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Help with Micro/Mini Gearhead motors for tiny bot

Ok so if you've read my profile here, one of my goals is to create/produce a low cost, versatile micro/mini robot that could be used as a swarm bot.

Currently I'm trying to source some decent tiny gearhead motors for under $12 dollars. Today I've come across these:

http://goo.gl/H17Wj

and this

http://goo.gl/0U1bf

 

Also there are some 3V gearmotors of the same dimensions with varying RPMs (from 30 to 100rpm) available as well. The torque ratios are not given for those, however.

 

Now my question to all of you is, which motor(s) do you think would be better for this project?

Here are some details:

2" x 2" plastic platform

12mm diameter wheel (approximate)

All combined (electronics, motors, battery, platform), we're probably talking weight in the ounces.

What do you think would be a decent RPM speed? And if I go with the 6v motors do you think I could get away with feeding them around 4.5 volts? I've seen some similar gearhead motors that accept voltages ranging from 1.2 to their max 12vdc. Not sure if all motors are like that or if some have specific vdc required.

Any help would be appreciated!

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these guys are in the same price range, just a bit higher on some things than ebay, and have over 1000 choices for spur gear motors, 50 rpm might be a little slow depending on wheel size CTC line follower uses 120 rpm, I know its larger but I would want to go atleast 1/2 that fast, so at 50rpm ya need wheels that big, and 3v would be cool, only need 2aa or aaa, they also have usa offices if that helps

 

http://www.kysanelectronics.com/Products/Catsub.php?recordID=3

ossipee

let me amend that he uses 120 to 1 ratio motors my bad sorry

Actually I just received some micro 9g servos, and these things are TINY! I may just go with servos--cuts out the need for an H-bridge since the MUC can control them directly.

Direct control from the MCU is a big plus but the problem with servos is the robot gets pretty wide when you put them back-to-back.  These's a good design for a tracked robot HERE using 9g servos and Pololu parts which alternates the drive and idler wheels to reduce the width.

Oh wow that's a really cool robot! Thanks for the link. It's almost practically what I'm trying to do. Except I think I can get mine even smaller.

Here is what I used for my 50mm square robot.

http://letsmakerobots.com/node/21895

Wow very nice Gary! Just checked out your 'bot details. Interesting design and fabrication. The gearmotors you're using seem to be even tinier than the ones I'm looking at, but they're also 1.2x more expensive :(

Ultimately my bot should come in at approximately $40 dollars total, and that's just with off the shelf, pre-fab components. Also I see you're using metal hex standoffs for the frame/levels... have you considered using nylon standoffs for lighter weight instead?

If 300 rpm is not too fast the how about these? Price is good. You could always pwm to slow them down.

Or smaller ones, similar price

I guess if your building one for a prototype, price is not too important but then if you want to build ten or a hundred then it really does matter a whole lot.

I'm wondering about those gearmotors on a 2" x 2" chassis. They are 26mm long without the shaft allowing a 5mm gap for the terminals at the back of them makes a width of 57mm if you mount them inline. Which is a bit over your 2 inches. if you include your wheels on shaft the track will be 79mm or just over 3 inches.

I wouldn't go under 100 rpm . You can always slow a faster motor down. You can never be sure if what is pictured is the same as somewhere else but generally the ones I've seen and the couple I have can run from 3-6v. Some say up to 12 although I haven't tried.

I was looking at similarly priced ones in your second link, however that would definitely be too long for my chassis.

I'm probably going to go with the 3v ones here: http://goo.gl/0U1bf

3v, 50rpm, 40mA current draw (I'm assuming no load) @ $6.76 a pop with free shipping.

I'm also pretty sure that they are similar to the Pololu micro metal gearhead motors here: http://www.pololu.com/catalog/category/60, so they're probably 250:1 torque.

As far as mounting, the idea is to have them parallel to each other, with two dummy wheels on the opposing ends for balance.

That gives me 26mm motor length + 9.5mm shaft length + 5mm gap for terminals = 40.5mm or roughly 1.6 inches.

If I can find +100rpm versions of this motor I'll try.

50 rpm should be ok. They sure do look like the pololu gearmotors don't they? So that's a good saving on the regular price. They are a smooth motor too, not noisy and not hard on your motor drivers.