ebike towing force meter

[Doctorbass]

I am curious to measure the tow force of my ebike.
I bought a meter to measure the lbs or kg thrust force of my bike have with the 5305 at 84V

In theory, with a 50A controller at 74V (dropped) a 26inch wheel 100% throtthe i am supposed to get around 130Newton Meter at the wheel that is around 80lbs of towing force.

Easy to read large LCD display
Sleek hand held design
Display mode: kg/lb ( 50kg or 110lb)
auto shut off
Tare weight
Low battery indicator
Accuracy up to +/-0.05lb


I'll post resusts here when i'll get the gadget.

they are availlable from 5$ for max 88lbs on ebay http://cgi.ebay.com/Digital-Hanging...229512665QQcmdZViewItem?hash=item150229512665

 

[lazarus2405]

Careful there with your jargon. That 80lbs isn't "towing force". It's thrust, pounds force. A pound of force is the force exerted by one pound of mass by earth's gravity, or the force needed to accelerate a pound of mass at 32ft/s^2. When you say "towing force", it sounds like "towing capacity", the most mass you can safely control up hills, braking, and at whatever speed.

And "kg thrust" is incorrect, too. The SI unit of force is the Newton, while the kilogram is mass. When people measure "kg thrust", Isaac Newton cries.

Anyway, that meter measures lbs mass by measuring lbs force pulling on it - when hung vertically they're equal quantities; a 50lb mass suitcase exerts 50lbs force when hung from that hook. If you tied a line, though, to some stationary object like a telephone pole, the other end to your bike frame, with the meter in the middle, and gave it full throttle, you'd in theory get a max thrust reading. In reality, you'd either stall the motor or break the meter.

Though, you might get a momentary reading. When the clyte controller gives the wheel power but doesn't see any Hall sensor change, it kills power to keep from damaging itself or the motor. For a short moment you might get a reading, if the line was taught first.

A better method might be to get an accelerometer. If you can measure how fast you accelerate, and if you do it from zero, where you'll have maximum thrust, and you know the combined weight of your vehicle and rider, you can calculate your thrust.

Same with braking, but your braking force will include wind resistance, since you'll be at speed. You won't get your brake system's force, but that of your brakes plus wind.

Or, you could do wind resistance tests. Get up to top speed, start recording acceleration, and let off the throttle. The number you get as soon as you start decelerating can be used to calculate how much thrust you need to cut through the wind at that speed.

Wow.. now I want to get an accelerometer!

 

[TylerDurden]

That's a nice scale for 5 bucks!

 

[fechter]

I have one just like that. It does not have a peak hold feature. You must press the hold button to make it lock the display reading. Not bad for $5.

 

[Mathurin]

How about putting 1-4 popsicle sticks in the spokes and a playing card on the fork, then you record the sound with a laptop as you accelerate full throttle. Knowing wheel development, you'll have an accurate distance/time measurement this way. Knowing the total weight, you should be able to figure out a reasonable torque curve out of that, at least until you get to the point where wind makes it suck. Right?

 

[Link]

How about putting 1-4 popsicle sticks in the spokes and a playing card on the fork, then you record the sound with a laptop as you accelerate full throttle. Knowing wheel development, you'll have an accurate distance/time measurement this way. Knowing the total weight, you should be able to figure out a reasonable torque curve out of that, at least until you get to the point where wind makes it suck. Right?

LMAO! I did a similar thing to figure out how fast a motor was spinning. Plug a headphone into the audio in jack to the computer. Touch it to the side of a motor's driveshaft. Record it with something like Audacity. If you check the amount of time between the peaks on a waveform, you can calculate how many RPMs the motor is spinning at.

Then I bought an optical tachometer for like $30.

 

[lazarus2405]

How about putting 1-4 popsicle sticks in the spokes and a playing card on the fork, then you record the sound with a laptop as you accelerate full throttle. Knowing wheel development, you'll have an accurate distance/time measurement this way. Knowing the total weight, you should be able to figure out a reasonable torque curve out of that, at least until you get to the point where wind makes it suck. Right?

:lol: :lol: :lol:

I pray to God or anyone who'd listen that you're completely serious and not just poking fun at me. Because that make me sad if you were only being mean, be darn awesome if you were serious, and hilarious either way.

Edit after Link's post

Niiice use of technology.

