vehicle power calculation

What do your numbers say? And why do you not believe them?

1 HP =746 watts, so 360/746=0.48 HP. Now 1 HP is the power required to raise 33,000 lbs (or 33000lbs/2.2lbs per kg = 15000kg) 1 foot in 1 minute. Let's see, 1/15000 x 0.48/kg = 7,200kg. In other words 360w can lift 7,200 kg to to a height of 1 foot in 1 minute without any special rigging for mechanical advantage, so neglecting friction and other mechanical energy loss, 360w is more than adequate for moving 160 kg. upwards against gravity. However, the speed at which the 160kg can be lifted is (7200/160)kg = 45 foot per minute or; (45ft/1min)x(60min/1hr)x(1mile/5280ft) = 0.5 mph. You should be able to eke out a little more speed in horizontal motion since our calculation is for vertical lifting against gravity and no friction in motion. For horizontal motion we cannot neglect friction, which would depend on the surface (paved etc.), the kind of wheels and other mechanical friction in bearings etc. Maybe about 0.7 mph maximum. My E-mail is: ecarlosingh@yahoo.com

I think you are being too pessimistic. The calculation for vertical lift does not relate very closely to horizontal motion, which will involve primarily acceleration, wheel/bearing friction, and air drag.

Studcentury-- This sounds like the equivalent of two healthy riders on a bicycle built for two. I'd say maybe 15km/hr with a smooth level road and plenty of pressure in the tires.

Really the speed on a level gradient depends entirely on friction losses (mostly in the tires), air resistance and the roughness of the surface. To manage acceleration and hills a robust bicycle chain drive and shifting system would work well and be fairly efficient. Other variable speed systems may be too inefficient. Energy to climb hills and accelerate will have to be subtracted from the total available to move the vehicle against friction and air drag.

Your best bet is to find a suitable large three wheel or 4 wheel cargo carrying bicycle and have someone with a pickup truck tow it at low speed while an observer watches the readings on a heavy (like 25 or 50 kg scale) attached to the tow line. To make this work you may need to contrive some way of dampening the scale readings so the pointer is steady enough to read. Once you know the drag force at low speeds you can multiply it times the velocity and that gives you a graph of power required for each speed.

A good number of gear selections will enable the vehicle to climb hills, accelerate at a reasonable rate and power against headwinds. Some close observation of your own experience riding a bicycle will be very helpful here.

Ed Weldon

Other posts have told you that you have about 1/2 a HP and that this is about the output of 2 moderately fit males....meaning that they could produce that output for maybe ten minutes or so. For sustained output you'd need more like 3 or 4 of these males!. While all this is interesting and would allow you to conduct some crude, albeit useful, exeriments, it's hardly a good engineering approach.

You'll need to get some better figures - chec the web (it's a while since I did this) but at low speed most resistance is "rolling" rather than "wind". In vehicle design these two terms start to be about equal at about 60 or 80 kph.

If rolling resistance is about 2% then a 160 kg vehicle will need about 160 x 9.8 x 0.02 Newton force (about 30N in this case) to maintain velocity. Any additional force will contribute to acceleration according to F = mass x acceleration, being careful to use N for force and Kg for mass of course! At higher speeds there will be more wind resistance and less acceleration.

Back to the rolling part. With 360 w of power and a rolling resistance of 30N the steady state velocity on the level (no air resistance) will be 12 m/sec.

Factor in what extra you need for acceleration (F=ma), air resistance (usually drag coefficient of about 0.4 x vel squared x cross-sectional area) what you need to allow for, drive train friction loss (say output = 0.8 input), any hill climbing power at cruise speed (at least another 2% slope or rolling resistance) and you will have something like the answer you need.

Thanks Ed, but for your information....I am a little bit older than a student, and by about 40 years. My experience includes some serious engineering, including the design of a full size airport fire engine, several vehicle standards and military equipment.

I am reminded of the time I had to accept or reject a fuel pump after a particular failure, a scientist suggesting two or three possibilities and indicating that it would take six months of research to resolve the matter. That was an un-affordable luxury - I had a day or so to decide on the cause, and did get it right. Point being that not all engineering is at the "space engineering" end of life.

My answer was couched in terms of a quick feasibility check and the sort of thing a student might want. Yup, if it was a full size project then a lot more homework would be needed, but then if it was a full size project, heaven help whoever if they need to come to this site for the sort design 101 question (that is also demanding the same time) that seemed to be asked.

Hey Trevor. 9.8 m/ second squared is standard acceleration for precipitating objects in a vacuum so you cannot accurately figure that in "F=ma" for horizontal motion.

Hi ecarlo. You may have misread Trevor's post. He correctly states: If rolling resistance is about 2% then a 160 kg vehicle will need about 160 x 9.8 x 0.02 Newton force (about 30N in this case) to maintain velocity. To calculate rolling resistance, you first need to know the force against the road, which is the mass times the acceleration of gravity. So a 160 kg vehicle exerts a force of about 1570 newtons against the road.

If we calculate the force required to overcome friction (rolling and aero) and to climb a grade, then any additional tractive force available can be used to accelerate the vehicle, according to F=MA. If, for example, we had 157 newtons available our acceleration would be (A=F/M) .98 m/s², (or 1/10 G).

Look at the power ratings for Zenn cars, or the available hub drive electric motors.

2000 watts should get you around town. 4000 if you want to go up hills with a friend.

The 1500# Zenn has a 5.7 kw motor, good for about 40mph with three people aboard. It's a real medium speed, full crash protected vehicle.

google "zenn specs"

thank you all for ur support...let me tell u briefly about my project it is a 3-wheeler prototype vehicle with 1 rear wheel and 2 front wheels and it is a rear wheel drive vehicle.the drive line would be simple FUEL CELL-SUPER CAPACITOR-DC MOTOR-WHEEL..the calculation i have done theoritically i got 168 watt needed to drive the vehicle at 30 kph neglecting all the frictional losses??if i have to achive 25-30kph average speed of vehicle with 360 watt motor is it possible if i include frictional losses??