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prashant_chhonker
09-17-2006, 01:04 AM
I am building a wall climbing robot. It is a tracked vehicle(like packbot, talon) but when it encounters vertical surfaces in its path, it shifts to its wall climber mode.

I have finished a proof-of-concept vehicle. Now, I am planning to build a functional prototype which I can show to the interested parties(companies, VCs, etc) as a product. As this would be the final design, I am taking extreme caution in buying the components for the same, especially the drive motors. I need your advise for the same.

This is a wall climber so, the weight of the robot is critical. The final machine along with its payload would weigh 40 kgs Max. I am designing the robot with this weight specification. The weight of robot and payload could be traded with each other. This makes the selection of the right motors along with the gear boxes absolutely crucial. I have not been able to find a reasonable buy till now. I have checked markets like Lajpat Rai, Chawri Bazar, Mayapuri, Jhandewalan etc(all are located in Delhi). with no success. Most of the motors that are on sale are industrial in nature and unfit for robotics use.The best solution so far is the rotomag AB2-R with 148 kg-cm torque. The link is http://www.rotomag.com/PM3.htm. But this motor along with the gearbox is heavy(6.5 kg). The dealer was asking Rs 7,200 for it which is not very less than the imported ones with the same specification. Importing motor along with their gearboxes is prohibitively expensive. But, I would buy them if nothing works.

Someone, please suggest a better alternative(price, places to look for, ratings)? I would be thankful(infact grateful) for the same.

Motor(attached to its gearbox) requirement specification is:

No. of Motors : 2
Weight : 4kg(Max)
rpm : 30-50
voltage : 12-24 volts (Note: I will over volt them )
Torque : 120+ Kg-cm
HP : Any horsepower that satisfies above specification is ok.
Email : prashant_chhonker@yahoo.com

Regards
Prashant Deep Chhonker

P.S. : Any suggestions regarding above is welcome and appreciated

sas87
09-17-2006, 08:55 AM
Hello,
We have made a Wall Climber project under our mentor docel since 2 yrs. We have presented our paper with the working model in several colleges last year like BMSCE, BIT, PESIT etc.,

Our climber is aout 3Kgms. It is very difficult to maintain this Bot on the wall even with that weight.
How do you manage a 40Kg climber on the wall??? We thionk it is very difficult to manage this :!:

sas87
avibond
nag99
robcop

vikas
09-17-2006, 11:55 AM
Have a look at this

http://www.pololu.com/products/tamiya/0070/

Produces 15kg of torque at 400:1 gear ratio.Gear Ratios: 4:1 5:1 16:1 20:1 25:1 80:1 100:1 400:1.Motor: RE-260
RPM: 5040-6300 (5040 Max. Efficiency)
Voltage: 1.5-3V (1.5V Recommended) (4.5 V max)
Amperage: .64A
Stall torque: 15 gcm

But i would love to ask the same question as sas87 has asked.

prashant_chhonker
09-17-2006, 03:52 PM
Hello everyone



sas87 wrote:
How do you manage a 40Kg climber on the wall??? We thionk it is very difficult to manage this.


Yes sas87, your observation is correct. Making 40kg wall climbers is an extremely complex task. But it is very much possible. I am saying it after doing it. The proof-of-concept(POC) vehicle can carry this amount easily(40kg includes it's own weight as well). The bigger challenges are ground to wall and wall to ceiling transitions. Imperfections in real world vertical surfaces (like crevices on walls, curvatures) is another big issue.
POC's maneuverability is not up to the mark. I wish to correct it in the final product.
I am writing an article on wall climbing robots. It should be ready by tommorow. Would address all the issues in it.

Prashant Deep Chhonker

allbits
09-17-2006, 05:56 PM
hi..


just curious..

but i would like to know what type of wall(i meant the surface) do you plan? and what type of gripping do you have? is the prototype meant for real life situations?

any way it will be great to see a 40 kg payload up on the wall.

Supario
09-17-2006, 09:33 PM
What about if it falls off ?

sas87
09-18-2006, 09:55 AM
Good question danger if it falls.
Wall climbers are to replace and avoid danger to humans. 40kgs from a height will be fatal, if it hits anyone. Lots of power is needed to keep the bot attached to the wall. as [/b]allbits asked, it cannot be a "gripping" [b]Robot.
The gripping involves microclaws and not easy to make. Walls are different even in the same construction practice. A rough wall will need a particular mechanism which will fail if granularity varies. all the mechanisms of grippers are patented and very costly.

