Society of Robots - Robot Forum
Mechanics and Construction => Mechanics and Construction => Topic started by: Charizard on December 07, 2008, 02:10:40 AM
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Hey, guys. If i buy a servo from a supplier, usually what does it contain? Just the servo only? Or including its mount as well? Because i plan to attach the servo on an aluminium plate instead of using double tape. Any idea? Cause i check the supplier's list, they do not have servo mount. What other replacement i can use instead? Bracket maybe? But i need one servo attach horizontally and another servo attach vertically. Any advise? Thanks
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doesnt come with a mount , you have to buy a mount separately.
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Or build a mount out of plastic/metal/wood.
Just be sure to leave clearance for your wheels.
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Let say i manage to make a U shape like cage, but how can i make sure the motor won't go in and out? Because i plan to use brackets. But how to make sure it is stick at one position? Any idea other than glu? Or I have to make myself an aluminium mount that has the motor's shape to fit on it.
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Almost every servo I've seen has 2 or 4 "holes" for mounting screws.
Buy the servo, then build the bracket to work with it.
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But are the position of those holes same for all servo? Or means i only will know after i got the motor? Cause from the supplier site i get, they don't show any holes..
http://my.farnell.com/jsp/level5/module.jsp?moduleId=en/220487.xml
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Good thing you posted that link up. It is labeled as a servo, but looks like a DC motor. To use that, you would need to make/buy a bracket or holder. Don't buy that if you intend to use a hobby servo. http://www.pololu.com/search/compare/23 (http://www.pololu.com/search/compare/23) has a pretty good selection at decent prices.
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Thats not a hobby servo, it's a different kind of servo (if your'e using it with the $50 tutorial, it wont work).
You can use a commercial motor mount for them, If you look on the end of the can (motor case) there are three holes and there's a diagram next to the photo, this is how you mount it.
Essentially you need to cut a sheet of thin metal so that after bending you can form a right angle with a couple of wings that fold back to make a kind of half box (think shoe box cut diagonally from top left to bottom right to give 1 vertical square face, two triangular vertical faces and 1 horizontal square face).
If you're going to use this as a drive motor, you'll also need a gearbox. It's easier to just use a standard hobby servo modified for continous rotation.
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXDEL5&P=ML
http://www.societyofrobots.com/actuators_modifyservo.shtml
Jim
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Do you mean behind that motor there are 3 holes used for motor mount? The mount that you mean is it as drawn in A in attachment?
I found other servos from my country's supplier, but it costs about MYR 1000+ for few m Nm, but the servo that i currently choosen is just cost me few hundred MYR, any idea on what are their diff? Basically the requirement of my motor is i need about 5Nm torque.
Actually I plan to use this motor to rotate an arm which need about 5~10 Nm. If the gearbox that I choose has 20:1 ratio, is it actually can have torque of 100Nm? (based on the motor i choose, is 5Nm). Furthermore, based on the picture at the link on the gearbox choosen, are those screw use to mount my arm? Or it is used to connect my servo?
http://malaysia.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0719035
I've drawn out the system in B in the attachment, do you think that it will work? Maybe I will put a ball bearing at the pivot there. Or should i use shaft?
I am sorry that I can't use the servos that you all recomended because I only can get from manufacturers at my country. :-\
Sorry for poping out so many question, because I never use them before and I can't complete my design if I can't get it clear. Million of thanks for the help.
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The motor mount i described is as you have drawn in figure A, this would normally attach to the front of the motor (the side with the output shaft). There are mounting dimensions drawn next to the picture of the motor on your link. The differences in the servo motor's you're looking at could be wether they are brushed or brushless, 2,4or6 pole motors also differ in price.
As for the gearbox, in the past i have chosen the output speed as my primary concern as in most cases this is more important. I feel 150rpm output may be too fast for a robot arm (based on motor and gearboxes you provided) but trust me on this I DONT KNOW. Yes you would effectively get 100nM output torque (Although you should note the start up torque of the motor too.)
The screws in the picture are used to mount the gearbox to the motor. If the mount you build isn't too thick you could probably pass the screws through the mount, then gearbox to the motor. You may need to buy longer screws?
The drawing labelled B : I can't actually comment on your design as i have never built a robot arm before and don't know the final design criteria of your arm.
Just to point out that i think if positioning the arm is more important than speed then i would use the DC SERVO MOTOR with a higher ratio gearbox and an optical encoder for postion feedback. If you just want to move the arm then i would use a HOBBY SERVO http://www.tpracing.com.my/main.htm . There are some hobby servos here about halfway down the page. I believe this to be a Malaysian site but don't actually know as it's just a google hit.
For positioning dc servos are about as good as it gets (stepper's are better) and in the main are like normal dc shunt motor's.
Just make sure you collect as much data about the motor as you can before purchasing because different dc servo motor type's have different characteristics and occasionally different implemention requirements. Positioning the arm with a dc servo will definitely require an encoder, positioning a hobby servo doesn't necessarily require an encoder as rough positioning can be done in software.
P.S. when looking on the internet for hobby servos try searching for 'Radio control servo' or 'Model servo'.
Jeez I been rambling, sorry
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Nah, that is a great help =) Basically i got the general idea already. But are those motors in the tutorial are radio servo? It has feedback right? Because I just want my motor to turn from 0 to 180 degree max. I think I am gonna get the servo from the site you got. Is any miniature gearbox can work right?
Ok, there is another problem I encounter during designing. I need to use a motor to rotate a plate horizontally. Initially I just attach the motor below the pivot, but I have been told that it is not encourage to put load on the motor. So, maybe I can use a belt to drive that pivot. My major concern is:
1) How to make the pivot rotate while the stand is fix? I also want them to be sticked together because I don't want to carry two components.
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I'm using a lazy susan for a similar part in my robot NINA - for "torso" twisting.
Just mount the bottom part of the lazy susan on your robot and put the motor just underneath it. This way, the weight goes on the lazy susan and the body of the robot, not the motor. Run the motor shaft through the center of the lazy susan and you have a nice pivot mechanism.
Does this help?
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wow. That was an interesting idea!!! It not only can carry the weight, but has better balance compare to rotate it with a shaft. Thanks. So, the top of the bearing will be my weight, legs are attached around the bearing and the motor is mounted at the center of the bearing. Maybe I am not good in searching for supplier. I couldn't find a site where sell lazy susan bearing.
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I think the bearings you are looking for are 'Spherical Roller Thrust Bearings'
http://www.skf.com/portal/skf/home/products?maincatalogue=1&newlink=1_11_1&lang=en
You're losing me. I'm not entirely sure what you want here.
Do you want the joint or the motor to rotate 180 degrees?
Size is a concern also, how big is this joint going to be?
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SOrry for the late reply guys, had my exam lately. So, could hardly online. My target is to rotate my system in 360 degree. So, my idea is to put a thrust bearing below my system. Then, a servo is attached to the load thru the hole of the thrust bearing to rotate my system. I inculde thrust bearing so that all weight is supported by the bearing.
Hope you get my idea. Since I don't know thrust bearing very well, so a question comes out from my mind. How can I attach the thrust bearing to my system, is there any hole at the thrust bearing so that i can screw it to my system and stand (which is called leg in my diagram)? Because I want the trust bearing stick to my system and the stand so that I don't need to move them separately when carry my them (I don't need to move my upper system and the stand separately).
I may not explain well, feel free to confirm with me again if you have doubt.
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I Always velcro everything =D
Joe
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you mean like those stick pad on some school bag? I was thinking, will aply super glu at the thread bearing sufficient? :P