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Help with Picking a DC motor for Electric Handcart

  1. Sep 19, 2016 #1
    Hello,
    So I am in the process of designing a stair climbing electric handcart/dolley capable of lifting around 500 lbs {Washer/dryer or Refridgerator} up stairs. The idea was to use an electric motor, preferrably DC for HighTorque Low Speed and for my powering options. The idea was to use the 3-wheel stair climbing system already in existance, but to put a sprocket on a solid axle, and use a chain hooked to an electric motor to turn the 3-wheel system therefore, climbing stairs. Even better if I could use reverse on the motor to control descent as well. The class im in is Intro to Engineering Design, and no attention has been put toward any physics calcs so Everything I am learning for this project has been from google.

    If anyone could help Steer me in the right direction It would be a big help. I am fresh out of the Army so I have forgotten alot of the technical info from HS days, and being a Combat Engineer(SAPPER) doesn't help me with this. If the cart needed blown up, Icould do that no problem!! lol If anyone out there could provide me with good websites to help break down some of these torque calculations, and any tips about what else to include in my design calculations so hopefully my first shot at prototype is close to success, all would be greatly appreciated. If someone has a good idea for a type of electric motor worth using on this project, also would be a help. Im leaning toward a winch motor from an ATV hoping it can handle a 300-500lb capacity without burning it out. Once again, this is for a school project, my first engineering class which seems to emphasize more on AutoCAD rather than Physics. Thank you all in advance!
     
  2. jcsd
  3. Sep 19, 2016 #2

    berkeman

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    Welcome to the PF.

    Can you post some pictures of existing 3-wheeled stair climbing apparatus? Especially ones that can handle that amount of weight...

    BTW, since this is for a school project, the thread may get moved to our "Homework Help" schoolwork forums. We can offer hints and suggestions on your project, but we are not allowed to do the calculations for you.

    And thank you for your service! :smile:
     
  4. Sep 20, 2016 #3
    Absolutely understandable. I do not wish for the calcs to be done for me, because how could I learn them for future projects unless I do them. I only ask to be pointed or given the specific calculation/formula that I must figure out in order to get the desired answer or outcome I need.. Thank you for your help.

    This is the 3-wheeled stair climber cart that I have seen, but is probably rated for about 50 lbs max. My hopes is to completely beef up the basic idea with bearings, solid axles and machined aluminum/steel mounting brackets so that the wheels and axle can support the weight at standstill and also the torque of the chain/belt system pulling on it.

    I have a hard time understanding wjat size motor I will need to use in order to lug this weight up steps. My understanding is a DC motor is ptobably best option, and to add a Capacitor or maybe convert a small 12v rechargeable battery to the cart to power it without an ext. Cord. Odds are I would only need the motor/cart to run at full speed for under 15 minutes [time it takes to power up maybe 20-40 steps/maybe 2 flights or stories]
     
    Last edited by a moderator: Apr 18, 2017
  5. Sep 20, 2016 #4

    berkeman

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    Last edited by a moderator: Apr 18, 2017
  6. Sep 20, 2016 #5
    xxx4.gif original_357326_ThndTiu48DDqoPCQg6XYAGGvh.jpg
     
  7. Sep 20, 2016 #6

    berkeman

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    BTW, I would probably shoot more for the 300 lb end of this range. 500 lb loads are getting very dangerous to handle...
     
  8. Sep 20, 2016 #7
    On this setup, each of the 3 wheels rotate independantly of the others, which allows good mobility and turning radius. my plan was to use a straight solid axle with a sprocket or something, linkking the two sides together on one axle and then running a chain or belt to an electric motor. This wheel setup is rated for 400 @ the frames capacity, and each wheel is 320lb cap. for a total of 640 x 2?(2 of the three wheels would be contacting the surface at a time, third wheel would be in mid rotation, for a total of 4 wheels contacting the surface at any given tiime.
    With the actual wheels independant of the mounting bracket and the axle itself, this plan would still allow human power to move the cart and weight on flat surfaces without imput from the motor. Essentially, the motor is only there to rotate an axle, which rotates the mounting brackets for the wheels, alloowing it to climb stairs.
    Ineed the formulas that sould tell me how much torque the motor and axl will encounter under load (climbing stairs) and the formula that shows me what size motor to purchase for my teams project. Ive read that around 5 HP should be plenty sufficient, but no math to support that claim. I understand no calc will be done for me and that is fine. I just would like to know how to choose the right motor basid off of formulas that currently I do not know. Thank you for your help!!
     
