the walker project

[thewalker]

greetings people!

My group from the philippines is working on a wheeled walker for elderly people. it shall be a walking aid. We have trimmed down our wheeled walker to 100lbs. its velocity will range from 1-4km/hr. it's wheel diameter is 11 inches. it is differentially driven. it will operate for two hours. This is the link of the motor that we are considering http://www.robotmarketplace.com/prod...-218-2001.html (http://www.robotmarketplace.com/products/AME-218-2001.html). please advise us if this is the motor that we need.

or do we need to use a permanent magnet motor? the problem is that can i step down its rpm from around the 2000 to 100rpm?

thank you, have a great day!

[AtomicZombie]

That motor you linked to is a Cadillac windshield wiper motor. Although it may have enough torque (one per wheel) to do what you want, the quality and efficiency will be rock bottom.

Windshield wiper motors have brass bushing on the main shaft, plastic gears, and very low overall efficiency.

Is this unit of your steered by controlling the speed of two motors or by gear differential?

Brad

[thewalker]

thanks for the info. i was really considering that motor.

it will be controlled by the speed of the two motors. what do you think is the most suitable? a permanent magnet dc motor? can i step down its rpm to around 100 rpm?

thanks brad

That motor you linked to is a Cadillac windshield wiper motor. Although it may have enough torque (one per wheel) to do what you want, the quality and efficiency will be rock bottom.

Windshield wiper motors have brass bushing on the main shaft, plastic gears, and very low overall efficiency.

Is this unit of your steered by controlling the speed of two motors or by gear differential?

Brad

[AtomicZombie]

Tell me the max weight you want the motors+batteries+controller to be and I will suggest something.

Brad

[thewalker]

hello,

around 30 pounds. forty pounds maximum. i plan to use an h-bridge controller for the motor, is this suitable? I plan to directly put the motor to the wheels. please advise

thanks brad :)


Tell me the max weight you want the motors+batteries+controller to be and I will suggest something.

Brad

[AtomicZombie]

What you are looking for may be tough to find. At that weight, most of the motors are going to be light duty and low quality. If it's only for a basic prototype then those surplus "Barbie jeep" motos might run it for a week or so.

Here is a motor in your range that is much like a windshield wiper motor, but better qualitiy and center timed + reversible...

http://www.npcrobotics.com/products/viewprod.asp?prod=40&cat=20&mode=gfx

On the much higher quality side, power chair motors will run ultra quiet and with great efficiency...

http://www.npcrobotics.com/products/viewprod.asp?prod=42&cat=20&mode=gfx

Also easy to mount your wheels, and will live at 12-36 volts, producing more than enough torque. Expensive, though.

Here is a perfect motor controller for those motors...

http://www.diverseelectronicservices.com/html/mc7_motor_controller.html

Good luck!

Brad

[thewalker]

What you are looking for may be tough to find. At that weight, most of the motors are going to be light duty and low quality. If it's only for a basic prototype then those surplus "Barbie jeep" motos might run it for a week or so.

Here is a motor in your range that is much like a windshield wiper motor, but better qualitiy and center timed + reversible...

http://www.npcrobotics.com/products/viewprod.asp?prod=40&cat=20&mode=gfx

On the much higher quality side, power chair motors will run ultra quiet and with great efficiency...

http://www.npcrobotics.com/products/viewprod.asp?prod=42&cat=20&mode=gfx

Also easy to mount your wheels, and will live at 12-36 volts, producing more than enough torque. Expensive, though.

Here is a perfect motor controller for those motors...

http://www.diverseelectronicservices.com/html/mc7_motor_controller.html

Good luck!

Brad
thanks a lot brad. the motor that u suggested is pretty expensive. do think a permanent magnet dc motor will do? is there a gearbox included? to step down the rpm.

thanks!

[thewalker]

we can push the weight to around 50 pounds. we need a robust and durable motor. is a 12v NiCd battery suitable for the dc permanent magnet motor?

[AtomicZombie]

It is a gear motor stepped down to 230 RPM. At 12 volts, it would probably be fast enough for a walker.

Yep, anything to do with mobility is always quiet, durable and quality made. Imagine what would happen if the unit failed 3 blocks from home!

Brad

[thewalker]

oh.. thanks man. can the pic24 control the motor controller that you suggested? it's gonna be one motor controller for each motor right?

[AtomicZombie]

Yes, the controller is perfect for wheelchair motors - I have 2 of them myself. You will need two controllers for two motors.

Another option?....

If the walker is steered by turning it, why not just wire the motors in series with each other? This way the torque across both will be constant as a sum of their total power. You could turn the walker, and the motor on the inside of the turning circle will slow down, causing the outer motor to speed up. It's almost like a free automatic differential. Now you only need one controller.

Brad

[thewalker]

brad do u know of a store in asia that sells the kind of motor that u suggested? please advise what motor. turns out the shipping costs for the motor is really expensive so my group is looking at the alternatives. thanks man

[AtomicZombie]

That's a little out of my district! If this is just a one-off project, try to find a used wheelchair for parts. Often something silly breaks on them and they go cheap.

Brad

[thewalker]

thanks a lot brad!

i checked this motor. here is the link:http://philippines.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0715106

is this comparable to the motor that u suggested from npc robotics? thanks man

[AtomicZombie]

No, that motor will not work for you. It is only 16 watts, and you will want one between 150 and 250 watts. That motor also has no gearbox, so it will run at 2000-3000 RPM, and you will want a final shaft RPM of between 50-100 RPM depending on your wheels.

Brad

[thewalker]

We encountered a problem with battery, motor controller and motor.

When we use a dc power supply, it turns on the motor controller and the motor runs based on our program. ALTHOUGH when we use the 12v battery it only turns on the motor controller but the motor does not move.

When we plug the battery to the motor without the motor controller, the motor moves.

Our program works. we have tested it with the motor, motor controller and dc supply

This is the link to the motor controller : http://parallax.com/Store/Microcontrollers/BASICStampModules/tabid/134/txtSearch/motor/List/1/ProductID/64/Default.aspx?SortField=ProductName%2cProductName

This is the link to the motor :http://parallax.com/Store/Microcontrollers/BASICStampModules/tabid/134/txtSearch/motor/List/1/catpageindex/2/ProductID/507/Default.aspx?SortField=ProductName%2cProductName

Please help us with our problem.

Thank you!

[AtomicZombie]

This would be your best bet...

http://forums.parallax.com/forums/default.aspx?f=7

Brad

[thewalker]

hello!

My battery's specs are 12V 7.2Ah/20 Hr. It's brand is FirstPower

what does this mean?

How much current can it supply for 1 hr? 2 hrs? 3 hrs?

Thank you!

[AtomicZombie]

You are asking questions about a custom design that I would have no chance of answering.

In basic terms, your battery pack "might" be able to spit out 7 amps for an hour. Of course, this is like asking how far can 1 go on 1 gallon of gas.

It really depends on the vehicle size, engine, efficiency, speed, load, friction, controller type, etc.

I think the ball is in your court now.

Good luck on your project.

Brad