I'm wanting to create a hexapod based robot out of PVC, maybe about 3 foot tall. I'm not wanting to make it have to carry anything heavier than let's say 20lbs.
I'm still learning about some hardware in the actuators department, and know a lot of science, but not a lot of physics formulas. I'm considering trying to control each leg's from raise up to move forward by a solenoid, but need to know if I want to use a bi-directional solenoit, stepper motor, or something else to have the legs move forward and back when raised.
Price is my biggest challenge currently, even if it means a little more work. If the robot's base weighs about (8lbs maybe?), and round my total load up to 30lbs, and move 3 legs at a time, that means each leg would need to handle 10 lbs, right? Aside from that, what would be best for moving the lifted legs (PVC) in terms of price?
A lot of people new to walking robot want to start with something big, and I think it’s a really bad idea. You see, not only you have to use much stronger materials that are more expensive and harder to machine, not only you need ridiculously expensive strong actuators and a battery that is able to provide enough current, not only you have to account for inertia in everything, but it’s also very hard to test stuff, and any accident is likely to be devastating to the robot and potentially dangerous for you.
Start with something that fits on your desk. Something that you can drop to the floor without any harm, to it or the floor. Something that will not cut off your finger or electrocute you. Finally, something that will let you gain experience and feel for what to be careful about when designing the larger versions. And of course, something that won’t make you go bankrupt.
Don’t worry about the big robot for now, you will get there. Make a 1/10 scale model of it first. It won’t take much time, won’t cost much, and will improve the final project greatly.
Is there a reason you’re assuming I haven’t made a smaller one? Because I have, but not everyone puts all their creations online… (including my cosplay gadgets). Just please keep that in mind to ask next time? It feels kind of like you’re talking down, otherwise.
In other words, it isn’t good to assume someone a noob because they don’t know all what you know. It’s even worse to respond to the question they asked, but not offer a lead on it because you think they’re fluff. It’s more than fair to warn people it’s dangerous, but it’s another thing to say they’re dumb enough to cut off their finger.
Other than that, thanks for the feedback. I do have a specific reason I’m doing this project, and part of that reason is because it’s a stepping stone to being more experienced with larger hardware for making a quadraped. I keep reminding myself of the battery, and am not sticking myself to one idea or another until I know what exactly I’m using for hardware.
If that seemed like it ran on too much, that’s how it feels when people answer your question without answering. Just because I’m not a physics expect doesn’t mean I’m not good at electronics or mechanics… I just need to know what I need where I don’t know specs for larger hardware (I’ve mostly used servos and DC motors, no other actuators really).
Can you now please point me in the right direction? Most directly, what form will be most price effecient for doing the job? Thanks. :)
Sigh. I was giving genuine advice, and I didn’t mean to talk you down. This is not a question-answering machine, where you input a problem and get a ready solution in return. It’s a community of hobbyists who talk about each other’s projects and help each other as much as possible. I assumed that you are not a “noob” and don’t need a lesson in how to communicate online, but from your answer I see that’s not true, and I will try to be as patient as possible with you.
As for “being dumb enough to cut off their finger”, you really don’t have to be dumb to do that. It happens all the time, and it happens to experienced people. Especially when you assume that you are experienced and don’t need basic safety precautions. Smaller robots are just inherently safer and easier to work with, and that’s why I recommended to start there. I also don’t think it’s my responsibility to ask you for additional information about yourself or your project. If you want to be treated like an experienced builder, then behave like one.
But back to your question. Since you just want a direct answer, here it is, although I doubt it is what you are looking for, and I think that talking about your project some more would actually help you more. But since you just want an answer…
"The most cost-effective actuator for your robot is no actuator at all. Build something like the Strandbeest (http://www.strandbeest.com/) and that’s it. No actuators are actually required."
Here. If that doesn’t fit your project, maybe you would explain a little more about what it is for, what it is supposed to do exactly and how are the legs going to be configured. Start with stating the number of degrees of freedom per leg.
At 10 pounds per leg and 3 feet, the torque need to barely budge is 30 ft lbs, that’s 415 kg cm or about 30 newton meters.
That takes you up to something like a wheel chair motor. Here is a pair rated at 17 NM, you would need to gear it down 2 to1 to get 34 NM which would move the spider:
You can find used wheel chair motors for about half that price.
So, 8 of those might run $800 or so and at 27 pounds each your spider would be carrying 216 pounds of motors, each leg carrying 54 pounds. No problem just use a belt drive and gear it down some more to 10 to 1 and the motor now rotates once every 5 seconds.
You would need some custom hardware to go with all that as you will in effect, need to make servos out of that and you will need some pretty stocky H bridges to drive it. Maybe $600 for the H Bridges if you get lucky.
So, for about 2 grand US with some clever and judiscious shopping you could have a 3’ tall spider that might work very slowly, but probably wouldn’t.
I see where you’re doing with the experience part, I did take shop, but don’t see it being as much of a threat when I’m working with PVCs over metal. I guess my train of thought was “they must think I’m dumb as a brick if I can cut off my finger on PVC pipe”. Thanks for being patient. XD
For what it’s supposed to do, I’m kind of on a DNR for a group on specifics, but it needs to be able to carry maybe 20lbs (I’m considering the load might only take 10-ish on flat surfaces. It will need to be able to follow, on flat terrain and step up curbs, which is why I was looking at a poston/actuator to lift the leg.
I still don’t know what the machine is supposed to carry, but it seems to me that the strandbeest or similar approach is the best one. Then you only need one or two motors for propelling the thing forward, and not for carrying its own weight.
