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Topic: Help with parts for a full size balancing robot (Read 1 time) previous topic - next topic

Lauszus

Apr 11, 2012, 08:51 pm Last Edit: Apr 13, 2012, 02:52 am by Lauszus Reason: 1
Hi guys,
Just a month ago I finished my mini balancing robot: http://blog.tkjelectronics.dk/2012/03/the-balancing-robot/

http://www.youtube.com/watch?v=N28C_JqVhGU

And now I would like to build a full size one, but I need some help for some parts.

The only thing I have right now are the microcontroller (mbed - http://mbed.org/handbook/mbed-NXP-LPC1768), XBee modules (for wirelessly debugging) and a 6DOF IMU - which are all parts I also used for my mini segway. I will also use an Arduino ADK for communication with my Android phone.

I also got some geared motors from an electric wheelchair, but I'm not sure if they would do the job - I would really like to know the opinion of some of the experts around here :)

The specs for the motors are:
Supply Voltage: 24V
Maximum current: 3.9A
Watt Output: 60W
RPM: 90rpm (2000rpm without gearbox) - it's a 22 ratio gearbox
Torque: 3.4Nm

The full name of the motors are: "Parvalux REF PM 3MB/511592/2B2" - I have no idea what the numbers after 3MB means (3MB are the specific motors and gearbox).
Here is the datasheet for the motors: http://blog.tkjelectronics.dk/wp-content/uploads/ParvaluxMotorSpecs.pdf

The main thing I am worried about is the rpm, as I am not sure if they are fast enough for a balancing robot, but I have seen a lot of people building full size balancing robots with wheelchair motors, so I think they are allright?

I also need a motorcontroller, 24V battery - maybe 36V to make it go faster, some pneumatic wheels (something like these: http://www.northerntool.com/images/product/images/1330_lg.jpg), and some wheel hubs for a key mount.

I would also need some quality cables, connectors, and some basic stuff like that, that can handle the current.

I am thinking about ordering everything from Robot Marketplace: http://www.robotmarketplace.com/store.html
And I have already made a post on there forum, but no one has never answered me: http://www.robotmarketplace.com/forum/viewtopic.php?f=5&t=303&p=795

Hope somebody out there can help me.

Best Regards
Lauszus

robyc

In the arduino robotics book written by John-David warren there is a segbot project on which I am working.
I don't know If this can help but I bought 2 second hand wheel chair wheels and motors from a local store and took the brakes off.
For the motor controller I ordered a sabertooth 2x25 from www.dimensionengineering.com.
I could not find a 6 dof Imu (where did you buy it?) so I ordered an accelerometer and a gyroscope from the arduino store (tinker) together with an arduino UNO.
These products have not yet been delivered so I have not been able to try them out....yet.

Lauszus

#robyc
Thanks for your reply.
I also heard many good things about the Sabertooth motordriver. It is also very versatile.
I use the following IMU: http://www.sparkfun.com/products/10010 for my mini segway, but I think I will order one with a lower resolution for this project, as +-3g accelerometer and 300deg/s gyro is a bit to much - I think +-1.5g and 50deg/s would be sufficient for my needs.

You should see my other post at the Arduino forum, if you are new to IMU's: http://arduino.cc/forum/index.php/topic,58048.0.html

Regards
Lauszus

robyc

Hi Lauszus.
I must admit I wasn't able to understand all the details you posted but I found your mini balancing robot very interesting. Great job!
I was also looking for 10 inch wheels and your video solved the issue (with www.northerntool.com).

The 6 dof Imu on sparkfun has been "retired" and I could not find it on watterott.com either. I guess I will stick with the tinker-arduino version hoping it will work....
I will probably be back with further questions once I have studied your Imu link.
Ciao.
Roberto

Lauszus

Hi,
Thank you :)

I know, but I think anything like that would be alright!

Regards
Lauszus

tmarkson

Quote
Just a month ago I finished my mini balancing robot: http://blog.tkjelectronics.dk/2012/03/the-balancing-robot/

And now I would like to build a full size one, but I need some help for some parts.


Lauszus, Your mini balancing robot is fantastic! The control looks smooth and all of your peripherals seem to work well together. I admire your libraries for mbed and Arduino - I'll be using those in my projects soon enough.

What size are we talking about? Do you want to ride this larger robot? Any requirements for runtime and terrain capabilities?

