Author Topic: Increasing Servo Torque  (Read 5573 times)

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Offline rabi_tagoreTopic starter

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Increasing Servo Torque
« on: March 05, 2007, 09:29:46 PM »
Hey,
I am confused about the concept of adding gears to increase the torque of a motor(or in my case, a servo). I have absolutely no problem with the theory(not that I have a strong grasp...but I can always learn it..not the tough part). But actually incorporating gears onto a servo mechanically seems confusing. U can mount a servo to a robot base by using screws and pre-made servo mounts, but how do u add gears to a servo? Won't the gears fall off without a properly defined structure made particularly to hold those gears(i probably sound extremely stupid)? Or could I simply add pre-made "torque-raisers" to my servos(if so, can u please guide me to where I can buy them or what they are called).

So basically any help regarding the constructional(not theoretical) aspect of adding gears to servos will be greatly appreciated. Any thing pre-made is preferred!...lol(dont want things to get too complicated).

Thanks a lot guys....

SOMEONE PLEASE HELP...STILL AWAITING A REPLY
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rabi_tagore.
« Last Edit: March 07, 2007, 06:11:53 PM by rabi_tagore »

Offline silent tone

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Re: Increasing Servo Torque
« Reply #1 on: March 05, 2007, 10:25:56 PM »
I've been on a quest for this myself.  Most hobby servos are too fast and too weak for my application, so I've been looking for ways to gear them down.  I haven't found a great/easy/cheap method, so I'd like some input as well. 

What I have found is that, yes you do need to mount them securely to your servo or frame.  Planetary gears are efficient and usually have high gear ratios (I'd love to get one of these in a gearbox to bolt onto a servo).  Spur gears are decently efficient and easier/cheaper than planetary gears.  I've also found that every interface between the teeth of one gear and another cuts the efficiency.  Since hobby servos already have 5-6 gears in them already, I've been looking for a way to remove all of those and replace them with a few high ratio spur gears, to gain efficiency and a higher gear ratio.  This has been a big dead-end so far.  Even finding the parts at a not-obscene price has been difficult.  I have found an off-the-shelf solution:

http://www.servocity.com/html/servo_power_gearboxes.html

The structure is pretty simple.  If you're handy, you could construct the frame they built and just relocate the pot to the axle that the output gear is on so that you keep the full range of motion.  I have seen several people warn to avoid building gearboxes if you can since they need to be rigid and precise, so I'm hesitant to attempt something complicated.

Offline Brandon121233

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Re: Increasing Servo Torque
« Reply #2 on: March 06, 2007, 06:39:55 PM »
What kind of tools do you guys have acess too, cause if you dont have a lathe and milling machine, you can pretty much rule out building the gearbox your self. And also most gear boxes that are out there are meant to decrease speed in more than a 10:1 ratio, so your servos will be going very very slowly (mabey 1 or 2 RPM), I think that they do sell slow servos. Also is it just that you need the torque increased, or you just want it slower, cause you can just buy a regular speed super high torque winch servo and have it not going full speed.
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Offline rabi_tagoreTopic starter

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Re: Increasing Servo Torque
« Reply #3 on: March 06, 2007, 06:44:13 PM »
That link certainly gave me some idea of how gearboxes are and all that and definitely gave me a new direction, but those things are sh*t expensive man...lol. Was looking for something much cheaper. Yes, ur right...making gearboxes by ourselves would require very precise structures that a common hobby person would not be able to do with a basic jigsaw or some other tool. The only option left is premade gearboxes. I will look into a bit more, but anyone else that already knows about good options for these problems, PLEASE reply.

Offline rabi_tagoreTopic starter

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Re: Increasing Servo Torque
« Reply #4 on: March 06, 2007, 06:47:41 PM »
What kind of tools do you guys have acess too, cause if you dont have a lathe and milling machine, you can pretty much rule out building the gearbox your self. And also most gear boxes that are out there are meant to decrease speed in more than a 10:1 ratio, so your servos will be going very very slowly (mabey 1 or 2 RPM), I think that they do sell slow servos. Also is it just that you need the torque increased, or you just want it slower, cause you can just buy a regular speed super high torque winch servo and have it not going full speed.

I basically want an increased torque preferably with a decreased speed...anything in that direction. I am looking for premade gearboxes itself, and since I am not looking for a specific ratio, any sort of a gearbox should work for me. But where do u get them? How do they look? How do u install them? Please do give us some direction to start some research on.
« Last Edit: March 06, 2007, 06:49:23 PM by rabi_tagore »

Offline Brandon121233

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Re: Increasing Servo Torque
« Reply #5 on: April 08, 2007, 08:00:28 PM »
It would really help me to help you I you could tell me what kind of torque and speed values you were looking for, I understand if you want to do this for your self as a learning experience, but trust me when I say it would save you tons of time and energy to find a very slow servo with very high torque, than to try and build/adapt your own.
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Offline PrinceOfFlame

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Re: Increasing Servo Torque
« Reply #6 on: April 16, 2007, 05:20:43 PM »
That is true, Brandon121233, about the tools,if you want your gearboxes to look professional, and function absolutely perfect. However, if you don't mind taking about 1-2 hours, and having your gearbox look VERY homemade,(clear plastic box with random holes and gobs of hot glue) you can make simple gearboxes from old cd cases, a dremel with a cut-off wheel, hot glue,(not as permanent as epoxy, in case you screw up)and some extra gears that you have. Yes, the plastic is pretty brittle, but so long as you don't place a heavy load on the case itself, it will hold up fairly well.

   Step one: draw out your gears and their positions in your gearbox on paper in full scale(i traced the round edges on paper with the gears already meshed). Take care to use a thin pencil and mark the location of the axles. Also make sure you decide on where you want the motor gear to mesh with its mate, and mark its location on the rear plate(described later)
   Step two: transfer the location of the axles onto desired material(metal,lexan,cd case,etc)
   Step three: put all the gears together as they would be inside the gearbox, and double check the location of your axle marks.
   Step four: drill holes so that the axles fit snugly within them. If they are loose, a small dab of hot glue will hold them.
   Step five: place gears on axles to make sure you drilled in the right position
   Step six: mark a rectangle outline around the gears(with them on the axles like step 5) giving about an extra 1/4" of room around the outside for margin of error, and then remove all the axles and gears.
   Step seven: place gears/axles under something to cover them from flying plastic bits, and then cut out your rectangle. The plastic on old cd cases more melts than cuts, so watch out...
   Step eight: determine how deep, long, and wide your gearbox needs to be to safely accomodate all the gears and axles, and ten cut two sides, an identical face plate with the same axle holes drilled, and top and bottom plates.
   Step nine: glue it all together, but leave the rear face plate off, so that you can place the gears and axles inside. After you have a box shape, place the gears and axles inside, test rotate everything to make sure it is all aligned correctly, then place the rear face plate on, slightly sunken in, and glue it around its perimeter to hold it in place. If hot glue doesn't satisfy you, use epoxy or some other more stable method(thicker materials and screws would be perfect)
   Step ten: place motor axle with gear inside designated hole(you should have done this when cutting additional rear plate during step eight)
Mount gearbox on your servo, or wherever you need it, and watch the fruits of your labor rotate maniacally before you...
I'll be making an instructable of this soon, and i'll post when i have it completed...
Hope this helps!
« Last Edit: April 17, 2007, 07:23:08 PM by PrinceOfFlame »
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