key requirements for Servos for walker robots? What can I sacrifice?
June 17, 2011
I am in the midst of building a six leg walker bot. I am following a set of designs I found posted on here. Initially, it will be a 2 DOF setup, but the plan is to use it as a test bed, and expand out to 3DOF, add sensors, add increasing complex algorithms etc.
I would like to keep the costs as low as I can initially, but the flip side is that I don't want to cost cut to the point of introducing significant issues into the build, which then takes a lot of additional coding to manage.
The thing I am reseaching at the moment is servo selection for the legs. I was wondering if I could ask your advice?
In order to keep costs down, it would be good to purchase lower cost servos. However, these come with some issues:
1) Possibly higher current draw - some super cheap servos look like they are pulling 1amp in normal operation
2) Slow movement - 0.23ms makes for a cheap servo, but a slow one. I'm not sure whether this will fit in the with concept of a walker - maybe it'll end up more of a geriatric?
3) reduced load capacity - for example cheaper servos seem to sit around the 3kg/cm range, where as higher cost sit aroun the 6kg/cm range.
4) wider dead ranges
Like anything to do with an engineering project, it's all going to be about comprimise. I was wondering which of the above I can get away with, and which will lead to major issues with my build?
Are there commonly used servo models used in walkers?
Some model specifics:
Model size - approx 600mm long x 450mm wide
Weight - as yet unknown until built - which is a bit of an issue in terms of this question.
In terms of construction, I will be using 4mm carbon/ply/carbon composite for all structural components in order to give good stiffness at a low weight. Lets me have the structural strength better than Aluminium at less than 1/2 the weight. Batteries will initially be 4.3mA/H Ni-Mh's weighting about 400g, but if I need to I can shift to LiPo to bring down weight, but that means canabalising my planes.
The servos will all be based in the body itself, not on the legs - so maybe that means I can play with mechanical advantage, and get away with a reduced Kg/cm rating?
My thinking at the moment for the walker is that, in terms of priority, it gos something like:
1) As small a dead zone as possible
2) current draw
Am I on the right lines?