Let's Make Robots!

Why is your robots motors not strong enough? (Gearing)


Have you ever made a robot that ran fine when you held it, but when you put it on the floor it moved really slow (or not al all)?

Hmm… Did you use a motor without a gear? Well, there is your answer.

This may make sense to many, if so you should find something interesting. But if you never had the “aha” experience, here’s some help:

 

I often see people making their first robot and think "Hey, motors - I do not need to buy those special ones, I have some right here", and some how the thing does not work!

Do you have a driver’s license? Tried manual (some people from the US may not have tried this)? Well, if so try to start your car in 5th gear. It will not move! Ever tried starting a bicycle in the highest gear? Not very easy is it?

The RPM of the little motors you can find are high. Very high.

Even my Wall Racers are geared down, my guess is 50:1 and they are still fast (even with small wheels which are acting as down-gearing as well). If the gearing was not there, they would not be able to start: High speed = low power, low speed = high power.

You need a gearing that can both supply enough power for your robot to start up, but not so heavy (slow) that you fall asleep before it has moved an inch :)

So you need motors with a gear attached, or you need a lot of cogwheels (or a BIG one and a SMALL one, very big & very small) or a worm-gear.

I have seen one robot without gearing. It was FAST, and the wheels was SMALL (this helped, if not, it would not work), it was able to skid (motor could get the robot under control). It was light and I also think it had way too much power:

http://letsmakerobots.com/node/272

And then there is of course the solar-powered little things, where there is no wheel, just some plastic around the shaft (=VERY small wheels)

BUT as a rule: "robots require geared down motors!!" if not, they do not work.

I always recommend high gearing (200:1 or something like that) for beginner’s projects. It makes the robot much stronger, and so it is more forgiving for bad code. And, it makes it slower, which makes it easier to capture what on earth it is doing so you can debug.

I know it may sound like fun to start with a fast robot, but it is not! On the contrary, the slow ones are fun! Check my first robot, I think the gearing must be something like 400:1 (pre-assembled 200:1 gears, and then I double up with extra gears).

There is a ton of very fine articles etc on the more deep thoughts on gearing out there on the net, so I will not go into that.

But for robots:

You can get a million different geared motors. Some you assemble yourself, and some where you can change the ratio. Pre-assembled little packs are very popular, and a good idea is to buy wheels that match! It will make you happy not having to drill or glue to get the motors to fit the wheels!

Thank you so very much to jklug80 for helping making my english somewhat understandable in this text :)

Hope it was helpful, Have fun :)

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
TheCowGod's picture

That's a great idea for a project -- try to build either a CVT transmission (two cones with a belt in between) or just a regular geared transmission from scratch. I might actually put up a challenge for that.

Dan

fritsl's picture

Mighty awesome!

I think the price should be a picture of you! Straight up. Signed on the back!

Or perhaps something you have made en clay, but that may be expansive to mail.

Would be cool to see how far people would go for a signed picture of you. Personally I think I would have a good look at the challenge! 

jklug80's picture
I think Frits is in love...
fritsl's picture

2 cones opposite, a band between.. I have tried to make it. I would love a robot with strong powe to start, and high speed later.. Just did not have the tools to fabricate it!

-<-
->-

Band from < to >, and "-" are axels. The band would wander from one end to the other, depending on speed, would be so cool.. 

fritsl's picture
Casca - could you make something like this?
psy's picture

Quite apart from just not going anywhere, attempting to drive a motor that cannot turn can damage it as well. It's worth noting that the amount of torque and speed you have are directly in competition. You can choose to divert from one to the other.

It's also easy to work out how much you will loose and gain. If you have a ratio like 75:2 then every time the motor turns 75 times the output will turn twice. Diving one by the other this means the speed has dropped by 32.5 times, but the force exerted at the wheel has increased by that amount as the total energy is the same. This of course ignores the loss of energy due to friction, back EMF etc...

sciguy77's picture
Frits,
 
This was very helpful, thank you. 
 
 
Brennon 

 

“Our deepest fear is not that we are inadequate. Our deepest fear is that we are powerful beyond measure. It is our light, not our darkness that most frightens us.... -Marianne Williamson