Hello everyone! I would like to develop a robotic mower, I saw on the internet similar projects where to print the frame, wheels or linked sites where to buy them in 3d, but they cost between 250 € and up (electronic excluded, only the body) and, in my opinion I can do with much less, only it serves a plastic box with 3 wheels.
The real question is: since the brushless motors have no special attacks, what do you think the best way or simply the proper way to attach the wheels, like these?
I hope I explained, my question is mechanical, there are some motor adapters threaded screw? I have to create a pulley? paste them? I do not know: D
Thank you.
iacoposk8:
Hello everyone! I would like to develop a robotic mower, I saw on the internet similar projects where to print the frame, wheels or linked sites where to buy them in 3d, but they cost between 250 € and up (electronic excluded, only the body) and, in my opinion I can do with much less, only it serves a plastic box with 3 wheels.
The real question is: since the brushless motors have no special attacks, what do you think the best way or simply the proper way to attach the wheels, like these?
I hope I explained, my question is mechanical, there are some motor adapters threaded screw? I have to create a pulley? paste them? I do not know: D
Well - that's part of the fun in building a robot - figuring out conundrums like these. First off, though, I am going to recommend to a couple of resources which will help you in your journey and beyond (hopefully):
Both can help you, and give you ideas.
Ok - now, on to your question. First off, note that those wheels you posted are meant for a full-sized lawnmower. They are 8" in diameter, and they aren't lightweight (given their purpose). If you were going to use these for a lawn-mowing robot, that tells me you plan on building a full-sized lawn-mower robot. So the remainder of my post will be from that angle.
Look at the image of those wheels again - notice the black plastic disk with the hole in it? Notice the pressed-in bearing on the hub of the wheel? Also, notice the inner gear surface on the wheel? What all of these tell me is one thing; these wheels were meant for a self-propelled lawn mower. Basically, the lawnmower engine (or another motor in some cases) powers the wheels indirectly via a transmission. This transmission is used to "gear-down" the output of the motor (slow it down, and increase torque). A couple of shafts extend from the transmission (or more generally, one shaft that runs the width of the mower deck is used) which have at the ends connected a pair of gears. The shaft and gears pass through the offset hole on that round black plastic disk, which is meant as a debris shield/shroud (and probably works about as well as you would expect - which means "not at all"). The gears mesh with the inner gear surface of the wheel.
The wheel itself rotates, via the bearing, on its own shaft (which also passes through the black shroud via the middle hole). The reason the wheel rotates separately on a shaft, instead of being connected directly to the output shaft of the transmission system, is two fold:
By doing so, the last stage of the gear-down system is moved to the wheels, reducing the size of the transmission.
More importantly, the weight of the mower rests on the shaft and bearings of the wheels - and not that of the transmission and/or the motor system that is driving it.
In short - when you connect your motors to your wheels, you need to be certain that there is proper support, and that the radial force on the wheel isn't transmitted back to the gearing or the motor (which will ultimately lead to premature failure of those parts).
So - you want a way to use this wheel. Well - probably the easiest way to use such a wheel would be to use a toothed-belt drive system. It will give you the similar advantage of a chain drive, but be lighter weight, and possibly less expensive. To that end, you would want to select two identical pitch cogged pulleys, and a belt to go around them. One pulley will be larger than the other; the larger one would be for the wheel, and the smaller one would be for the motor.
You would mount your wheel again on its own axle. The larger cogged pulley would be mounted concentric to the wheel and shaft - in other words, the shaft would need to pass through the cogged pulley, with a loose and ideally non-contacting manner. Bolts could be passed through the face of the pulley (perhaps with some spacers) through the wheel hub (note the convenient holes already made in the wheel - perhaps they could be used). That will secure the pulley on the wheel, while still allowing both to rotate on the shaft, and for the weight of the robot to rest on the shaft itself (the shaft, of course, is attached to the robot's frame).
The other pulley (the smaller one) would be attached to the drive motor. This motor needs to be sized to be able to move the total weight of the robot (see the first book I linked for more details on how to calculate the torque spec for the motor), after being completely geared down. You will want to use a geared motor (not a direct attachment) because you would need the torque to move the robot mower, plus you don't need the robot to be a speed demon (it's mowing a lawn, not winning a drag race). Likely a motor with an output of between 50 and 100 RPM would be adequate, but you still need the torque values.
Most builders of such full-sized lawn mower robots use wheelchair motors for this task - mainly because they are very robust, and very high-torque (they have to be, in order to move the weight of the chair, batteries, and person on-board - in other words, several hundred pounds). They also are typically designed so that the wheels attach directly to the output shaft (in which case, the support is built in to the gearbox). The downside of such motors is that they are typically 24 volt, plus they are very heavy, and they aren't cheap (unless you get lucky on craigslist).
Regardless, know that for a full-sized lawn mowing robot, you are going to need large geared motors to move the mass around. Also note that if you are building such a large robot, make sure one of the first things you design for it is a safety shutoff system - something with a big red non-reset-able safety button (along with other redundant safety systems, including automated error checking and shutdown, plus remote shutdown). You do not want one of these going out of control (even though it won't be moving very fast, because it has a spinning blade, you want a means to easily stop and shut it down just in case).
Hello, excuse the late reply.
Thank you so much, you were really exhaustive.
You can indicate a site where you can buy gears, pulleys, drive shafts etc.?
iacoposk8:
Hello, excuse the late reply.
Thank you so much, you were really exhaustive.
You can indicate a site where you can buy gears, pulleys, drive shafts etc.?
These are going to be among your best bets for most stuff - just be aware that the prices can be insane for certain things:
For most everything else, Ebay and Amazon are probably the best bet - there's a ton of stuff you can get direct or almost direct from China. You have to be savvy, though, about who to order from - remember, if the deal seems too good to be true, it probably is. Do your research, trust your gut.
Finally - unless you're planning on building stuff for sale as a business or vendor, a lot of parts and such can be scavenged from junk (or close to junk). For instance, there are great motors and gearboxes to be found in old drills picked up cheap from Goodwill. Yard sales can have interesting stuff, too. If you have a bulk-trash pickup program or other recycling program, get to know when placement occurs in your area, then go out and scavenge - you'd be surprised what people get rid of that contains a ton of fun stuff. Finally - if you have an "el-cheapo-tools" place near you (you know - the kind that imports everything from China - here in the USA, it's called "Harbor Freight") - sometimes, you can get interesting parts from their cheap crap (just buy it, and tear it apart and re-use it).
Oh - and one other place to look at (if you are in or near the USA):
They have parts and replacement components that are sometimes hard to find elsewhere.
Finally - don't discount pull-a-part auto salvage yards - plenty of useful motors and other mechanical components can be found in cars and trucks (also, be on the lookout for specialty "pull-a-part" places - there are some that specialize in only certain kinds of vehicles, which may have parts you can't find in ordinary automobiles).
