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### Topic: Selecting a motor for a DIY segway (Read 4186 times)previous topic - next topic

#### azizsm

##### Oct 23, 2015, 05:58 pm
How can I determine the power required for a segway. What are the parameters the can help me decide that?

For example I expect a person that weighs X and moves to a max speed of Y.

I want to choose 2 DC motors that can give the required power.

Thank you.

#1
##### Oct 23, 2015, 06:53 pm
Elektor magazine had nice series of articles on DIY Segway a couple of summers ago.
https://www.elektor.com/
You should see if you can get a copy of that, would be a great starting point.

Power = Force x Velocity
Force = Mass x Acceleration
Velocity = Displacement/Time
Power = Mass x Acceleration x Displacement/Time

http://www.physicsclassroom.com/class/energy/Lesson-1/Power

So how much power the motors need directly relates to the mass you are moving, how fast you want to accelerate, and how far you want to move it for how long.

Given all that, many people find electric wheel chair motors and 2 sealed lead acid 12V batteries work pretty well.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### MorganS

#2
##### Oct 23, 2015, 07:51 pm
Friction is a big part of the calculation. Do you expect to drive on grass or gravel? You may have noticed that 99% of all pictures of Segways show them on hard surfaces.

Speed is important for a balancing robot. It needs to have a software-controlled speed limit which is about half the maximum speed of the motors. This is so that it can 'catch up' to get the wheels back under you if you go too fast or downhill. That means you need to understand the RPM-per-volt characteristics of your motors too.
"The problem is in the code you didn't post."

#### azizsm

#3
##### Oct 23, 2015, 08:42 pm
Thank you CrossRoads I ll check that out, as for the power requirements, mass and velocity are the constraints that I design so it is easy to determine based on that. However, the acceleration is difficult to predetermine.

MorganS, the surfaces that I will drive on will generally be hard surfaces. For the speed, I am not really sure I understand why is it around half speed. Thank you.

#4
##### Oct 23, 2015, 09:21 pm
How fast do you want to change from 0 mph to top speed, say 5mph?  That is the acceleration. Neck-snapping fast, or a sloooow increase up there, while people walk by? I don't have a feel for what that number is.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### azizsm

#5
##### Oct 23, 2015, 11:40 pm
What about accelerations for balancing, inherently for balancing vehicles there is power being consumed constantly just for that. Is it insignificant compared to the moving power?

#### DuaneDegn

#6
##### Oct 24, 2015, 12:08 am
Here's another source of information.

Jason Dorie's Sideway skateboard style Segway.

#### MarkT

#7
##### Oct 24, 2015, 12:24 am
How can I determine the power required for a segway. What are the parameters the can help me decide that?

For example I expect a person that weighs X and moves to a max speed of Y.

I want to choose 2 DC motors that can give the required power.

Thank you.
Power = torque x angular velocity.

You need to determin the torque requirements and the speed requirements.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

#### MorganS

#8
##### Oct 24, 2015, 06:55 am
Why half speed? Consider what happens when your balancing thing is stationary. If it is tipped forwards by anything, then the motors must drive forwards to get the wheels back underneath the center of gravity.

The same thing happens when it's moving. If there's an upset that tips it forwards, the motors must accelerate to keep the balance. So the thing can never travel at the maximum speed of the motors because then it will just fall on its face.

One of the major upsets that is possible is rolling down a ramp. Even a very gentle ramp can very easily exceed the ability of the motors to drive the wheels back under the center of grabity.
"The problem is in the code you didn't post."

#### MarkT

#9
##### Oct 25, 2015, 03:46 am
Unless you live somewhere very dull and flat (like me!) you'd probably want to budget for a slope of 30%
or more anyway - that's going to set a rough value for required torque of 2Nm per cm of wheel diameter,
lets say 30cm diameter, so 60Nm (equivalent to 400N at the point of contact with the ground, enough
to push 100kg load up a 40% slope).   This is total for both wheels, note, so it would be 1Nm per cm of
diameter on each wheel.

60Nm or thereabouts means a gearbox or belt/sprocket reduction is mandatory for any chance of a
reasonable motor size.   30:1 reduction would be plausible, so 1Nm motors, which will be a few kg
each (motor torque and size/weight are strongly correlated).
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

#### jackrae

#10
##### Oct 25, 2015, 05:14 pm
I'd guess you might be looking at a pair of 400watt motors

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