should i get 8x HS-645MG for all 8 servos on the leg? or i should get something else?
edit: Also i could get 8 HS-5685MH servocity has them for $40 each.
I know on the picture they have the robot with the 5645 but they are the same price as the 5685… Just not sure if they are good enough to hold all the weight
Also the 5685 are 7.4V compared with the 5645 which are 6V
I think the new owners are all off today for Canadian Thanksgiving!
The only Biped (disregarding Robonova) was a brat, I went with 645s, but if I were to go any larger I would probably go with digital… Not sure which one, as don’t know if hitec changed the sizes of them at all, which can cause problems with brackets fitting… I have not used many of their digital servos as they are noisy!
I think perhaps Kurt meant the Scout which suggests a choice of servos. lynxmotion.com/c-85-bipeds.aspx. Lynxmotion also offers a BRAT which comes with 422 servos standard but offers two servo upgrade options. I have an earlier BBII BRAT and the 422 servos are very limited as you fear.
You have me confused about what you intend to build as you start by citing two different projects: the Ironman and the Astro. Their pictures show 21 servos in Ironman and 22 or possibly 23 servos in Astro. The 23rd servo, if there, has its axis running front to back where the upper torso connects to the C bracket from the lower torso. Your listings show 6 leg servos at one point for a total of 19 servos and 8 leg servos elsewhere for a total of 21. So you may want to recompute costs.
Good luck. Either project looks fascinating. We would like to see videos of your build and your opinions of the pros and cons of the project, especially a mention of any alterations you make.
Ya i just realized that they are 2 different robots
I place an order this morning but i based my self on the irnman4… Even though know that i look at the wastro looks betters but i never saw the torso part, and i just saw that it says it is a prototype… So anyways Here is what i ordered:
16 x Hitec HS-5645MG
4 x Hitec HS-5645MG (hands)
1 x BT-01
6 x ASB-04
5 x ASB-09
1 x ARF-01
2 x RH-01
2 x NSRF-01 (for fast proto)
2 x ASB-11
1 x SSC-32 (with sequencer software)
1 x Bat-05 (hoefully is good enough)
Hi Ted, you are correct, you can have lower cost servos with the brat. Looking at the first one I built (and my only one currently), it has 475s in it… I did have a second brat, which was a MechBrat and it used to have 645s, which allowed it to carry more weight… However it got disassembled and most of it’s parts now live in one of my Hex robots…
I am not an expert, but my guess would be that a hexapod is the smallest number of legs that can always keep a stable platform of at least three legs on the ground while lifting and moving the other legs. This allows a smooth walking gait without the need for shifting the Center Of Gravity to keep it above the ground contact legs. Both the biped and the quaruped require some sort of constant COG shifting to avoid toppling over. In your biped this is the purpose of the ankle servos which keep the COG over the foot plate which is in current ground contact. In a quad there is no real plate in contact but instead a constantly changing “tripod” formed by the three “down” legs.
The bipeds and quads are cheaper and easier to build, but their weight shift is more difficult to program.
I know this is a late post but the 5645’s should be plenty for walking, I’ll find out soon enough. Only when the joint angles move outside the center point does the servo undergo real strain. Not sure what the right terminology for this would be? I’m building a biped Pete type bot right now and I have 5645’s on the joints that have the largest loads, the ones with most weight per joint. The ankle, hip and knees have some of the heaviest loads at certain angles. My biped is currently able to stand with no power to the servos without collapsing at all unlike the BRAT. The BRAT’s hip servos were always under load and as soon as the power turned off, back it went.
The biped Pete style bot has more deg’s of freedom on the legs so the weight can be shifted more directly over the feet instead of leaning from side to side like a brat. I still need to add the battery, finish the arms, and add the electronics so after all is mounted up, I might realize a significant weight gain from its current state.
Here is a photo. I might change the arm config to use custom made hands that I am working on:
