and HP is always higher above 5252 rpm.


So one other formula is there is 746 watts in 1 HP so 1000 watts is 1.34HP If you have a 1000 watt bike you have 1.34 hp and at 60 rpm 1.34/60x552 = 117 ft/lb torque this is a number based on 100% efficiency (not considering losses) and with out current limiting in consideration (most controllers will limit current or amps at low rpm)

 

[chuck]

OK Jawnn,

I am still not sure what trike you are planning to use. I went to your blog, saw more than one trike.

I asked the question wrong when I said net change in elevation, what I need to know is the elevation at the start of the trip and the elevation at the end of the trip.

To use torque in your calculations is going to be difficult to apply.

To build a trike to go 30 miles a trip at 20 miles an hour.

The hill is hardly worth mentioning. With the etek type motor you have chosen you will be able to fly right up that hill at 20 mph. The limiting factor is not the etek type motor, it is the ability of the batteries to supply the power up hill.

You will not need a transmission to go up that hill if the batteries can supply the power required.

Your speed will be controlled by your controller. I am recommending an alltrax controller, they are cheap on ebay. I use a npx 4830 non programmable controller, paid about $170 for it new from cloud electric on sale. http://www.cloudelectric.com/

My bike weighs about 200 lbs, me about 220 lbs
I use Sears Diehard Platinum deep cycle batteries, made by Odyssey, 24 volt system
A 1.6 hp scott motor
I will take pictures of some of the hills I drive up everyday that I think dwarf the hill you are describing at 30 mph
I do not have a ratcheting device or freewheel anywhere in my drivetrain
I ride upright with a large frontal area
Several of the hills have stop signs halfway up. From a dead stop I am up to 30 mph in just a few moments on the steepest 20% grade sections.
I have well over 10,000 miles on this bike now, upgraded to the 1.6 motor about a year ago, I was using a 1 hp scott motor before on the same sections for 3 years with no problems whatsoever.
My biggest expenses have been chargers. I now use diehard platinum chargers from Sears and they are the only chargers that have lasted
Tires are my second expense, at the weight I am at rear tires last about 2000 miles, Maxxis Hookworms at about 40 psi

chuck

 

[chuck]

First we need to estimate the energy requirements to size the battery pack

This is very straight forward, I will estimate your total rolling resistance at 5 lbs using a direct drive system.
the distance is 30 miles or 30 miles x 5280 feet/mile = 158,000 feet
the energy required to overcome rolling resistance including the drivetrain is 158,000 feet x 5lbs rolling resistance = 792,000 ftlbs of energy; this is not torque

Your frontal area on your trike is, hell I don't know, lets call it 4 square feet, 20 mph is 20/60 x 88 = 29.3 ft/s^2
the force of drag is .5 x .00273 x .9 x 4 x 29.3^2 = 4.2 lbs
the energy required to overcome drag is 4.2 lbs x 158,000 feet = 668,059 ftlbs of energy

the energy required due to the net change in elevation is 200 feet x 550 lbs = 110,000 ftlbs of energy

Total energy required is 792,000 + 668,059 + 110,000 = 1,570,000 ftlbs of energy.

I convert 70 percent of my battery energy to mechanical energy at the pavement, 1,570,000 ftlbs / .7 = 2,243,000 ftlbs of enery required.

to convert to joules, 3,041,099 joules, from an online calculator

845 watt hour battery from an online calculator

You will want some reserve in your battery pack, how much, I don't know, how bout 30%.

845/.7 = 1200 watt hour battery.

48 volts? 1200/ 48 = a 25 amp hour battery pack.

chuck

 

[chuck]

Now what about the maximum current,

http://www.cloudelectric.com/product_p/mo-et-2.htm

the motor you chose can draw 300 amps for 30 seconds,
Probably about 50% efficient from a dead stop until you reach 20 mph
that is about 10 hp,

150 amps usable x 48 volts = 7200 watts

7200 watts/746 watts = 9.65 hp

Says it will put out 8 hp continous at 150 amps, 8/9.65 = 82 to 83 percent efficient.

I read a lot of things here that say motors are 95% efficient, look at this

well, let me find it first, thought i had bookmarked it

chuck

 

[jawnn]

taking a wild guess...what do you think?
http://simongu.en.hisupplier.com/product-289680-900W-Electric-Lawn-Mower-Motor.html

I am also thinking of a gear reduction box made for internal combutstion engines...18 to 1 I think.

 

[jawnn]

I am still not sure what trike you are planning to use. I went to your blog, saw more than one trike. try this page all the same trike
http://funnyfarmart.com/ez.htm
I asked the question wrong when I said net change in elevation, what I need to know is the elevation at the start of the trip and the elevation at the end of the trip. no idea...its higher where i live but there is a lot of ups and downs.

To build a trike to go 30 miles a trip at 20 miles an hour. 15 on the flats is ok by me

it is looking like the only thing for me to do is use the big etek and big batterys in the trailer.....I have been trying to figure this out this for about a year and ahalf....and my knee is about gone,for pedaling, as of today.

 

[chuck]

Motor efficiency

http://newenergyandfuel.com/http:/newenergyandfuel/com/2009/04/06/japanese-researchers-breakthrough-96-electric-motor-efficiency/

I had a better article, this covers the same thing, just not as in depth.

Anyway, Jawnn,

There is nothing wrong with using to large a motor, generally oversizing an electric motor gives one a little better effiency, not to mention, in your case, depending on the batteries you chose, one very powerful trike.

 

[jawnn]

IS THERE ANY REASON THAT i SHOULD NOT USE THE BIGGER MOTOR? like would it use much more power?

