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Topic: The gears, torque, and batteries OH MY! :'( [Heavy robot] (Read 1 time) previous topic - next topic

dritchie

Greetings,
    I'm currently working on a backyard tank robot with FPV. I could really use some advice from someone with engineering experience.

It's going to be about 1' square and almost fully metal. Roller chain, sprockets, thin case body. I want the robot to move at least at the rate of an average person's walking pace. I'm also targeting for a couple of hours of constant movement. And even longer while static.

Gear ratio to traverse an 45 degree incline
Motor torque to weight
Weight to battery lifetime

Motors I was planning on using:
https://www.servocity.com/html/3-12v_gear_motors.html
https://www.servocity.com/html/precision_robotzone_gear_motor.html

        If you have any insight I'd be glad to hear it :]
   

PaulS

Quote
It's going to be about 1' square and almost fully metal.
Tin? Lead? Copper? Titanium?
The art of getting good answers lies in asking good questions.

dritchie

Tin? Lead? Copper? Titanium?
Sorry if it appears I'm withholding info. It's just super early in development.

Aluminum Sprockets andi probably the body as well.
16 tooth - http://www.robotshop.com/en/aluminum-sprockets-16t.html
32 tooth - http://www.robotshop.com/en/aluminum-sprockets-32t.html

The chain will be steel. It is double strand.

Battery pack for reference: http://www.hobbyking.com/hobbyking/store/__11927__Turnigy_nano_tech_4000mah_3S_25_50C_Lipo_Pack.html I really want it to run a long time. But batteries weight a lot and I don't want to add a bunch of motors as that affects budget. I don't know how to decide on which :D Just looking for something in the middle of the two.

Arduno + xbee + small video transmitter. Motor controller board. hmmm. . .


zoomkat

Google forum search: Use Google Search box in upper right side of this page.
Why I like my 2005 Rio Yellow Honda S2000  https://www.youtube.com/watch?v=pWjMvrkUqX0

dritchie

You might consider modifying a large servos like below for continuous rotation to drive the tracks.

http://www.hobbyking.com/hobbyking/store/__18743__Vigor_VSD_11YMB_MG_HV_Extra_Large_360_Degree_Winch_Servo_0_75sec_40kg_150g.html
So the motors I was looking at have a max torque of 619 oz-in (or 17.5 kg) @12VDC. And that servo is 40 kg torque.

Consider it considered. Now what to make of this new info. :]

Edit: The more and more looking into it. The better it sounds. I found one video with one of these servos lifting 40 lbs with a gear.

dritchie

I've gone through and calculated the weight for the base components or what is in the pictures.

Rounding everything up I get 3.5 lbs total. So I'll target 5 lbs. But that is without the batteries, which weigh is 0.1 lbs each. I'm thinking something maybe x4+.

If I go with a 40 kg servo and a 16 tooth sprocket for the drive portion of a track do you think that would be enough "umpf?" :D (The scientific word)

dritchie

http://www.robotshop.com/blog/en/drive-motor-sizing-tool-9698

keeper63

I'm not sure how far you'll get with just the chain - take a look at this site for ideas on treads and other things.

I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

dritchie

I'm not sure how far you'll get with just the chain - take a look at this site for ideas on treads and other things.


I would appreciate it if we could keep focus on the question at hand. It hasn't been figured out and I'm settled on the design in that aspect.

But for you, I have looked at that site. In addition, to reading up on many different types of robotics tread systems that can be found online for several weeks before choosing chain. There is a reason I chose duplex roller chain and only use one side. Roller chain also fits my budget and won't break. If it does, it's cheap and easy to replace.

zoomkat

Quote
I would appreciate it if we could keep focus on the question at hand. It hasn't been figured out and I'm settled on the design in that aspect.
So what have you done for yourself and your project so far? No body knows what your design and building capabilities are. What kind of bearing will you use? Your best bet is to research similar bots to what you want to build, and go with motors those bots use.
Google forum search: Use Google Search box in upper right side of this page.
Why I like my 2005 Rio Yellow Honda S2000  https://www.youtube.com/watch?v=pWjMvrkUqX0

dritchie

So what have you done for yourself and your project so far? No body knows what your design and building capabilities are. What kind of bearing will you use? Your best bet is to research similar bots to what you want to build, and go with motors those bots use.
I know more about this than I what I'm willing to share. You don't even purchase a motor until you figure out the forces. I was just seeing what you people come up with; which is pretty lackluster in my opinion. You don't know so you revert back to copying other peoples work or general fixes. The only engineering experience you have is what is spoon fed to you in a pre-made kit.

keeper63

Is this guy trollin'? I sincerely hope not!

:D :D :D

I don't have any engineering experience - but I think between what you've already found (online calculators and such) - and maybe the information presented in this book (which has a section or two devoted to the mathematics needed, and how to work the problem, to answer your questions) - you should be able to get the answer you need.

BTW - if you're wedded to the dual-chain system, then so be it. I just wanted to point out another resource to you, in case you weren't aware of it (and for others, too), because building a working tread system for larger tank-style robots is a challenge. Nothing inexpensive exists on the market; what does exist will figuratively set your wallet on fire.

Good luck with your project, and I hope you find your answer.
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

MarkT

So the motors I was looking at have a max torque of 619 oz-in (or 17.5 kg) @12VDC. And that servo is 40 kg torque.

619 oz-inf is 4.35 Nm, 17.5 kg-cm is 1.7 Nm.

You need to sort out which, and I'd strongly advise using SI units throughout as its much
easier and you won't make silly mistakes.

First estimate total robot weight, then for a 45 degree slope that means your wheels have to push
with 71% of that force, so that gives a handle on the torque needed (allow a factor of 2 for
friction and drive-train losses though).

If you know how fast you want it to move up that slope that will directly give you the total
power needed (again, factor of 2), and thus you can size your motors.  Do not choose the
motor first and hope, that's just silly.   Find out the power and torque requirements (even
roughly) and then choose motor(s).  Only then choose motor drivers and battery system.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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