Pololu surplus 5475HB modding

I finally decided to grab a bunch of these while they were on special, hoping i would be able to use them to upgrade my set of HS-311’s - I have them in a robot arm, directly acting as joints , so the higher listed torque and the dual bearings on the output shaft looked great. I was hoping that it would be a simple swap, and i was hoping the biggest problem would be desoldering the 311’s motor from the PCB.

A few internal differences:

The 5475HB’s case is 1mm or so (maybe less) shorter than the 311’s. The 5475’s gears do not all mesh when mounted on the 311’s case, and the 311’s PCB does not quite fit into the 5475’s case. trimming a few mill either side of the cable entrance will enable the PCB to sit nicely enough.

The 5475HB’s motor is smaller - two sides are flat, rather than being round like the 311’s. Also the terminals are swung around 90 degrees, so they do not line up with the pads on the 311’s board. As the PCB does not fit the case perfectly, there is room to run leads to the pads on the PCB. I use stripped stranded wire, soldered one end on to the motor, then passed it through the holes in the PCB and soldered the other end. My best example so far, i left the wire untinned so thatthere wa some give to allow the PCB to be positioned best

The hole for the pot in the 5475 is round. the pot in the 311 is square. The round socket is easy enough to break apart with pliers, and the 311’s servo seems to slot nicely into place. However the position of the locating nub on the pot and the position of the stopper on the final gear means that the servo does not have full movement range if the pot is inserted, and your pot ends up being a movement limiter. I had to remove the post for the pot fastening screw to allow movement to be able to insert the pot facing the right way. Hot glue should hold it in place. I am hoping i will be able to compensate for any error in positioning via the pololu controller

SO far i have upgraded 3 of my 311’s - two of them continuous rotation.The strength of the gears in the 5475’s was apparent when i had to remove the limiter for these. Eventually i will get a serial motor controller, and use 2 of the plain surplus 5475HB’s as drive motors, replacing the current servo powered tracks (Tamiya has a cheap set of rubber tracks with drive and road wheels, axles, etc. The holes in their larger drive wheels seem to line up perfectly with the holes on the white X shaped hitec servos arms)

The upgraded servos will be going into an all new robot base - my previous bases had been balsa wood, with the drive servos at the rear. Due to the weight of the 2x 6v 12AH SLA’s it is carrying, the rubber track would stretch when in reverse, causing it to slow down and usualy lose a track. The new robot will be based, literally, on an Asus WL500G wireless router, tracked, with the drive servos mounted towards the middle of the base, and the batteries between them. I am going to use thermoplastic to create mounts for all of the assorted bits… 3 servos is enough for me to start positioning hardware on the robot. The normal servo will be wedged between the two batteries on top of the router, as the base for the rest of the arm, and the two rotating servos on either side,mounted in the middle to keep track stretch as similar as possible in either forwards or reverse.


Thank you for sharing your work with us, and I’d love to hear more about your robot as it progresses!

- Ben

A few more things i noticed…

The 311 servos i have ( 8 in total) come in 2 revisions - one has a resistor between the motor terminals, the other does not.

Also, the standard rotation servo i modded seems to respond in an odd way since i resoldered the leads from the 311’s PCB to the surplus servo’s motor. Originally i used insulated wire, this time i used sections of flat desoldering braid. The back of the 5475 motor is plastic, and there are no components on the underside of the 11’s PCB.
Now the servo only seems to respond when i send it extreme values via the pololu controller - and then the motor will continue to strain in that direction. I dont recall this happening previously, i will check the PCB to make sure i didnt bridge anything. Possibly, it can be fixed in software, but i dont think so.

I have created servo mounts out of polymorph plastic for the fully rotating drive servos, and have also created a mount for the servo that acts as a base for the robot arm, using polymorph plastic as well. The base servo is jammed between a pair of SLA batteries, all of which are held in place with polymorph plastic.

Next up - the road wheel mounts (1 axle + 2 bearings each, 3 on each side) should get it running, and then maybe a set of front and rear “air wheels” to give it the stereotypical tank-track look.

I sorted out the issue with the modded standard rotation servo - Wrong polarity on the motor. Desoldered it, turned it around, resoldered, all good now!