Finally got all the mechanical problems fixed, had to add tentioners on the tracks so the tracks would stay on the sprockets. Now i’m faced with a power problem.
I built this tank to mow a very steep hill in my back yard. The tank has no problem going up and down it. Now i need to add some sort of cutting system under it. This is more power drain and weight to the robot. As it is now i only get about 15 to 20 minutes of use per battery (Even less on the large hill). Not enough time to mow the hill, would take maybe 6 or more batteries. Was looking in Botmag and seen a hybrid backyard robot. They have some plans for using an alternator and a small motor, I really like this idea but i have never built a board before. I’m they type of guy that buys serial devices to make it easy on me. There system uses a 12v battery, mine uses 14.4v for the motors, plus i want to power the basic atom and the scc-32 servo controller at 6v.
So i guess my question is how would i get my devices to work on 12v and maybe a way to get a board made cheap.
Im not too sure how to do that, (im all about mechanics ), but I can tell you if you need inspiration for building the cutting blades look at the lawnbots blades: Link
from their reviews they seem to be very good at what they do (and for that price they better! )
Also I’d use a brushless motor to propel this. Im not sure how many RMP’s you will need, but again, for a rough estimate look at other commercial mowers.
just curious, how steep is a steep hill? a similar project (for a similar situation) is down the road for me but I have not made any significant $ investment in it yet.
I have been pondering about using a weed whacker head instead of blade(s). dead weed whackers seem easy enough to come by for parts, and the odds of stalling out and burning something up on a hard obstacle are less. for power I was looking at brushless motors, probably a GBx2 or GBx3 outrunner wound for around 200W. nice thing is if you stall it nothing breaks or burns up. Outruners are nice and torquey, esp if wound LRK, so that seems like a reasonable selection criteria. I’m not sure the common 3mm shaft on a GBx will handle the stall directly though, probably wind up using a small gear reduction through a belt drive or something so the whacker head can be on its own set of bearings. just some thoughts anyway.
I don’t think string gives as uniform a cut of course but if you are moving slowly it might be acceptable. I was thinking I could rig my weed whacker onto a small wagon and push it across an area of lawn to get a feel for velocity and rpm required to get a decent cut rather than having it look like a total hack job. of course the slope I’m trying to mow has ruts and rough spots in it already from my attempts to push a mower up, down, across, in an arc, on a string, etc trying to mow it for the last 2 summers. as it is now I just let it grow and hack it down with the weed whacker every month so. it’s not like it’s gonna look any worse with a robot doing the hacking.
A lot depends on how much $$$ you have to put into the project. Also is it to be a toy type of project or expected to seriously cut grass, and how big is the area to be mowed? If it is a serious project, I’d start with an existing lawn mower, and then modify it to be remotely controlled. If the area is of any size, then it probably needs to be gas powered for cutting and locomotion. Getting a used self powered lawn mower would be a starting point. I keep eyeing my old snapper riding mower as an ROV platform.
The whole yard is a hill just one part in the back is were i will need the tracks. http://home.comcast.net/~ccook1289/hill1.JPG
The club house castle is 20 feet tall to give you idea how steep the hill is.
I want this to some day mow the whole yard on its own. I have a 14 channel gps and sd reader to plot the yard. I might need a compass also haven’t got that far yet.
Interesting power plant Hybrid
This is the system i was talking about converting. I think if i could add something like this i would have no power problems. I’m no good at building boards i’m more of a programmer. Help on building hybrid.
I think for actual serious grass cutting, I’d start with self propelled mowers like below and add the ROV materials. With clever construction, the mower could still be used for regular grass cutting, and with the ROV components removed, have some resale value. The electric start model already has a built in electrical system.
Question about converting ac to dc.
If i were to buy a this cheap generator northerntool.com/webapp/wcs/stores/servlet/product_6970_200313480_200313480
it puts out 120 v with 1000 watts to convert to amps (Amps = Watts/Volts)
1000 watts/ 120 v = 8.3 amps
how would i convert that to dc
if i convert the volts to 13.8 it gives me 72.4 amps but i’m lost the the ac to dc convertion. 72 amps would be great but don’t believe i did that right.
Not only that, but were getting into the problem of size and weight when you add all of this equipment. Realistically this could become as large as a ride-on if your not careful. I think something low-ground and wide would suit this feild of work so that it is not to tip, flip or wobble on the un-even and wonky terrain.
What you are talking about (ref: Ac to DC conversion) is a DC Power supply, the same type of power supply you would plug into a wall outlet at home. In the 1KW range these are not small things, however, unless you are looking to use all 1KW of output from the generator there is nothing preventing you from just using the size power supply you need. So if you need 20A at 13.8V then go buy a 20-25A power supply and run it off your generator. Alternately if you peak load is say 35A but most of the time it’s less than say 20A you can use a small garden tractor battery as a buffer, using a 20A power supply to float charge the battery and handle most of the nominal load while allowing the battery to handle the peak loads. Anyway, we use a lot of Astron supplies at work, several 20A and 35A ones and a few 50A ones. We actually have an 80A peak load product wired up as I described with a battery and 50A supply on a fixture. The stuff is expensive brand new although sometimes you can pick them up reasonably cheap on ebay (but you need to be careful about ones having been “repaired”).
I’m building something on a similar size scale as you (3 sets of 3" tracks per side). I also plan on using a chain drive (probably a two-stage chain reduction) since I need to gear my motors down somewhere between 1:9 and 1:11. I was wondering if you could provide any additional info on how you’re attaching your drive sprockets to the lynxmotion hubs. I know you said you made some custom axles, but I can’t find sprockets anywhere with a bore less than 1/4" (this would be easy if I could find sprockets with a 6mm bore, but no luck).
I am using 1/4" stuff with everything I do… 6mm is only like .013" or something away from 1/4… so I figure thats in the noise.
I will be driving my 3" tracks with a roller chain sprocket with a 7/8" bore, attached to Jim’s 3" idlers. It should nestle between the injection molded track sprockets quite well. That in turn is connected via #25 roller chain to a 1/4" axle (via another sprocket of course), and then to my 6mm shafted motor (PGHM-02) via what mcmaster calls a “spider” coupling. (at least thats the current plan)
Well, the smallest bore sprocket that I can find is 1/4" which is 6.35mm, so if I drill anything out it would have to be the lynxmotion hubs. How difficult would this be to make sure I drill it out properly with a dremel (I don’t own a drill press). I’m assuming that to prevent wobble this needs to be perfectly centered (I’m shooting for between 200-350 rpm depending on how I decide to gear it).
The 3" idlers (HUB-13) have an outer diameter of 0.865". The roller sprockets I am looking at have a bore of 0.875", and come with a keyway and set screw.
I plan to place the roller chain sprocket over the large part of the idler (i.e., the center), and ‘sandwich’ it between the two LM Track Sprockets.
At first I will try just the set screw, see how well that holds up. If I need to, I will find some way to add a keyway to the idler.
), but I can tell you if you need inspiration for building the cutting blades look at the lawnbots blades: 
)
