In my project, I am using four 20kg torque DC motors, one 15kg stepper motor, two servo motors, 6 ultrasonic sensor, one bluetooth module and a arduino board.
What could be the right battery to use in my project?
Then what could be the right motor driver to connect all these motors?
I found adafruit motor driver suits well but I have some doubts on that. Will adafruit give high output to DC and stepper motors?
Suggest solution to solve my problem.
Firstly kg is not a unit of torque. What do you mean? kgf-cm?
If its kgf-cm then those values are 2Nm and 1.5Nm in SI units (always work in
SI units, this is the 21st century, not the 19th!).
Those are fairly large values, making me immediately suggest you should be looking
for gear motors(*).
Anyway before you proceed explain more carefully what your requirements are -
torque and speed (you need both to size a motor). Explain what you are going to
do with the motors (you may be going about things all the wrong way and end up
disappointed, less us help!)
(*) The torque of a gear-less motor is roughly proportional to its volume/weight,
motors are most efficient at certain speeds, gearing trades torque for speed.
Thank you for your response markT.
Sorry for my bad understanding of Electronics and my bad English. I am very new to this field. I am searching every answer in internet. I don't know about Nm and SI units and all. I'll try to explain briefly once again with my best knowledge.
Actually I am going to build a Robot with Wheels. Four wheels with high torque geared motors. That four motors are with 20Kgf-cm torque and 500rpm speed. Another Stepper motor with 15kgf-cm torque I don't know about stepper motors speed. Then two servo motors of 5kgf-cm torque.
With all these setup I need a battery backup of minimum 5 hours. If I use high Ah batteries Will the Arduino board get affected?
Then I use bluetooth module and 6 ultrasonic sensors with my project.
Thanks in Advance.
abish_r01:
Thank you for your response markT.Sorry for my bad understanding of Electronics and my bad English. I am very new to this field. I am searching every answer in internet. I don't know about Nm and SI units and all. I'll try to explain briefly once again with my best knowledge.
Well time to learn then, basic mechanics is fundamental to robotics, newton is
the unit of force, newton-metre is the unit of torque. 1 newton-metre times 1 radian/second
is 1 watt of mechanical power, simple.
Actually I am going to build a Robot with Wheels. Four wheels with high torque geared motors. That four motors are with 20Kgf-cm torque and 500rpm speed. Another Stepper motor with 15kgf-cm torque I don't know about stepper motors speed. Then two servo motors of 5kgf-cm torque.
Those four motors are 2 Nm and about 50 radians/second, or 100W output power, so
perhaps 120 watts in at full pelt. That's a lot of power, 0.5kW peak for 4 motors.
Yes, you will need high power and high capacity batteries, this is a traction
application....
With all these setup I need a battery backup of minimum 5 hours. If I use high Ah batteries Will the Arduino board get affected?
Why do you think the motor battery capacity has anything to do with the Arduino? You
won't be powering the Arduino from the traction battery if you want an easy life...
Then I use bluetooth module and 6 ultrasonic sensors with my project.
Excuse me, if I misplaced any words. Thanks in Advance.
Thanks markT.
Surely I will try to learn little mechanics needed to robotics.
Those four motors are 2 Nm and about 50 radians/second, or 100W output power, so
perhaps 120 watts in at full pelt. That's a lot of power, 0.5kW peak for 4 motors.
Yes, you will need high power and high capacity batteries, this is a traction
application
If I use L298 motor controller. it will produce at max of 3Amps per motor. Then why should I go for that much huge battery(0.5kW power). Actually I am not going to load weight on robot. But, my default weight of robot is around 20 to 25kg.
As I said earlier, I am using 20kgf-cm four motors to move around and 15kgf-cm inside the robot for shaft(ie, to increase and decrease the height of robot from 3feet to 5feet and vice versa). Then at top finally two motors for pan and tilt. that's it. I am confused totally how to build the model of robot. Can you please suggest how to make this all work, with some sample pictures or something else?
Then suggest, what motors are the best choice and what motor drivers can be used and what battery needed for my project with some links.
Why do you think the motor battery capacity has anything to do with the Arduino? You
won't be powering the Arduino from the traction battery if you want an easy life
Actually, I used 4.5Ah battery to run my old project. My Arduino gets heated in a radius of 1.5cm from the external power plugging jack in UNO board. That's why I asked.
Can you show me some shaft mechanism links to increase and decrease the height of robot and for panning and tilting the head part of robot? What length and breadth needed to handle this 4feet height?
It is very helpful if you provide ideas to me. Thanking you once again markT.
You quoted a motor of 2Nm and 500 rpm - that is 100W, that's the laws o physics.
If you limit it to 3A and 12V then it cannot be giving both 2Nm and 500rpm, fact.
Perhaps some data would be good:
What maximum speed of travel?
What diameter wheels?
Mass: 25kg or so we know
What maximum incline do you want it to handle?
Other requirements?
Thank you markT.
You quoted a motor of 2Nm and 500 rpm - that is 100W, that's the laws o physics.
If you limit it to 3A and 12V then it cannot be giving both 2Nm and 500rpm, fact.
Ok. But if I use L298 motor controller it only produce at max of 3A. Then what motor driver produce that much output to run my motors?
- What maximum speed of travel?
- What diameter wheels?
- Mass: 25kg or so we know, What maximum incline do you want it to handle?
- Other requirements?
Please suggest me.
Then, I guess you are going to answer(suggest) my previous threads question also.
abish_r01:
Thank you markT.Ok. But if I use L298 motor controller it only produce at max of 3A. Then what motor driver produce that much output to run my motors?
