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Wheelchair

Please forgive us if this is a duplicate request.  We mistakenly created a request in customer service but don't know if we correctly created the original request in tech support.

Hello,

My science and engineering club at school is working on a motorized wheelchair project. The wheelchair will have four wheels. We have calculated torque for the two back wheels; it is 245 Nm. The back wheels will hold 70% of the mass, which is 87.5 kg (total mass is 125 kg - person and chair). We need to decide if we should use one motor for both wheels, or a single motor for each wheel. We are having trouble converting the torque to the wattage needed on the motor, and we also would like help identifying the rpm for the sprocket on the motor. 


We spoke briefly to support on the phone Friday and the recommendation was to use a single 24 V  450 W motor. We want to understand "why" that motor is the correct motor and try to apply it to the math we completed.  We would like to use your Tech Forum for this assistance. 


We have used your on-line gear ratio calculator and believe we will use a 26 inch wheel so a 2:1 gear ratio can be used to connect one of the back wheels to the suggested motor.


Would also like to discuss controller selection and possible battery selection as we continue to design our project.

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If you use one motor for powering both wheels and the wheels are connected together with a live axle then the wheelchair may have trouble turning corners because the wheels will not have any slip between them. If you use two motors and each motor independently powers the wheels then the wheelchair will be able to negotiate corners much better than if using a live axle.

I do not have any formulas or calculators to help convert torque to the Wattage needed for the motor. With 26" wheels using a gear motor with a 400RPM output and a 2:1 gear ratio the top speed would be around 15MPH. With a 125 Kg vehicle weight a single 450 Watt motor would be able to propel the vehicle on flat ground but would be a little underpowered going up hills and inclines. However with two 450 Watt motors the wheelchair would have ample hill climbing ability.

If you want the wheelchair to have a lower top speed then using a larger wheel sprocket would create a lower gear ratio and accomplish that. The RPM rating for the sprocket on the motor will be the same at the motors rated RPM.

After you decide how many motors to use and their Voltage and Wattage I can recommend a compatible speed controller. Regarding the battery pack; how may Volts do you want the wheelchair to be and what is your target mileage range on flat ground for the wheelchair?
We will meet Friday to discuss. We will get back with you soon. One question: we noted on your website that these motors are out of stock at this time. How long will it take to have the motors back in stock and available to order? The timeframe will need to be considered in our decision making process. Thanks!
We have a container of motors that just left Shanghai this week and are en route to us right now. They should take around three weeks in shipping however due to the dock workers slowdown it may take another three to four weeks to be processed after they arrive, and even longer if the dock workers go on strike. If the dock workers do not go on strike then we expect to have the motors back in stock in April.

We still have a good supply of 36 Volt gear motors in stock so if this is a project that you need to get started right away you may want to consider switching over to 36 Volt gear motors.

 

The team decided to use a single 24V 450W motor in the design.  We will not be able to use the suggested 36V motor for this project. For timing issues, we will not be able to wait for the delivery times you mention but feel we have found a motor to purchase on-line and will take this route for the motor.


We do wish to work with you and purchase the controller from you, plus any throttle control recommendations you have for items  that are currently in stock with your company.


Any additional recommendations, parts list, etc. are appreciated!  Thank you!


I can make a recommendation for the controller and throttle. I need to ask a few questions in order to make the best recommendation for your project.

Do you need the wheelchair to have reverse?
Do you want it to have a twist throttle or thumb throttle?
Do you want it to have a key switch?

 

Yes - reverse


Twist throttle (unless you can make a better case for thumb throttle)


Yes to key switch

The 24V 450W gear motors (MOT-24450G) are back in stock now. http://www.electricscooterparts.com/motors24volt.html

In my opinion twist throttles are easier to use than thumb throttles - thumb throttles always make my thumb sore after using them for a while.

For a 24V 450W motor with reverse capability here are the parts I recommend:

SPD-24500R (24 Volt speed controller with reverse) http://www.electricscooterparts.com/speedcontrollers24volt.html
THR-105K (twist throttle with 24 Volt battery gauge and key switch) http://www.electricscooterparts.com/throttles24volt.html

The size of the batteries depends on the range that you want the wheelchair to have. If you have a target mileage range then I can recommend a battery and battery charger size?

 

ESP Support - 


We received the parts order mid- March and worked to compile the electrical system for the project.  All the electrical system components worked well once we made modifications to the throttle connector. We are able to run the unmounted motor using the purchased electrical system. The project is progressing and the team is working to mount the motor and connect the motor to the sprocket on the axle. 


We have a question concerning how tight the bicycle chain we purchased from ESP should be between the motor and the axle sprocket.  We have tried looking for information on your site concerning chain tension. When we first tried to connect the motor to the sprocket, we continued to have the chain slip off. We actually think the tension is too tight but don't know for sure. The motor wants to pull towards the sprocket and we fear damaging the motor - this is why we think the tension is too tight..  We are working to re-enforce the motor mount but need to better understand the tension necessary for the bike chain.


Can you advise regarding the tension requiring on the chain when the motor and the wheel sprocket are connected? What is this for a typical motorized bike or trike?


A picture of the work in progress is included.  Thanks!


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You should have around 1/2" of chain slack in a properly tensioned chain. See figure "A" in drawing below to determine the chain slack measurement.

The chain should definitely have slack and should not be 100% slack-less or else too much pressure will be placed on the motor's bearings and they could wear out very quickly.


Having an overly tightened chain should not cause it to fall off though, in fact it should help to prevent it from falling off. Usually when a chain falls off it is from the sprockets being out of alignment, or from new and used sprockets and or chain being used together.


If all of the sprockets and the chain are new then it has to be an alignment problem. However If a used chain and or used rear sprocket are being used with a new motor sprocket that could be causing the chain to falling off. As sprockets and chains wear out during use the chain stretches and that causes the sprocket teeth to wear out along with it.


Here is an illustration that shows the most common sprocket alignment problems and what perfect sprocket alignment should look like.

I like to check sprocket alignment by eyeballing one of the sprockets against the other one like this.

Please let me know if you have any questions.

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