Active Grippers need heavy torque and must be driven by heavy motors. The range of such climber will be very less due to excessive power drain. PM3 motor will not be able to handle the force of gravity which will present downward pull of the weight. The maths and physics will not agree. minimum size of granules on wall willl should be 2mm if the gripper has to stay on the wall. If using welcro type gripper, then the size of grippers should be minimum 200 times the granules needed for grip. this is passive gripper and cannot be dynamic.

This is our experience and we have dome a lot of work on the Climber. We are still struggling , after 2 years of very hard work :cry:

prashant_chhonker
09-19-2006, 02:10 AM
Thank you everyone for the response.


but i would like to know what type of wall(i meant the surface) do you plan? and what type of gripping do you have? is the prototype meant for real life situations?


I am designing this machine for fire-fighting and military purposes (not for home or industrial use) and plan to sell it commercially. So, it should and would be able to climb surfaces like walls, wood, glass etc.


Good question danger if it falls.
Wall climbers are to replace and avoid danger to humans. 40kgs from a height will be fatal, if it hits anyone.


Sas87, many thanks for sharing your experiences.

Yes, even a 3 meter fall would be fatal for the machine and any human that happens to come in the way. But, all engineering systems are designed with certain tolerances and whenever they are exceeded, accidents happen (like in case of aircrafts, cars even computers).
Anyway, I am designing this system for fire-fighting and military purposes (these are emergency situations). Accidents can be avoided by planning operations before hand.



“Our climber is about 3Kgms. It is very difficult to maintain this Bot on the wall even with that weight.
How do you manage a 40Kg climber on the wall??? We thionk it is very difficult to manage this ”


First of all let me tell something about my robot.
Vacuum based suction is the primary mechanism through which the robot would stick on the wall.
Let's briefly discuss the theory behind this mechanism:

Atmospheric pressure is the pressure above any area in the Earth's atmosphere caused by the weight of air. Standard atmosphere (atm) is a unit of pressure and is defined as 1.033 227 452 799 886 kg-force/cm2.This tells us that 1 cm2 area will experience a force of 1kg if it has vacuum on one side and atmosphere on another. Similarly 100 cm2 area would experience 100kg and so on. All the suction based wall climbers use this force to generate friction (or grip) between gripper and the vertical surfaces.

Reference: http://en.wikipedia.org/wiki/Atmospheric_pressure

This tells us that larger the surface that holds the vacuum, the larger would be force on it. Higher force means increased friction and better grip. The total area under the grippers of my robot is 300cm2 . I think this answers the query, how 40 kg can be supported on the wall.

In case, the primary suction mechanism starts to fail (due to reasons like crevices, sharp curvatures, obstacles, smoothness or lack of it etc.) another drill based gripper mechanism kicks into action. This drill based backup provides exceptionally reliable grips on the wall (just drill a hole with a battery operated hand drill and put a nail inside and see how much weight can a single nail sustain before it bends or before the plaster comes off).


PM3 motor will not be able to handle the force of gravity which will present downward pull of the weight.
PM3 motor is absolutely useless as far as robotics is concerned (may be find some use in an industrial robot). By posting information about it, I wanted to tell that I couldn’t find a better one.

Regards
Prashant Deep Chhonker

P.S.: I cannot discuss the design details because of IPR issues.

sas87
09-19-2006, 06:15 AM
Well that explains. We are using similar techniques. We are building fail-proof systems which will take the payload to 6kgs max.
But drilling may be a problem before losing grip. The drill will try to push the vehicle away from the wall. But 40 kgs is still toomuch!

prashant_chhonker
09-19-2006, 11:01 PM
Hi


But drilling may be a problem before losing grip. The drill will try to push the vehicle away from the wall.

As I mentioned in my earlier post, the area under the vacuum is 300 cm2. This gives me a combined downforce of 300kg on the surface of the grippers. This translates into the 300 kg force on the robot itself. Out of these 300kgs I can take few kgs of force to drill effectively(no issues).


Well that explains. We are using similar techniques. We are building fail-proof systems which will take the payload to 6kgs max.



But 40 kgs is still toomuch!