Do not start by choosing the motor driver, you start with the physics/mechanics, determine
the motor/gear system and its rating, then you find an actual motor that is good enough, and
only then can you choose a motor driver!
Otherwise its like you've bought a lawnmower engine (say) and ask how to make a sportscar with it!
- 400-500 rpm is the max speed of travel
That's a rotation speed, not a speed of travel.
- 4 inch to 6 inch diameter.
500 rpm and 15cm diameter wheels means you want this thing
to go at about 4m/s (9 mph) is this right?
- Yes, at max of 25 kg is the total components weight, my robot is going to handle.
- For stepper motor also I planned to use L298. Is that a right choice?
No, not for 500rpm, why would you want a stepper motor, they are inefficient.
- If I use three wheels instead of four, will my robot move(turn left and right) with the weight of it. For reference I attached the three wheel concept image below.
Please suggest me.
Then, I guess you are going to answer(suggest) my previous threads question also.
So we have established the speed over ground only, no idea how much power you
need as you've said nothing about max incline.
Let me assume light indoor use, say a max incline of about 1 in 10, then the
force at the wheels is 250N / 10 = 25N, shared between two wheels is 12N,
so the torque needed per wheel is 0.9N, add a large safety factor of 1.5 or 2
and you're at the 2Nm level (encouraging as you already had this figure).
But as I said that's 100W mechanical as 4m/s on a 1 in 10 incline is 0.4m/s
vertical rate, with a 25kg load thats 0.4m/s x 250N = 100W. However that
is for the entire vehicle, not per motor, and its presumably not continuous.
Maybe then we can assume such climbs are rare and derate the motor back
down to 1Nm or less for continuous duty. Lets say 0.5Nm continuous, peaking
at 1.5Nm. That's more like 25W per motor, peaking 75W.
So two DC motors, 12V, nominal 2A each, peak 6A each. No, L298 will
not work here (unless you go to 24V and 1A motor, peaking 3A)
MarkT:
So we have established the speed over ground only, no idea how much power you
need as you've said nothing about max incline.Let me assume light indoor use, say a max incline of about 1 in 10, then the
force at the wheels is 250N / 10 = 25N, shared between two wheels is 12N,
so the torque needed per wheel is 0.9N, add a large safety factor of 1.5 or 2
and you're at the 2Nm level (encouraging as you already had this figure).But as I said that's 100W mechanical as 4m/s on a 1 in 10 incline is 0.4m/s
vertical rate, with a 25kg load thats 0.4m/s x 250N = 100W. However that
is for the entire vehicle, not per motor, and its presumably not continuous.Maybe then we can assume such climbs are rare and derate the motor back
down to 1Nm or less for continuous duty. Lets say 0.5Nm continuous, peaking
at 1.5Nm. That's more like 25W per motor, peaking 75W.So two DC motors, 12V, nominal 2A each, peak 6A each. No, L298 will
not work here (unless you go to 24V and 1A motor, peaking 3A)
:') its just...so beautiful...
There's also the battery weight to consider - are those 25 Kg accounting for the battery weight as well? Also - where does that figure come from? Is this a school project (or similar) with a fixed set of requirements, or is it something you are designing for personal (or other) use?
The thing is, it is possible to get into a weird "death spiral" - where you are increasing the size of the battery to keep up with the size of the motors to keep up with the size of the mass of the robot - and increasing the size of the battery increases the mass of the robot - and round-n-round you go!
Which is why you need to start with the battery and motors, plus your base numbers - then work out your power and mass budget for the needs of the robot; this will give you the numbers you need to know what surplus weight/mass you can move.
When things are sized properly - you can move a lot for a long time (power wheelchairs being a prime example of what can be done when engineering and design are done properly).
Battery capacity and endurance is a separate issue!
Thanks markT & cr0sh.
Max incline(slope) is 15 degree, measured by protractor.
500 rpm and 15cm diameter wheels means you want this thing
to go at about 4m/s (9 mph) is this right?
I don't know these much calculations included in my project. I need to run the robot in a open surface with some moderate speed. So I didn't research too much on that.
No, not for 500rpm, why would you want a stepper motor, they are inefficient.
I need to stop the shaft in a accurate position. So I chosen the stepper.
There's also the battery weight to consider - are those 25 Kg accounting for the battery weight as well? Also - where does that figure come from? Is this a school project (or similar) with a fixed set of requirements, or is it something you are designing for personal (or other) use?
The weight of robot is 25 kg, including the battery weight of 5 kg(approx). Then the front wheel procedure I saw in youtube and planning to include in my project to reduce a motor.
To start designing only I am asking this all. Then need to make a plan and start work.
You need encoders on your motors or wheels. Stepper motors for traction will waste
most of your battery capacity. DC motors only pull the current needed at the time,
steppers pull their maximum current all the time and aren't really suitable for traction (yes
they are used in little robots for convenience, but you need to consider your battery
capacity).
Sorry for the late response markT.
You need encoders on your motors or wheels. Stepper motors for traction will waste
most of your battery capacity. DC motors only pull the current needed at the time,
steppers pull their maximum current all the time and aren't really suitable for traction
Ok. You said about many calculations to be considered in my project. Still you didn't say were to get right motors and what battery should be suit to my project and all. (Lead acid, lithium and many are available)
Special Thanks markT.
This isn't a procurement service! Also without knowing which territory you are
in its hard to recommend suppliers.
Work out the actual power speed and torque you require and then have a look
on eBay perhaps? There's quite a range of DC motors and gear motors there
these days.
hi guys. i have found very handy information in this thread. thanks for such important discussion.
