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Need to power man powered hand walking cargo cart

Hello - I have built a hand cart and we had a hub motor which failed / overheated wires / and overheated the controller ... tough thing is that we are need to haul 300-400 lbs up a 5-7% grade for approximately one mile - and needing to go to a max walking speed of 3 mph at full throttle - we are using 27.5 outside diameter fat tire bicycle wheel - plan would be to put a 350 / 450 / or 500 watt motor with a matching (or potentially a higher rated controller) with geared reduction 9 tooth motor sprocket and a very large (potentially an 80+ tooth) custom built wheel sprocket to get to an approximate 9-1 gear reduction - all that being said, what motor size / volt size / rpm size / battery size & amp hour battery size would you suggest for my needs ? Obviously needing very high torque with power to haul heavy loads and avoid overheating of any parts - FYI - I have attached a picture of our hand cart - thank you so much for the help , Jess

You have got everything figured out perfectly with the right size motor and top speed for the load and grade, etc. Here are some calculations that we ran for this project. 

The motor used for these calculations is item # MOT-24450SP which is a 24 Volt 450 Watt gear motor with 10 tooth sprocket for #420 chain. 

I know for certain that we can have a 90 tooth sprocket for #420 chain made with any mounting pattern that you need, whether it be for a freewheel or for bolting directly to the wheel hub without a freewheel. And if our machine shop's equipment is big enough then we will be able to have a 100 tooth or even 110 tooth sprocket custom made also. I will have to check on that to confirm though. A 110 tooth sprocket would bring the top speed down closer to 3 MPH than a 100 tooth or 90 tooth sprocket would, however, if we have to go with a 90 tooth sprocket then the top speed would be 4.1 MPH which is in the acceptable top speed range for the motor and gear ratio. The top speed can be controlled with a throttle to any level so if the top speed gearing is a little higher than 3 MPH top speed could be limited to 3 MPH by the throttle. 

As far as the battery pack goes a 24 Volt 22Ah lead acid battery pack is calculated to be the bare minimum size which is needed. I recommend going one size higher than 22Ah though, such as 26Ah or 35Ah so you do not run out of power, and also to allow the batteries to still provide enough power during the end of their lifecycle when their capacity starts diminishing. 

Do you want to have the wheel sprocket on a freewheel so you can push the cart forward by hand without any resistance from the motor? Or prefer that the wheel sprocket is solidly attached to the wheel so the motor will provide downhill braking?

Please let us know if you have any questions.

Thank you for the reply - much appreciated. When I used the calculator, I was using a 36 volt 350 watt, 9 tooth motor sprocket, 300 rpm, 81 tooth wheel sprocket, - this gave us a 9-1 gear ratio and approximately 3 Mph. Do you have this type of set up with the 9 tooth and rpm? And, do you have it in both 350 and 450 watt motors? And should I be going with a 36 volt - I noticed you calculated a 24 volt - shouldn’t I be going with a higher voltage pushing this much weight and to get more power? Very happy to hear you can build a big sprocket - very cool...thanks again for the help - let me know your thoughts - thanks again

We do not have any gear motors with a 300 RPM output shaft speed. The slowest gear motor we have in a 350 Watts or higher motor is 420 RPM. 

The motor's Watts rating alone will determine the power level of the motor regardless of its Voltage so it will not make a difference in motor power if 24 Volt or 36 Volt parts are used. However, if three batteries will fit into the cart better than two batteries will then that would make 36 Volts a better choice. 

With a 420 RPM motor the calculator is showing a 100 tooth wheel sprocket for a 3.1 MPH top speed.

Please let us know if you have any questions.

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