Well, let's say you acheive your 6kg target. Then make 7 copies of your robot and combine them to get a total payload of 42kgs!!! :)
By above, I mean that design, size and other factors decide the final payload.
Sas87, can you send me the final report you made for the colleges. I would be able to answer your queries in a better way.

Prashant Deep Chhonker

allbits
09-20-2006, 12:05 AM
Hmm...


i always hate equations when it comes to robotics because you design a robot with equations only to know that it is practically impossible.

But now let me come to the point.. I have not done homework on force distribution(ie, please correct me if i am wrong), but all the atmospheric pressure will not come on the bot. Only the horizontal component will be acting on the bot. The vertical component+our good old gravity will be pulling our bot down.. we have to subtract these vectors

we assume Pa is the same in all directions at near ground conditions for the sake of simplicity. But eventhen,
F=mg , ie 40*9.8 that will be approx 400N is going down!!

This, F = ma is defined for a point body. Now if you have a bot with weight distributed, and if the center of mass is placed at a point away (which will be atleast 10cms from the gripper), you can calculate how much more power is needed in terms of grip.

So, our gripper must have, practically a near perfect vacuum generation, or if you plan to use drillers, you will have to add some redundancy in the form of extra grippers, or larger feet sizes.

Please ignore this post if you have designed the req motor torque and the shape/gripper design considering all these.

I do still believe this is possible, because :

40 kg + 16 kg = approx my weight!!
there are some good vacuum grippers (but for glass surfaces) you can use which can carry your weight!!

but still,... you have to overcome a lot of huddles.. Best of luck !!


PS:

Equations does not always work not because they are dumb, its because we always forget the environment in to which these equations were designed for. We all do, dont we?? :D

sas87
09-20-2006, 01:12 PM
Hi
[quote]
Well, let's say you acheive your 6kg target. Then make 7 copies of your robot and combine them to get a total payload of 42kgs!!! :)
By above, I mean that design, size and other factors decide the final payload.

Prashant Deep Chhonker

:?: How??

Have you tried lifting 40kgs- using motors?? I find it difficult to lift it myself 8O

Lot of sense in what you say allbits. most of us think a 40 kg weight can be lifted by applyiing 40kgs opposite force.
...we still think 40kgs is impossible.

Have you REALLY tried it?

satya
sas87

prashant_chhonker
09-21-2006, 04:09 AM
Equations does not always work not because they are dumb, its because we always forget the environment in to which these equations were designed for. We all do, don’ we??

I agree with you. We usually don’t take a holistic approach while applying equations.



I always hate equations when it comes to robotics because you design a robot with equations only to know that it is practically impossible.

Equations are avoidable in small robots. I don’t recommend using them in small robots either. But in big ones like the one I am making, they are important. For example, I cannot put grippers on some platform and put it on the wall and see if it sticks. Grip, weight etc. has to measured and incorporated into design if any wall climber project has to succeed.

A little advice:
In robotics, it is friction that spoils the party for equations (generally). I suggest you consider friction as a parameter in your equations (or rather calculations). This gives a very realistic estimation of the final performance.
Learn to USE maxima-minima and principles of Linear Programming. They are valuable during the design phase of big machines. They have been instrumental in my decision making and I use them when I select components, design a part, optimize weight distribution of components in the machine, etc. To top it all, it is the basic equations that do the trick. No fancy maths required.



Please ignore this post if you have designed the req motor torque and the shape/gripper design considering all these.

I have considered all the above issues (and more) in my initial design. Well, working on them and implementing them is another story. Allbits, I appreciate your understanding of wall climbing robots.


Have you tried lifting 40kgs- using motors?? I find it difficult to lift it myself
One can lift any amount of weight by using motors. Take a look at the motors mentioned below.
http://www.robotmarketplace.com/marketplace_magmotors.html



...we still think 40kgs is impossible.

Well, impossible is sitting next to my computer table.:-)


Vikas, I have purchased two motors from Lajpat Rai Market. They look good for the time being. Would import better ones, if things don’t work out.

I plan to finish the product version of my machine in the next 3 months. I will be active on forums then.

Thanks and regards to all who have taken time to read my posts and those who have provided suggestions.