 

[chuck]

Jawn,

I would stay away from exotic motors, brushed dc of the type you are considering, etek, mars, are good, very long lived motors. Brushed motor controllers from Alltrax are cheap enough, and, bulletproof.

From a gearing perspective you are better off using 20 mph than 15 mph, just use the controller to limit your speed. ie, stay out of the throttle.

I hear of a lot of problems with kelley controllers which are a little cheaper than alltrax. For ebike use the forum here says they are fantastic. My experiance with a brushed kelley controller was it did not work and I returned it to cloud electric for a refund. The nteea group here in Dallas has had a lot of problems with brushed kelley controllers in car conversions, our group is just chock full of electrical engineers. Richardson Texas is home to many very large electronic manufactors, Texas instruments, Motorala has a plant here, Rockwell bought Collins Radio,,there are so many I can't list them all.

Gearing. I am using pulley generically, it could mean sheave or sprocket....

To use a gear box you will need to buy a pulley for the motor, a pulley for the input of the gear box, a pulley for the outbox of the gearbox, and a pulley for the bikes axle. You don't have much room for a gear box.

Buy the same number of pulley's and use a jackshaft rather than a gearbox.

Run that Etek motor at 24 volts rather than 48 volts, that is a 50% reduction in motor speed, and you still have plenty of power (more than plenty) and lesson the reduction requirements.

I am looking at the chart at cloud electric for a mars motor, similar to what you are considering,
http://www.cloudelectric.com/v/vspfiles/assets/images/me0708data.pdf

It looks like about 1600 rpm at the motor is where the mars should be at for 24 volts. a good start.
At 20 mph your wheel rpm is 336 rpm.
1600/336 = 4.76 reduction ratio.

Tractor supply has pulleys for b belts that cost about 30 dollars for a 10 inch pulley, lets see if we can eliminate a jackshaft.
10/4.76 = motor pulley diameter = 2.1" this is too small for a drive pulley on a b belt.

http://www.tractorsupply.com/agriculture-farming-ranching/hubs-sprockets-chains/hubs/weasler-pulley-1-5-8-in-id-x-12-in-od-fits-a-or-b-groove-v-belts-4300143

OK, Tractor Supply has a 12" pulley, 12/4.76 = 2.52 .... better, not ideal, eliminates the jackshaft and gear box, and cheeeap. I like that. sku 4300143.

Let me see what gates says about this for a v belt.

There is no listing in my book for a 2.5" pulley. But, BX belt on a 3" pulley at 1600 rpm will handle 3 1/2 hp. A BX belt is a notched belt available at a bearing supplier for about $15 dollars.
Unfortunately, a 2.5 inch B sheave is too small for a B belt to be highly efficient. Life will also suffer. If you don't abuse the drive, this will handle 1.2 hp, it will be a fairly compact drive, and it is cheap. should last for a few years.

Otherwise, a jackshaft will be required,
Ya know, a complete drive for about a hundred bucks, not bad. It will be fairly efficient, for sure better than 85%. Probably about 90% not bad.

It will be more efficient than a gearbox, properly designed drives generally lose about 5% per stage reduction. Using a gearbox would mean at best an 85% efficiency because it has 3 steps of reduction.

Jawnn, Can a 12" pulley be mounted to the wheel or to the axle? Is there a place to mount the motor to line up to the axle pulley?

 

[chuck]

Jawn,

Using too large of a motor will not hurt efficiency. It is actually more efficient.

Lowering the voltage from 48 to 24 volts will not hurt the efficiency either. 4 gauge wire is the minumum size. I use 2 gauge. I once used 4 gauge and can tell the difference. I first used 6 gauge, which was recommended by kta services, where I bought my first motor and controller, big difference in performance on hills between 2 gauge and 6 gauge.

It can be hard to determine the actual reduction required. First I don't have the specs. on the ebay motor you are considering. This motor being a knockoff, may have smaller or less powerful magnets than the etek motors. This means the motor will run at a higher rpm than the etek it is being compared to. The armature winding count may be different. Too light of a load on the motor will cause the motor to spin faster, this can drastically reduce effiency. I once geared my bike at 10 to 1 instead of 9.1 to 1. My speed was the same, but, my distance plummeted, and my motor got very hot. It took me awhile to figure out what was happening.

Now back to the drive I designed. The Morse part number for the 2.5" datum diameter sheave for the motor is 2bk27. Any bearing supplier can cross reference this. The etek style motors generally use a 7/8" bore. There is also available a 2.6" datum diameter available. just in case this is over geared.

Further considerations. The motor must be mounted as far as possible from the axle pulley. I would say 12 inch centers would be the minimum distance between the motor and the axle. More is better. 13 inches would better than 12 inches. This is very important because of the extreme difference in size of the two pulleys. The center distance affects the arc of contact of the belt to the motor sprocket. The etek style motors have a lot of power and this drive is under designed.

Get a coffee can or something and experiment with motor placement to get an idea of how to mount the motor to get the maximum center distance possible.

Use a cast iron motor pulley or, better yet, a forged steel motor pulley. Do not skimp here. Buy this from a bearing supplier. The best motor pulley available, period. A tractor supply steel motor pulley will not be acceptable. Die cast zinc and aluminum motor pulleys will fail promptly. This will be the most expensive part of the drive.

The belt must be a BX belt. Not a BL belt, or any other type of B belt. Use only Gates, Browning, Goodyear or,,,, Dayton. Buy this belt only from your bearing supplier. Not from home depot, the auto parts store or tractor supply.

That is all I can think of for now.
Luck
chuck