Motor/Power/ Drive recomendation?

[minotaur]

Gang,

Can any of you get me a recomendation on the following. Thanks!

1) Need to build a small wheeled platform that traverses 95% of  flat indoor floorings. ( I presume this leaves out tracked vehicles.)
2) It needs to carry about 2.5 -3 lbs including its own weight.
3) I will visually be able to drive it remotely.
4) I plan to use a lead acid rechargable batt because I am guessing I will need a 2Ah battery (heavy..)

A) Is 4 wheel drive recomended?
B) DC motor, stepper motor, or servo?
C) Speed is not critical but what torque/ power would you guess is needed?

Thanks to all the experts here to set some initial criteria for my testing!

[trigger]

http://www.societyofrobots.com/robot_tutorial.shtml

[Somchaya]

A) You don't really need a 4 wheel drive. I'd recommend using a differential drive, since it's a lot easier to construct.

B) All 3 kinds would work actually, although a DC motor might be too fast (unless it's a geared motor or you gear it down) to control remotely properly.

C) Hmm.. I'm not very good with torque calculations.

So, I recently built a differential drive robot with a single castor, that carries around 3 lbs of weight. I used 2 standard servos originally, and the speed for that was ok, although torque was kind of low. However, I used really big wheels which reduces the torque. So, for a robot carrying 2.5 - 3 lbs, those standard servos should work fine, especially if you get decent sized wheels unlike me

If you're intending to drive it remotely, it's probably better to go for a lower speed, unless you're really good with remote control cars Personally, I'm terrible at that so I have trouble controlling my robot even though it's not going very fast.

[minotaur]

Trigger, not sure what you wanted me to see in the link, most of that information is pretty basic, so let me know if I missed something.

Somchaya,

Good info, this is helpful. What standard servos did you use? I agree on the difficulty driving remotely, especially since I have quite a bit of transport delay/ lag. Hitting a wall is bad, hitting a wall fast and far away is even worse...

[Somchaya]

I used the Hitec HS-425BB (http://www.servocity.com/html/hs-425bb_super_sport_bb.html). It has a torque of 57 oz/in at 6V and can go at 62.5 rpm.

I ultimately upgraded the servos to higher-torque ones, but if you don't use huge wheels I think it should be sufficient 

[sotu]

A 2 wheeled robot is cool and got nice turnings but not to stable.

[Somchaya]

Well, a 2-wheeled robot with a caster wheel is pretty stable, as long as you don't keep the weight balanced left/right. Well, I suppose if you turn really quickly there's a higher chance of falling, but usually that's not an issue

Diff drive robots are a lot easier to construct than their 4-wheel counterparts, esp if you want to use ackerman (i.e. car) steering methods..

[sotu]

I got a 7 wheeled robot..

[Somchaya]

I got a 7 wheeled robot..

Good for you A 2-wheeled diff drive robot is still easier to build for someone who isn't very mechanically-inclined though..

[jshalcott]

If i was going to use the differental steering, but still have four wheels. Since my dc motor is not geared could i hook it up to a gear and also still a sprocket with a chain to the front wheel. my motor is an 18 volt

[sotu]

Yeah, but offcourse not all of the 7 wheels are drift wheels. There are swinging wheels and support wheels to

[Somchaya]

If i was going to use the differental steering, but still have four wheels. Since my dc motor is not geared could i hook it up to a gear and also still a sprocket with a chain to the front wheel. my motor is an 18 volt

Yeah that should be possible. I'm not exactly sure what you mean by "hook it up to a gear and also still a sprocket with a chain to the front wheel" though, but linking the two wheels on each side together with gears or chains is definitely possible.

http://www.lynxmotion.com/Category.aspx?CategoryID=30 has some 4 wheel drive differential robots. You can have a look at how they put it together and maybe that's what you had in mind?

[ed1380]

I think he mean using a jackshaft. a gear on one side and a sprocket on the other

[sotu]

Im planning on making a 2 wheeled robot (with support wheel)! it seems so easy just adding power to 1 of the wheel and not to the other for turning..!

[Somchaya]

Im planning on making a 2 wheeled robot (with support wheel)! it seems so easy just adding power to 1 of the wheel and not to the other for turning..!

Yep, diff drive robots are very easy in that regard.. However, after working with them a little, I realized it's a little troublesome when you want them to turn at a particular turn radius.. since you have to work with relative wheel speeds. A robot with ackerman steering would be easier in that way I think, since you can have separate inputs for robot speed, and robot turn angle..

Still, diff drive robots are much easier to work with in general I think..

[sotu]

On the robot i'm making now i have a turning mechanism where a little round toothed wheel is connected to a plastic board with to wheels in each end. When i add power the toothed wheel turn to one side and drift the wheel with it so it turns. But ti cant do very sudden turns.

[ed1380]

I believe it's called rack and pinion. standard on most cars now. except on cars they have a hydraulic pump helping you

[TravelingPencil]

extreme positive camber makes for a robot frame that can carry alot of weight. pair it with a good gearmotor and it supports and drives heavy loads(asuming u use strong enough materials)