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New servos


We’re please to offer two new servos:

  1. Parallax continuous rotation servos. These are Futaba S148 servos that have been modified for continuous rotation. Since they can be directly controlled by a microcontroller without any other external electronics, these servos are an easy and inexpensive way to get your robot moving.

  1. Surplus Hitec HS-5475HB servos with the electronics removed. These servos lack their control electronics and feedback potentiometers, but each comes with standard servo housing containing a 3-pole ferrite motor and a geartrain comprised of four heavy-duty Karbonite gears and two ball bearings. The servo can be easily modified for continuous rotation and driven by a standard H-bridge or motor controller.

We have also added some new wheels and sprockets, including ones that are designed to fit on Futaba servo splines and are compatible with the Hitec HS-5475HB servo spline.

- Ben


Would you know the size on the surplus HiTec Servos? Im trying to create a Solidworks model and the problem is that either I can’t measure the hole correctly with a caliper or my model is incorrect.


Hitec’s datasheet for the HS-5475HB (here) includes a schematic. It’s pretty rough, but it includes the outer dimensions and mounting hole placements.

I really wish servo companies would put out good schematic drawings, or better yet non-proprietary format 3D cad files of their products. With all the curves, bumps, and notches it’s really time consuming to make an accurate model if you need to fit it into a tight space.


P.S. Out of curiosity, what’s your cad program of choice?


As of right now Im using Solidworks though I do have Inventor installed. I didn’t really have any particular reason for the choice besides the fact that there is robotics videos that they will be showing in may. Part of my problem is that Im an electrical engineer. I have no clue how to use a caliper. Can I use the internal jaws http://en.wikipedia.org/wiki/Caliper (See diagram) to measure the diameter of a hole or is that the wrong way?
Im measuring around .173 inches as the diameter. I think that is the right diameter though Im utterly confused as to why it appears that HiTec used bother metric and English measurements.


It sounds like you’re using them right, are you zeroing them before you start (not applicable to vernier calipers)? how accurate of a model are you trying to create? The inside jaws are good at measuring parallel surfaces and large holes, but because of the slight offset of the jaws they’re less accurate when you try to measure small holes. To find the center of a servo mounting hole I wouldn’t trust an inside jaw measurement, I would take outside jaw measurements of the overall servo width, then measurements from each side of the servo to the closest edge of the hole, and subtract these from the overall width (I hope that made sense). Or I would just go online and find a schematic.

If I needed to know the size of a small hole to great precision I would find the best fit wire-gauge drill bit (if you have a set, they step in size by a few thousandths of an inch) and go off the known size of it, or just measure it with the inside jaws. The accuracy of the inside jaws doesn’t drop with smaller measurements, as they overlap and are completely parallel. This is way overkill for anything made out of plastic.

By the way, are you using vernier or dial calipers? I lost all patience for analog measuring when I discovered you can get really decent off-brand digital readout calipers (english and metric in one tool, oh yeah!) on e-bay or from local Harbor Freight stores for under $20. Is there one near you? By really decent I mean gets within 0.001" of measurements taken with a $100+ pair of Mitutoyo digital calipers every time!

I would stay away from the plastic (“compostie”) ones, but I use these 6" calipers every day ($20, I got them on sale for $15). I like the thumb-wheel for small motions, but I have friends who love the slightly cheaper 4" model for it’s pocket-size. I’d rather have two 6" pairs, one for home and one for work!



This sums it up nicely:

Assuming they’re properly zeroed when you start. Unless you’re using vernier calipers, checking the zero reading every time you pick them up off the table is a good habit to get into.



I am not tyring to find the center of the hole just the diameter. The way I am going to check the model is just print out the drawings to scale. It worked surprisingly well the last time when I created footprints in Altium. The problem I was having was not related to measuring. I just had to stare at the servo for a awfully long time before I figured out that I was making the wrong assumptions about the hole.