In the near future I will be building a CH3-R or Phoenix and I’m considering using HS-5645MG servos in lieu of HS-645MG servos to increase payload capacity. These two models appear to be completely interchangeable according to the specs and theoretically using the HS-5645MG servos would increase payload capacity by as much as 25%. Is there anyone here that has experience with these two models? Is it worth the extra money to upgrade?
Thanks,
Dustin
The difference is the 5645 is the same mechanicals as the 645 but with digital electronics to control the motor. They take the same input signal of course, however the digital electronics updates the power applied to the motor somewhere around 40x the rate of the analog electronics. This allows the digital servo to respond faster to changes in load. It also handles somewhat more load while holding a position with the same tolerance as the analog servo at the lighter load. There is also the advantage that the digital electronics will hold the last position it received if the signal were to go away while the analog electronics typically heads for an end stop of mechanical rotation. This is perhaps of more benefit when using something other than a dedicated servo controller such as the ssc-32 but I figured it was worth mentioning.
Hi,
Eddie explained very well the difference between the two popular Hitec-brothers (645 and 5645). This pop the question whether to go for analog or digital servos for a hexapod.
I’m quoting Matt Denton from his hexapodrobot forum:
Personaly I find the “digital noise” a bit annoying. The major difference is the strong holding torque for a digital servo. Unless you have incorporated terrain adaption with sensors on all legs I believe analog servos are better suited for a hexapod. Simply because the analog servos allow some joint movement when its trying to hold the position. Ex if the ground are not 100% flat, a digital servo would soon be very “stressed” because of the extra load.
One may want to check previous post on digital servos. I think one version would burn out if kept under load for any length of time.
As noted in a previous post, digital servos have a smaller deadband (slop) and better resolution. However that comes at a cost of more battery drain versus it’s analog counterpart. The buzzing noise is from the servo continually trying to hold position - even with no load.
I agree with the other comments, but one thing still needs to be addressed. The payload of the Phoenix is lower than the CH3-R due to the longer femur, but also because the joints are made up of only the servo horn. The CH3-R uses SES brackets which are much stronger mechanically because they are supported on both sides of the servo.
I knew the Phoenix’s payload is lower than the CH3-R’s because of the joint configuration. I also suspected that the Phoenix had a longer femur but I was unable to find any documentation stating as much so it’s good to have that spelled out. I would be curious to know the exact length of the femur, do you have that information?
Changing gears… I wasn’t actually trying to contrast the payload capabilities of the Phoenix and the CH3-R in my original post. My intent was to understand whether any given hexapod would be “stronger” (i.e. would have a greater overall payload) with the HS-5645MG servos in lieu of HS-645MG servos. Based on the torque ratings of the two models I’m confident the answer is yes. However the concerns highlighted by, well, pretty much everyone helped guide my ultimate decision.
Thanks,
Dustin
daemonmaker.net
The femur is 3" long.
Oops, I meant to ask about the length of the tibia. Though it’s good to know the femur is also a different length.
It’s 4"