Quote
The only thing I have right now are the microcontroller (mbed - http://mbed.org/handbook/mbed-NXP-LPC1768), XBee modules (for wirelessly debugging) and a 6DOF IMU - which are all parts I also used for my mini segway. I will also use an Arduino ADK for communication with my Android phone.

I also got some geared motors from an electric wheelchair, but I'm not sure if they would do the job - I would really like to know the opinion of some of the experts around here

The specs for the motors are:
Supply Voltage: 24V
Maximum current: 3.9A
Watt Output: 60W
RPM: 90rpm (2000rpm without gearbox) - it's a 22 ratio gearbox
Torque: 3.4Nm

The full name of the motors are: "Parvalux REF PM 3MB/511592/2B2" - I have no idea what the numbers after 3MB means (3MB are the specific motors and gearbox).
Here is the datasheet for the motors: http://blog.tkjelectronics.dk/wp-content/uploads/ParvaluxMotorSpecs.pdf

The main thing I am worried about is the rpm, as I am not sure if they are fast enough for a balancing robot, but I have seen a lot of people building full size balancing robots with wheelchair motors, so I think they are allright?


Motor choice in this application depends on how fast your robot might fall forward (or backward). The fall speed of a balancing bot is dependent on center of gravity and total mass. Robot's ability to compensate for fall is determined by wheel RPM, wheel diameter and torque.

First step would be to over estimate total robot mass and size. These are determined by robot specification - see questions in second paragraph of this post.

Next, when you have a reasonable location for center of gravity, estimate how fast that mass might fall. Include any possible outside forces in your calculations here.

Finally, you should have a rotational speed. This could be an angular velocity of the CG in relation to the wheel centers.

If you would rather not do math, simulate the entire robot system with wood and weights using your best judgement of position and weight of payload groups. Time how long it takes for your simulated robot to fall from vertical to horizontal (or some number of degrees). That's your angular velocity, sum your components to get a total mass, and this becomes the worst case to design against.

Convert the angular velocity to rotational speed of your axle and compare to your 90RPM for wheel chair motors. I'm happy to help with the simulation/calculations if you can give more detail on your robot system requirements.

Quote
I also need a motorcontroller, 24V battery - maybe 36V to make it go faster, some pneumatic wheels (something like these: http://www.northerntool.com/images/product/images/1330_lg.jpg), and some wheel hubs for a key mount.


Robot marketplace has a great selection of batteries and motor controllers. Again the system specs will give you a minimum requirement for runtime and motor current/control protocol.

Andymark has $40 8" pneumatic wheels (http://www.andymark.com/product-p/am-0970.htm?CartID=2) and key hubs (http://www.andymark.com/product-p/am-0077.htm).

Quote
I would also need some quality cables, connectors, and some basic stuff like that, that can handle the current.


I use powerpoles for power wiring. Other options are automotive terminals, such as ring or butt crimps. For any crimps you use, get the correct crimp tool. Robot Marketplace or Powerwerx has powerpoles.

For signal wiring it depends on the application. Some options would be pin headers (such as those on end of servo), D-sub connectors (like DB9 or DB25), Centronics, molex, microphone (DIN) connectors, RJ11 and RJ45. I prefer using IDC connectors with ribbon cable for signal connections that need not be shielded. For the few shielded applications I've needed, I used DIN connectors. http://www.allelectronics.com/ is a great supplier for bulk items.

I recommend an enclosure to house your control system. Bring the signal and power connections to one place on your box and mount everything within using fasteners or velcro. Your use of pin jumpers and breadboards on mini balancing robot was effective but dangerous for the system.

Quote
I am thinking about ordering everything from Robot Marketplace: http://www.robotmarketplace.com/store.html
And I have already made a post on there forum, but no one has never answered me: http://www.robotmarketplace.com/forum/viewtopic.php?f=5&t=303&p=795


I saw your post on their forum. I'm still waiting for my account to be validated. I came across your post on this forum after searching for your motor. Lucky  ;)

Ted

MarkT



I would also need some quality cables, connectors, and some basic stuff like that, that can handle the current.



RC model connectors are very compact, pretty cheap and high current - you have to solder them to the ends of wires and heat-shrink a sleeve on, not as simple as crimp connectors but take up less space.  If you can afford/find silicone-insulated finely-stranded cable it will be the business (easy to work with because very flexible, can use thinner wire as it tolerates self-heating better).

