# Electric Book Cart



## PStechPaul (May 1, 2012)

Well, first off, this depends on whether you just need to build or buy something that will do the job, or if you want to do this as a learning experience. There probably are some small motorized fork lifts or hand carts that could be used or slightly modified to do what you want, or you could have someone design it for you, for which it would be expected for you to pay for engineering, prototypes, and drawings and other documentation.

Assuming you want to do this yourself as an educational project, you may have a long road ahead if you are starting with not knowing anything about mechanics, motor, power, etc. I started as a child building projects using erector sets, tinker toys, and raw materials and parts I scrounged from junk. My father was an electronics engineer and machinist and I saw him build and fix all sorts of things, so I acquired some of his "knack" and gained experience on my own through trial and error, as well as formal education in high school level mathematics and physics.

Just as a starting point, I'll use my EVcalculator to come up with some numbers for you. Let's say the cart and rider are 200 kg or 440 pounds. And the top speed will be 5 km/hour or 3.1 MPH. The slope of your ramp is probably no more than 5%, which corresponds to an acceleration of 5% of the gravitational constant of 9.7. My calculator comes up with 31 pounds of thrust (the force you need to push the cart uphill), and at the maximum speed this is about 200 watts or about 1/4 HP. Now let's say you have wheels that are 6" diameter, or 150 mm. They will turn at 177 RPM with a torque of 7.7 lb-ft. An electric motor may have a nominal top speed of 3600 RPM which is about a 20:1 ratio. So you could use a wheel sprocket with 200 teeth and a motor sprocket of 10 teeth. Or you might need a double reduction drive with a 4:1 and 5:1 ratio. 

A reduction drive results in some loss of efficiency, and there will be other losses as well, so you will want to build this with perhaps twice the calculated values, or you may have to settle for less performance. But also remember that electric motors are rated at continuous duty, and for your cart you might only need to run it for less than a minute to get to the next level, and then it might have 4 minutes to cool down. This is a 20% duty cycle, so a 1/4 HP motor can easily produce twice the power for such short periods of time.

You can also determine the battery requirements from the data we just calculated. It shows about 62 Wh/mile, and you will probably be going no more than that in a day, so a 12V battery rated 5 A-h should do the job. If you use lead-acid (SLA) you probably want twice that, and there are many SLAs rated at 12 Ah which weigh only about 8 pounds and cost less than $30. 

I would suggest that you get some basic electricity kits and some robotics kits and build something to get experience. Once you feel comfortable with the concepts needed to build something like an R/C car then you can scale up to a project such as yours. 

HTH. Good luck!


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## PStechPaul (May 1, 2012)

[bump] Your thread might be better in the non-road vehicle subforum. 

Here are some existing products similar to what you propose, or as ideas:

http://www.liftproducts.com/electriccarts.html

http://www.electricwheelbarrows.com/

http://www.phswest.com/motorized_carts.htm?gclid=CN3t6ciz8rsCFRBnOgod-CoAXw

http://www.ebay.com/itm/EV-Electric...483?pt=LH_DefaultDomain_0&hash=item4618a0841b


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