Then I bought an optical tachometer for like $30.

 

[Mathurin]

Nah, I'm serious.

 

[D-Man]

A better way would be to find a tall tree/pole, get some weight lifting weights and some pulleys/ropes. Set it up so your ebike pulls the weights up into the tree. That way the bike keeps moving slowly rather then bogging it.

 

[Doctorbass]

A better way would be to find a tall tree/pole, get some weight lifting weights and some pulleys/ropes. Set it up so your ebike pulls the weights up into the tree. That way the bike keeps moving slowly rather then bogging it.

I plan to add a long spring to distribute the tension on few inches distance and avoid bogging it.

 

[fechter]

I plan to add a long spring to distribute the tension on few inches distance and avoid bogging it.

Yikes! be careful with that!
I'd hate to think of what happens if the spring breaks. Don't use an ACME spring.

How about putting 1-4 popsicle sticks in the spokes and a playing card on the fork, then you record the sound with a laptop as you accelerate full throttle. Knowing wheel development, you'll have an accurate distance/time measurement this way. Knowing the total weight, you should be able to figure out a reasonable torque curve out of that, at least until you get to the point where wind makes it suck. Right?

Actually, that would be a good way to measure the torque.
If you can accurately measure the acceleration, and you know the total vehicle weight (including rider), then the force can be easily calculated.
I've seen those little accelerometers they put in cars. One of those would be handy.
Something like this: http://www.piloracing.com/proddetail.php?prod=FX2

I think they make cheaper ones.
If you knew someone that had one, you could borrow it long enough for a test.

 

[Jozzer]

You DO know someone who has one doc, you wanna borrow it?

 

[lazarus2405]

Ooh now that's neat. Pricey, though. Perhaps we can convince Justin to add such statistics to CA, since it has direct access to the RPM and would not require an accelerometer.

 

[Link]

Hack one of these:

I know someone's done the same thing before on Hackaday 8).

 

[Doctorbass]

Careful there with your jargon. That 80lbs isn't "towing force". It's thrust, pounds force. A pound of force is the force exerted by one pound of mass by earth's gravity, or the force needed to accelerate a pound of mass at 32ft/s^2. When you say "towing force", it sounds like "towing capacity", the most mass you can safely control up hills, braking, and at whatever speed.

And "kg thrust" is incorrect, too. The SI unit of force is the Newton, while the kilogram is mass. When people measure "kg thrust", Isaac Newton cries.

Anyway, that meter measures lbs mass by measuring lbs force pulling on it - when hung vertically they're equal quantities; a 50lb mass suitcase exerts 50lbs force when hung from that hook. If you tied a line, though, to some stationary object like a telephone pole, the other end to your bike frame, with the meter in the middle, and gave it full throttle, you'd in theory get a max thrust reading. In reality, you'd either stall the motor or break the meter.

Though, you might get a momentary reading. When the clyte controller gives the wheel power but doesn't see any Hall sensor change, it kills power to keep from damaging itself or the motor. For a short moment you might get a reading, if the line was taught first.

A better method might be to get an accelerometer. If you can measure how fast you accelerate, and if you do it from zero, where you'll have maximum thrust, and you know the combined weight of your vehicle and rider, you can calculate your thrust.

Same with braking, but your braking force will include wind resistance, since you'll be at speed. You won't get your brake system's force, but that of your brakes plus wind.

Or, you could do wind resistance tests. Get up to top speed, start recording acceleration, and let off the throttle. The number you get as soon as you start decelerating can be used to calculate how much thrust you need to cut through the wind at that speed.

Wow.. now I want to get an accelerometer!

I did explain incorrectly, i appologize :wink:

Mass and weight are different.. one depend on the gravity and the other not.. i know that.. but i'm french and to explain physics by the book here to me is a bit more difficult then if i could explain it in french.. i have not the exact vocabulary guys :lol: a kg of weight on the earth represent a force f 10 newtons down on an object .. i understand that...
9.81m/s^2...etc...






SOME NEWS ABOUT THE METER!!! I received it today.

AND IT IS VERY STRONG!.. A METAL CASE..

it have an automatic hold fonction if the reading stay the same for 2 sec.. it read lbs, kg, oz and .. temperature!.. and it have a 39.5" tape measure!.. lol

Inspector Gadget need one!!

Doc