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The right motors for the job?

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New ( offline )
Posts: 6
Posted: 2008-01-25 01:22 
I am going to be building a 6 wheeled rover here very shortly it is going to be used for several things, one will be plowing snow, another will be surveillance.

I am going to be building it similar to the Machine Labs MMP-8 except one of the goals of mine will be that it will have to be able to go up a flight of stairs. Therefore I need to use much larger tires than they use. The tires I have in mind are 7.50" in diameter.

I know the MMP-8 uses 37mm gearhead motors, with either a 30:1 or 50:1 gear reduction. Running on 12 volts will those motors be strong enough to power the rig I have in mind, or is there something better suited for this job?


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Posts: 844
Posted: 2008-01-25 07:46 
Well hello,

Fisrt thing: how much snow do you have to push, I know where I live I can get 1 meter (more than 3 feet)... a small robot like that couldn't push it... you should see the plows we use... :lol:

Honestly, I don't think changing the diameter of the wheels will make it able to go up stairs :wink: You would have to go with something like:


I think the biggest problem you will enconter with pushing snow it that you will have almost no traction... I think I would go with tracks and pulk up the weight as much as you can (and as is useful, not TOO much)

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Posts: 6
Posted: 2008-01-25 07:54 
Changing the size of the tires does make it go up stairs much easier, simple logic says that a 7 inch tire is going to have a lot easier time climbing a 6 inch vertical face than a 3 inch tire will.

I have an 18" wheelbase 4 tired vehicle right now with 7 inch tall tires that can climb up stairs with a little work. By stretching the wheelbase on this new one to 20 inches and adding another set of tires in the middle it should do fine.


Last edited by RCCrawler on 2008-01-25 08:12, edited 1 time in total.

Expert ( offline )
Posts: 844
Posted: 2008-01-25 08:04 
RCCrawler wrote:
Changing the size of the tires does make it go up stairs much easier, simple logic says that a 7 inch tire is going to have a lot easier time climbing a 6 inch vertical face than a 3 inch tire will.

I have an 18" wheelbase vehicle right now with 7 inch tall tires that can climb up stairs with a little work. By stretching the wheelbase on this new one to 20 inches and adding another set of tires in the middle it should do fine.


Well, of course it's going to have it easier because 3 inch tire cannot bling 6 inch staires :lol:

Really? Well show us when you get it to work, make a vid. Oh, and how much snow did you want to push?

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Sam


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Posted: 2008-01-25 08:13 
Nothing to serious with the snow, maybe 6 inches.


Expert ( offline )
Posts: 984
Posted: 2008-01-25 09:25 
To push 6" of snow you will need a bot that weights at least 150lbs. There are a few videos kicking around the net of a r/c truck with a plow on a driveway pushing 1/8" of snow. And another of a 30lb 1/4 scale truck pushing an inch. To push 6" inches of snow, tracks would be better, or studded tires. And 150 lbs would be the minimum.

You should look at a 2 or 3 foot long rover at least. An 18" long rover with 7" wheels won't climb 6" tall stairs. Trust me. You simply need more length or tracks.

For motors, you will need something like this:

http://www.robotmarketplace.com/products/NPC-T74.html
Driving each side of the rover. Use a Vantec, IFI or RS80 to drive them.

Or you could buy 6 of these:
http://www.superdroidrobots.com/shop/it ... 34&catid=7

And run them off a Sabertooth 2X25's.

You'll be getting close to enough power with the small gear motors but you'll want to build heavy.

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Posts: 6
Posted: 2008-01-25 09:50 
Wow, 150lbs. I was going for something more in the 50lb range, but I understand that it takes a lot of weight to push that much snow.

Like I said I currently have an 18" wheelbase vehicle that with 7 inch tires will climb stairs with some driving skill. If I lengthened it to 19" it would go straight up them no problem. That's why I thought about extending this to 20", but maybe even a little more would be better.