Prashant Deep Chhonker

allbits
09-21-2006, 01:25 PM
All the best.. i can wait more than 3 months to see an indian effort in india to put 40 kg up on the wall.. only thing i wish the components were all indian...

and something also reminds me of Docel's signature..... :)
(please dont mis-take me on this comment)

dulu
10-26-2006, 02:30 PM
hello frend ,
i also make robos , but till nw i had not yet made robos of such weight . i buy motors from mumbai , so i tell u to have a look in mumbai market . and one thing i want to know that wht is the required speed for ur robo ? accordingly motors should be used .
thank you .

allbits
12-13-2006, 06:54 PM
3 months...

whats up man??? :?:

docel
12-13-2006, 10:59 PM
:lol: :lol: ....Now, Come on Allbits :wink: :wink: Are you serious?!!?

Just imagine THIS http://www.robotmarketplace.com/marketplace_magmotors.html

.....doing THAT!! :lol:

shashak
12-14-2006, 12:16 AM
after seeing this i wish i have a swiss bank account :cry:

but till then i am waiting for them to be available in Indian market
:lol: :lol: :lol: :lol:

docel
12-14-2006, 01:06 AM
Shashak...YOU DONT NEED THOSE motors!!!
They are just "show offs" for effect rather than something to be used.
Dont get carried away by the maths. They are a little stranger than fiction, as far as Laws of Physics and Engineering ( or the lack of it :wink: )
We have made it with some very sober motors and didnt have to use those monsters!!!

shashak
12-14-2006, 01:18 AM
I I Captain :D

allbits
12-14-2006, 10:48 AM
what made you think i was serious...
:evil:
:lol: :lol:

but i didnt want to be sarcastic either..
but he made a statement.. i would appreciate if he at least turned up ....

prashant_chhonker
12-14-2006, 11:01 PM
Hi allbits



what made you think i was serious...
:evil:
:lol: :lol:


but i didnt want to be sarcastic either..
but he made a statement.. i would appreciate if he at least turned up ....


Can you please explain, what do you mean by that?

Prashant Deep Chhonker

allbits
12-15-2006, 09:16 AM
c'mon man.. its so obvious.. do i need to explain??? :?:

docel
12-15-2006, 10:04 AM
wELL, alLBITS....SOMETIMES YOU'LL HAVE TO S P E L L things out, I guess :wink:

To translate- We are waiting, at the end of 3 months, to see this 40Kg. Wall climber on the wall :!: and to learn some new concepts of Physics from you.

We are also curious to know if it is still sitting next to your computer or 'hanging' on the Wall.

prashant_chhonker
12-15-2006, 10:20 AM
Well then what can I say?

Looks like people here have a way of handing out verdicts about other people's work without having a clue about what they are talking about. On top of that they choose not to appreciate others but make scathing remarks.

Well in any case, here is a wall climbing system that can raise upto a ton which is upto 25 times of what i am planning to do(and have done that).
http://www.gizmag.com/go/1547/
http://www.oxfordstuntfactory.com/html/BBC%20News%20%20SCI-TECH%20%20Suck%20it%20and%20climb.htm

I wonder how people on this forum would have treated Gerald Winkler, if he had come to roboticsindia in his project conceptualization phase. :(

As far my wall climber is concerned, the mechanical part has been completed. But the electronics area, especially the motor controller is still under development.



wELL, alLBITS....SOMETIMES YOU'LL HAVE TO S P E L L things out, I guess

To translate- We are waiting, at the end of 3 months, to see this 40Kg. Wall climber on the wall and to learn some new concepts of Physics from you.

We are also curious to know if it is still sitting next to your computer or 'hanging' on the Wall.


Mr. docel you never participated in this thread before. Never given any suggestions. You don't know me. Don't have a clue about how I plan to acheive my said objectives. But you are bold enough to issue such insulting remarks.

Seeing such behavior I call quits on this forum.

Prashant Deep Chhonker

docel
12-15-2006, 10:39 AM
...just what I expected!

allbits
12-15-2006, 05:57 PM
i really, really apologise for putting fuel into dead fire.. but i was so curious ...
didnt mean to have an end like this...
:cry:

and prashant, i appreciate you for turning up, but i do not appreciate when you quit because you found some one (including me) insulting to you. I'm just a humble user... I would be very happy if you could complete ur idea faster, because u have a point to prove...(to us, who didnt quite accept your idea!!)

Its not about fighting, and calling it quits.. its about fighting and not quitting.