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Me and my partner are trying to build electric pull carts to assist elderly Korean women and men who collect paper boxes for a living. These boxes are sold for recycling.

They work virtually at every corner of Seoul and it breaks our heart seeing them pulling those heavy carts up hilly roads in the city.

enter image description here

We wish to convert their manual carts to electric. We're no engineers so we need your advice on how to mod their carts to electric.

Below is a photo of how the wheels are attached to their carts.

enter image description here

I thought the best way is to purchase an electric motor hub (like this) and install it on one of the wheels and connect a new axle shaft below the body of the cart across to the other non-powered wheel. We use two brackets with radial bearings to connect the drive axle to the body - like these. The batteries shall seat flat in the cart evenly aligned in a row, keeping the cart balance.

My question is could the bearing and the bracket hold the weight of the body and load?

UPDATE: I'm getting many more replies here than the ebikes subreddit. You guys are a bunch of helpful people. Kudos to you!

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  • $\begingroup$ it isn't clear to me how you're doing it exactly, but a pillow block bearing holder will support any load that could be pushed around, but I must admist I've never seen one with a small bearing in it, they are used extensively in industrial applications. $\endgroup$
    – Tiger Guy
    May 27 at 14:32
  • $\begingroup$ Right @TigerGuy! I'm looking for pillow block. This one seems to have bearings with rotating shaft - engistudies.blogspot.com/2018/10/… $\endgroup$
    – ratib90486
    May 27 at 14:46
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    $\begingroup$ This sounds way too elaborate, expensive, and high maintenance to me and if it works then they have to drag around heavy batteries when it dies. Batteries are either very heavy or expensive and dangerously energetic requiring expensive chargers. One of those bateries is worth who knows how much cardboard and requires periodic replacement. What if you just go simpler and have one way clutch? $\endgroup$
    – DKNguyen
    May 27 at 17:48
  • $\begingroup$ What is done elsewhere in similar situations, are you reinventing the "wheel". In China in the 90's , small gasoline powered carts were very common . The operator would ride . The engines were 4 cycle , roughly 5hp. They traveled at low speed like 5 mph with the bicycle traffic. Not in Beijing but in smaller cities. I understand there have been many changes in China and it may now be different. At one time they filled a need. $\endgroup$ May 27 at 19:06
  • $\begingroup$ @DKNguyen There's a battery level indicator - green, yellow, red. When it turns red, it means it needs a charge. The user should be aware of this. I just learned about one-way clutch today. I don't see how it could fix the battery issue you mentioned. $\endgroup$
    – ratib90486
    May 27 at 23:16

2 Answers 2

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You will have a few problems.

  1. If only one wheel is driven the cart will turn as soon as the motor is energised. This may be unmanageable for the user and cause injury.
  2. The axle is fixed. It doesn't rotate. You can't transfer power to the other wheel. You would need a second motor and some fancy speed control to keep them in sync and to control speed for turning.
  3. Those hubs usually require wider forks on a bicycle so don't expect them to fit into an existing bracket.
  4. They're usually designed to run at up to 25 kph. The guy in your photo doesn't look like he could keep ahead of it and would be run over.
  5. The internal gearing will be optimised for the load of bike and rider. You may need a much lower gear ratio for a walking pace loaded cart.
  6. The hub motor usually has a freewheel so that the bike can be pedaled when the battery is flat. That means there is no reverse running so the cart can't be driven backwards.
  7. The cart has to be charged safely regardless of the weather and the user will need access to electrical power.

These are just a few of your problems. Each can be solved in some way but your challenge is to solve them all the the others that I haven't listed at the same time.

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  • $\begingroup$ It needs to be emphasized what a bad idea it is to power only one wheel. $\endgroup$
    – DKNguyen
    May 27 at 17:50
  • $\begingroup$ Thank you so much @Transistor for the insightful reply. The idea is to transfer the power to the other non-powered wheel via a new rotating shaft held by a pillow block bearing. So, if the powered wheel is energized the other wheel turns in sync. But I wonder if the cart will still turn as you said. I don't think having two motors are feasible because both have to be closely in sync, otherwise the cart will curve in the direction its heading. Freewheel and speed issues are noted. If you have any ideas on how to solve these, I'd be much obliged. $\endgroup$
    – ratib90486
    May 27 at 23:35
  • $\begingroup$ @DKNguyen If one wheel is powered while transferring the torque to the other wheel via a rotating shaft, would the cart still turn? $\endgroup$
    – ratib90486
    May 27 at 23:36
  • $\begingroup$ @ratib90486 No, it will not turn. This is why cars have a differential which allows the wheels to be driven but also turn at the different speeds. And if you give each wheel its own motor that is also problematic because now you need to give a way to control the speed of wheels for turning versus going straight. $\endgroup$
    – DKNguyen
    May 27 at 23:50
  • $\begingroup$ @DKNguyen Sorry, I'm no mech engineer so I don't quite get you. Do you mean in order to turn the cart, I need the two wheels to be traveling at different speeds. Ok, but the steering should be done by the user via the handle as seen here -> bit.ly/3t3L5cp $\endgroup$
    – ratib90486
    May 27 at 23:54
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You need an electronic throttle/ controller to start-stop and accelerate the cart like the one I have on my E-bike. I am sure you will find it on Ali Baba site at a reasonable price.

As regards the axel connecting the powered wheel to the slave wheel, you can use cheap centrifugal clutches used in go-carts that release the wheel under preset RPM. while the operator has throttled down. Then the operator can turn and power up.

Here is one sold for $19 on amazon.

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centrifugal cluch

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  • $\begingroup$ Yeah, we shall use a PAS sensor at the powered wheel and connects the power of the motor to a kill switch that is located at the handle. So, in order for the motor to turn on, the user has to squeeze the switch and pull the cart slightly. If the switch is not engaged, the motor will immediately turn off (for safety reasons). And thanks for the clutch thingy, didn't learn about this. Now I know. $\endgroup$
    – ratib90486
    May 27 at 23:39

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