Here are some other motors I found that seen like maybe a decent option, BaneBots is local to me as well, so I might take a drive up to them.

Edit: won't let me post links... Banebots website, 550 motor 48:1 reduction.

As you can tell by my screen name I am very big into Radio Controlled Rockcrawlers, this new rig is just going to be a play on that. For the most part just something to have fun with.


Expert ( offline )
Posts: 984
Posted: 2008-01-25 10:50 
I assume you mean these:
http://www.trossenrobotics.com/store/p/ ... S-550.aspx

These are great motors, used the before. They are current pigs tough. Their actual stall current is closer to 89A. The good part is you can directly swap the 550 for a 700 sized motor which will give you about a 30% power increase.

Problem is, if you have 6 of these, you need a controller that can do 270amps per side. Or realistically, 200 per side would likely cut it. http://www.robotmarketplace.com/product ... FLOW2.html
You could use an ampflow controller for 3 motor per side, but it may cut out if you stall the motors. They are rated for 160 continuous per side. 180 peak for half a minute.

Pushing snow takes some serious weight which takes some serious power.

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Posts: 633
Posted: 2008-01-25 11:19 
evolution wrote:
Pushing snow takes some serious weight which takes some serious power.

...and brings your motors considerably closer to stall, for longer periods, than would normally be encountered while driving around in mixed terrain. If you're going to be bulldozing, I'd definitely design for the stall current, rather than the running current.

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Posts: 9257
Posted: 2008-01-25 11:29 
You mentioned changing the tires from 3" to 7". Remember the torque of the motor/wheel goes down as the diameter goes up. So changing tire size may make it physically capable of clearing the steps for climbing, the power of the motor/wheel will drop dramatically. Larger wheels require more powerful motors. ;)

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Posts: 984
Posted: 2008-01-25 12:42 
Yup and 7" tires will be pushing it for the 1:48 banebot motors. You would likely have to go with the 1:64 ratio in the 42mm gearbox but that dramatically reduces your speed.

Something like what you want to do, you will likely have to make the leap into the battlebot parts. Getting into 3/8" and 1/2" shafts, chain drive, large mag or NPC motors and 160 amp per channel controllers.

You're basically building a small lawn tractor. lol Which is pretty cool. But your cost for a project like this will be $2000 and up easy. $300 per motor, $600 controller, that's $1200 there. Then you'll spend $400 in shafts, chain, sprockets and bearings. Another couple hundred for materials and an r/c controller. You would end up with a cool rover though.

If you ditch the snow plow idea, things can be alot cheaper. I'm not trying to discourage you either, just keeping it real so you know what you're looking at.

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Posted: 2008-01-25 14:00 
Just a reality check, but you won't be able to push any amount of snow with a small wheeled bot. Also a wheeled bot will have problems climbing normal stairs unless it has really large tires, maybe at least 3X the height of the stairs. Being a long multitired bot will make stair climbing even more difficult. I looked at the Machine Labs MMP-8 videos and it doesn't climb over anything of significant size.


Expert ( offline )
Posts: 984
Posted: 2008-01-25 14:47 
With enough power, weight and traction, even 6" tires can climb 6" carpeted stairs. They will literally climb up each step. The trick is having loads of power, lots of tractions and a suspension and size that will compliment climbing stairs. Designing it is key. Do a search for stair climbing videos of rovers and you'll see some of the successes and some of the failed attempts.

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Posted: 2008-01-25 15:18 
Wich will bring the price up too (the suspention). :lol:

This is going to be one bot!

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Sam


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Posts: 2446
Posted: 2008-01-25 15:23 
I would invest in some snowblower tracks for this project as I don't think tires will suffice. Anyone knows tracks have loads more traction than tires, and used snowblower tracks can easily be found on ebay for a couple hundred dollars.

Hell, while your at it why not just buy a whole snowblower and remote control that?

http://cgi.ebay.ca/Nw-Snowblower-Throwe ... dZViewItem amazing:

:roll:

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