  9. Sep 20, 2016 #8
    Berkeman, youre right!Just pulled avg weight of a Refridgerator and roughly between 200-250 lbs, so a highcap of 300lb will be plenty sufficient. Thanks!
    I figure the load will be more stable if tilted back to be closer to parallel with the slope of the stairs, rather than perpendicular to the ground (Straight up and down) I figure with the weight more balanced in the parallel fashion, would be easier for the cart to lift (More pushing than lifting) and easier for the human hand to balance the cart.
     
  10. Sep 20, 2016 #9

    berkeman

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    There are some important limitations on the simple 3-wheel design in terms of powering it to climb stairs. What happens when the rise and run of the stairs change? In the Google Images, the design that I found that is based on the 3-wheel design had an important other feature that made it much more practical for climbing variable size stairs...
    Yes, the load needs to be tilted way back while climbing stairs. You can see this on the videos of the better stair climbing hand-carts with loads like washers and refrigerators...
     
  11. Sep 20, 2016 #10
    do you have a link to the cart you were talking about? I was thinking instead of a triangle shaped mounting bracket, I was thinking more of a Peace Sign like a Mercedes symbol w/o the ring & With the wheels on theends, so the bracket wouldnt catch the edge of the stairs. The wheel design is still up in the air, but figured if there was already a stair climber, just improve it with a motor. There is the possibility of using something along the lines of a paddlewheel like a steamboat uses,but to climb stairs. I fear the resistance on the paddles would be too high and might break off.
     
  12. Sep 20, 2016 #11
    It seems that the wheels would need to be fixed and non-rotating, to do a powered handcart. Right? Freewheeling works great when the force is applied on the handle. So maybe the three wheel units become something like a three lobed, solid shape?
     
  13. Sep 20, 2016 #12

    berkeman

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    It's a couple pages down the Google Images search that I suggested. Look for a person using the device to lift a cloths washer up some stairs. The website has a very cool video... :smile:
     
  14. Sep 20, 2016 #13

    berkeman

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    This is good enough that I think it would be good to have it posted in this thread for future searches. Why is this such a good solution to the problem? Note the lift capacity...

     
  15. Sep 21, 2016 #14
    Well I have the design autocad ed out, now I just need help with understanding the calculations/formulas so I can figure out what motor will power my system/handcart. Perfect world would be a DC motor, with 2 output shafts, thats capable of lifting around 400lbs,[ my max weight cap is 250lb] do you think a winch motor would work if I stuck with a single shaft? For example, remove the spool and input a sprocket and chain instead? Winch motor capable of 800lb likr an atv winch or something of that nature?
     
  16. Sep 21, 2016 #15

    billy_joule

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    You first need to define the required specs; how fast you need to climb stairs.
    Climbing stairs increases the potential energy of the cart. E = mgh
    The rate of change of energy is power:
    P = E / t
    So required power is determined by the cart mass and change in vertical height per second.
    Once you decide on wheel diameter then you have output power and output rpm, you can work back and spec a motor.
     
  17. Sep 21, 2016 #16

    billy_joule

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    Note that you'll also need some failsafe mechanism to stop the cart free wheeling down the stairs - that could cause a fatal accident.
     
  18. Sep 21, 2016 #17

    RonL

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    I have not looked anything up, but you might find some interesting solutions looking at electric powered hydraulic systems, as in powered lift gates, they come in all sizes, lots of mechanical parts that might make a more powerful and compact system for a stair cart design.
     
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