Asked — Edited

Physical Servo Modifications

This goes out to the guys who build bigger robots.

I have taken standard servos and stacked them to build a "Spine" for my new project. I find the rotational servos weak in the bearing area. I plan on adding a plate with an additional ball bearing to give more strength to the shaft area. Other than buying larger heavy duty servos, has anyone else modified servos to add strength? Any ideas?

I also made a heavy duty lever which seems to remove some flex in the lever servos which helps in this area. I will build wider adapters for the back and bottom of the servo to spread the load when clipping or stacking the servos together. This may also help.

I am requesting other members ideas and opinions to be able to build a more ridged "Spine for my project, but not add a lot of weight.

I will update my project progress with pictures soon.

Ron R

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Hi Ron, I totally understand wanting to beef up a servo. Usually standard servos have a challenge with a big lateral load. I faed this problem when designing my B9 Robot arm. If you dont have your heart set on scratch building a support there is a off the shelf solution. ServoCity sells something called Servoblocks. They come in different styles and have them to fit either Hitec or Futaba standard servos. Here's a cut from the web page listing one style:

ServoBlocks increase a servo‚Äôs load-bearing capabilities by helping to isolate the lateral load from the servo spline and case. The extreme versatility of ServoBlocks allow users to create complex, extremely rigid, structures with ease using standard Hitec servos. The ½ aluminum hub shaft provides multiple mounting options using 6-32 screws. The robust 6061 T-6 aluminum framework acts as a servo 
exoskeleton, greatly enhancing the mechanical loads the servo can withstand.  

This is what they look like:

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Here you can see how I used one to support the heavy wrist and claw of my B9 arm:

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Go here to shop, choose and buy: ServoCity's ServoBlocks

Hope this helps, Dave


WOW ... Thanks Dave. I can see this idea can resolve my problem. My only concern is weight. I will look at it online for the details. This maybe a concept for a 3D printed one incorporated into my spine assembly?

I like your Buddy in the lower left corner of the picture too.

Ron R


Glad this helps Ron. I don't know much about strength of 3D printed plastic so I cant comment intelligently on that. I'm a metal guy but I do know that ABS plastic is very strong and may work. However I think you may get too much flex from plastic to rigidly support a lateral load properly. That's just a speculation though.

Yah, Skye is a fun little friend. She seem to always be there when I need a smile. I didn't even notice her in this pic till after I took it and looked at it later. :P

Good luck and have fun. Dave



This is a picture of my test layout. The lower most servo is the one we talked about. I may use the same idea on the lever servos also. This will also have a pelvis of similar design. Legs will be like the arms.

I will post a project update soon.

Ron R

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Hi Dave and Skye,

I looked at the servo City's site. A lot of good stuff which I will be ordering. What I don't see is spline shafting. Do you know any where I can get some. I was going to put out a request to the community for blown up servos (LOL) for the gears with the spline. As you see I have little space to work with and weight is a big concern. I have to finish the spine and build a pelvis and legs. This means mounting 10 more servos to operate the hips and legs. All the weight is in the servos and mechanics around them.

By the way, I can't wait to see the next video of your Big Guy's progress. It has been VERY enjoyable watching your dream come true.

Thanks for your help,

Ron R


Hi Ron,

Thanks for the very kind words. The "Big Guy" is a passion and dream coming true. Skye keeps me company a lot of the time during the long hours I spend in the shop working on him. Your concept is very cool. I cant wait to see how it progresses. I'll be watching!

I'm not sure what you mean by spline shafting. If you mean a way to extend the shaft away from the servo spline ServoCity does have many ways to do this. Look at the following links for a few of the many options they have:

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I was looking for the actual spline used on a servo. Many of the flanges and adapters I have use the i.d. spline used on the servo. I was trying to get a length of the o.d. spline to join existing flanges together etc.. If it is unavailable, I will try using the items you showed me from the web site. Thanks for the additional info. I will keep you posted as to my progress.

Ron R


The EZ Robot servos use a Futaba 3f on the standard servos. I want to find a rod about 12" long of this spline to make up the adapters. otherwise I will use the parts you showed me. I can use the spline couplings with the set screws which should do the job.

Thanks for the servo city site. I should find all my needs there.

Ron R

PS Thank


Sweet, that's what I was thinking. Glad this is helpful. Happy building!


By the way, have you ever used a servo synchronizer to connect 2 servos for more power?


@andy, I have 3 joints in my InMoov robot that have 2 servo's connected together for more power. I did it by taking the power leads from one intact servo and connecting them to the motor in the second servo. The second servo has the stop and the card disabled. ( I had some that I had fried the card on). This method works really well and if you need one servo to rotate in the opposite direction to the other, just reverse the power leads. I like robot and how you have used the EZ Bits build portions of it. Do you have a video of it moving?



I have only done basic servo movements. I just finished assembling it the other day and due to the weakness in the spine I don't want to move the arms around too much for fear of breaking stuff. I am building a load bearing plate to try supporting the upper weight thru the spine based on the ideas from Dave. I will try to get that done today or tomorrow. Once that is proven out I will try my hand at loading a video.

Ron R


Sounds good, looking forward to the video.