Lovely little robot by the way ;)

Your comment about the speed of the motors intrigues me - I would have thought its the "speed" at which a motor can develop torque is the important point, which depends on the motor controller and the back-lash in the gearing more than anything.  A delayed response to control input is going to make the control loop much harder to stabilise.  Surely the rpm simply limits the speed the robot can go, not the stability?
[ I won't respond to messages, use the forum please ]

Lauszus

@tmarkson
First of all - thanks for such a detailed reply, I was worried that no one would ever reply ;)

Quote

What size are we talking about? Do you want to ride this larger robot? Any requirements for runtime and terrain capabilities?


Yes I would like to build a rideable one. I think the runtime should be at least 30 minutes for it to be any fun. And it should be able to run on any hard surface - I don't think I will ride it in any terrain except maybe grass.

I haven't tried to simulate the robot yet, but I have done some basic calculations with a total mass of 90kg and a wheel radius of 8cm. You can see them in the attached pdf.

I haven't done any drawings of the robot yet, but I will try to do it and then - with your help hopefully - calculate the specs of the robot :)
I won't do it this week, as I'm very bussy at school, but next week I will try to make a drawing and then do some calculations.

I think that 8inch diameter wheels are a bit to small, I was thinking about more like 15inch - maybe I will just use wheel tires. Or what do you think?

Thanks for the advice regarding wires, connectors etc.
I will suddenly make it fit inside a enclose, as you can seriously get hurt it it suddenly fall over if a wire gets pulled out. Right now I thinking about making a custom PCB for my balancing robot too, so i looks more finished, and just not like a prototype.

I actually had to email robotmarkedplace, because they hadn't validated my account after a week.

@MarkT
Thank you for your advice - especially on those silicone insulated cables. I were also thinking about using XT60 connectors, as I have heard many good things about them - I'm currently changing those tamiya connectors on my mini balancing robot.

You are totally right, but I just thought 90rpm sounded very slow compared to those motors (http://www.pololu.com/catalog/product/1443) I used for my mini balancing robot, as they had a run speed of 350rpm.

Regards
Lauszus

tmarkson

Quote
Yes I would like to build a rideable one. I think the runtime should be at least 30 minutes for it to be any fun. And it should be able to run on any hard surface - I don't think I will ride it in any terrain except maybe grass.


Right on, we can make some more assumptions using these specs. You can get a battery based on calculation using motor draw and runtime. DO that after you decide what motors will work for this project.

Quote
I haven't tried to simulate the robot yet, but I have done some basic calculations with a total mass of 90kg and a wheel radius of 8cm. You can see them in the attached pdf.


Calcs look good although I'm not sure where you got a couple of your constants. 8cm radius is a rather small wheel?

Quote
I haven't done any drawings of the robot yet, but I will try to do it and then - with your help hopefully - calculate the specs of the robot
I won't do it this week, as I'm very bussy at school, but next week I will try to make a drawing and then do some calculations.


Whenever you're able. Honestly the easiest way to go about this is to make a simulaid out of wood and add weights to it. There's no substitution for real world experimentation.

Quote
I think that 8inch diameter wheels are a bit to small, I was thinking about more like 15inch - maybe I will just use wheel tires. Or what do you think?


A smaller wheel will make it easier for the motors to compensate while balancing. The small radius produces more torque at the wheel and a smaller circumference requires less RPM to travel during adjustments. On-road applications don't require high ground clearance either.

However, if you expect to travel over road obstacles such as curbs and small animals, a wheel larger than 8" is necessary. A larger wheel will produce higher speeds.

Our mission is to find the wheel size and motor that will handle balancing and an appropriate speed.

PM me when you're not busy with school and we can work out the details. I'm interested in building a balance bot too - now is as good a time as any.

Ted

Lauszus

Quote

Right on, we can make some more assumptions using these specs. You can get a battery based on calculation using motor draw and runtime. DO that after you decide what motors will work for this project.


I will do that :)

Quote

Calcs look good although I'm not sure where you got a couple of your constants. 8cm radius is a rather small wheel?


Yes I know - the wheels on the electric wheel chair radius were only 8cm, that's why I originally used that in the calculations.

Quote

Whenever you're able. Honestly the easiest way to go about this is to make a simulaid out of wood and add weights to it. There's no substitution for real world experimentation.


Okay, I will try to build a wooden model in a 1:20 scale or something like that.

Quote

PM me when you're not busy with school and we can work out the details. I'm interested in building a balance bot too - now is as good a time as any.


Okay, I will send you a PM next week.

Regards
Lauszus

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