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Servo Mechanism to initiate movement of an electric motor trolley

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namith11
#1
Jan10-14, 05:32 AM
P: 26
hey,

So I am working on this project where Im trying to come up with a motor set up to drive two wheels of a trolley. The entire trolley weighs 650 kgs and i require a motor with a torque of about 400Nm. I want to set it up in such a way that i want to be able to apply very little force to push the trolley after which the motor takes over n it moves forward by itself. When i apply a little force to pull it backwards the motor takes over n it moves in the backward direction. I don't know how to go about this. I will have to use some kind of servo assist mechanism but I am really not sure. Also steering will be completely manual. I need only forward and backward motion. Somebody please help me!
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SirAskalot
#2
Jan10-14, 03:55 PM
P: 136
Are you looking for advice on selecting a motor (drive system), or the control part of the system, i.e. the sensing of motion/force in a direction?
Okefenokee
#3
Jan10-14, 08:01 PM
P: 219
Is the problem that you are having difficulty getting the main motor to start moving the trolley from a dead stop?

namith11
#4
Jan10-14, 10:50 PM
P: 26
Servo Mechanism to initiate movement of an electric motor trolley

@Okefenokee: I want to know how i can get it moving in the forward direction with a slight push and in the backward direction with a slight pull.
@ SirAskalot: I initially wanted to go with a PMDC(Permanent Magnet) Motor that will run both wheels. I want to know if it possible to come up with a control system that will suit my requirement. Also do i need to replace the PMDC Motor with a Servo Motor? I have little knowledge about control systems and hence i have no idea where to start.
namith11
#5
Jan10-14, 10:51 PM
P: 26
@Okefenokee: I want to know how i can get it moving in the forward direction with a slight push and in the backward direction with a slight pull.
@ SirAskalot: I initially wanted to go with a PMDC(Permanent Magnet) Motor that will run both wheels. I want to know if it possible to come up with a control system that will suit my requirement. Also do i need to replace the PMDC Motor with a Servo Motor? I have little knowledge about control systems and hence i have no idea where to start.
namith11
#6
Jan10-14, 10:52 PM
P: 26
Here are the specifications of the motor if it helps :)
Power: 2HP
Torque: 400 Nm
Voltage: 12V/24V
Current: 120 A
Number of Drive Wheels: 2
Diameter of drive wheels: .435m
Type of motor: PMDC
Gear Reduction set up: Worm drive arrangement
Total weight being driven: 700kgs
Speed at motor: 1500rpm
Speed at wheels: 50rpm
Gear reduction ratio: 25:1
namith11
#7
Jan10-14, 10:52 PM
P: 26
Here are the specifications of the motor if it helps :)
Power: 2HP
Torque: 400 Nm
Voltage: 12V/24V
Current: 120 A
Number of Drive Wheels: 2
Diameter of drive wheels: .435m
Type of motor: PMDC
Gear Reduction set up: Worm drive arrangement
Total weight being driven: 700kgs
Speed at motor: 1500rpm
Speed at wheels: 50rpm
Gear reduction ratio: 25:1
SirAskalot
#8
Jan11-14, 11:32 AM
P: 136
Choice of motor also depends on your power source (i.e. battery, fuel cell, generator), load torque (you have said 400 Nm, based on what?), power ( what speed do you want?, air drag coefficient etc.) and speed/gear ratio.

A DC motor might be the simplest motor to control, so it would be a good place to start.

As for the control of speed and direction; you don't want a switch (i.e. a "gas pedal") to make it move? Or is it critical that it moves according to the pushing/pulling on the trolly? How can you make it stop?

Sensing a force (push/pull) might be easiest to do in the "handle bar" with the use of a switch. It could be done with the use of the motor or other sensors but its more difficult.

Sensing a motion in the trolly is easiest to do with a encoder or speed sensor.

With the input signal from one of the above choices some logic must be used to start/stop the drive unit. Simplest logic is a on/off switch between a battery and the motor. A more advanced choice is use of a micro controller or eqvivalent to initiate the starting and stopping.

Im not going to design the system for you. So you have to do some reading up on motor, drives and control to get it going. And might I advice to start at a smaller scale, with a smaller prototype. 700kg, 120 A are serious stuff!
namith11
#9
Jan12-14, 11:32 PM
P: 26
The set up will be powered by dry cell batteries. I calculated the torque using a motor sizing tool online based on my weight, average speed etc. I require an average speed of 1.2 m/s which is approx 50rpm based on my wheel dia. Speed at the motor is 1500rpm so i will be using a gear reduction set up to achieve this. Gear ratio will be 25:1
Also i do not require speed control and steering will be manual. So there will be this switch on the handle i have to press down and push/pull for direction and when i release the switch it will stop. There is enough friction in my motor to prevent it from rolling down a 15 degree slope when the motor is off so i don't need any kind of braking system.
I do not know much about the controls so i will read up on encoders and speed sensors. How hard is it to design a circuit for the same?
http://www.usa.canon.com/cusa/health...Specifications

Check out the above link. This set up is to run a Mobile Digital Radiography machine like the one the website mentioned above.


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