Advice on DC Motor...

Hello all

I'm new to hobby electronics and Arduino - so be gentle with me :)

I set myself a target of building a wall avoiding robot, so thought I'd buy a car chassis kit to start me off, this one in fact: https://www.sparkfun.com/products/10825

The motors (48:1) seem woefully underpowered, and the bot struggles to move around my lounge carpet.

Now I was thinking of getting these motors as replacements: http://www.hobbytronics.co.uk/motor-control/motors-general/mm-gear-motor-100

Now, my questions are: 1) Are my choice of new motors a good one? 2) What exactly does the ratio mean with regards to these type of small DC motors?

I'd like the bot to nip around my floors quite quickly, not moving like a slug and failing to turn!

All answers gratefully appreciated!

:)

How are you powering the motors and motor controller? Which motor controller?

Carpet isn't easy to move on. Part of the problem is that huge ball roller. It is heavy and will tend to sink into carpet. I suggest making something out of delrin, something much flatter and larger in its contact area with the carpet.

The wheels should also be larger diameter. If this only has to move on carpet, something hard with some short spikes.

On second thought, I'd redesign this from scratch. Look at a Roomba: Nothing small and heavy is pressing into the carpet.

polymorph: Carpet isn't easy to move on. Part of the problem is that huge ball roller. It is heavy and will tend to sink into carpet. I suggest making something out of delrin, something much flatter and larger in its contact area with the carpet.

The wheels should also be larger diameter. If this only has to move on carpet, something hard with some short spikes.

On second thought, I'd redesign this from scratch. Look at a Roomba: Nothing small and heavy is pressing into the carpet.

Yeah, I thought that also, I was hoping that a bit more oomph from the motors would alleviate the problem.

My other idea is to find a cheap radio controlled car, strip it apart and use it for parts.

MarkT: How are you powering the motors and motor controller? Which motor controller?

Hi MarkT, I'm using an Arduino Uno, and the official Arduino Motor Shield.

I'm aware the L298 is a voltage sponge, I've got 4 AA batteries (6 Volts) and the voltage going to the motors via the L298 is about 4 Volts. So I rigged up a test and forced 6 volts to the motors to do a quick test to see if the extra voltage would give the motors more power (then the plan was to purchase a voltage regulator), but still the motors got stuck.

Apparently (having done a bit more research) other people are saying the motors suck.

From another persons reply, I might consider starting off with a different chassis, and ditch the caster wheel...

Yeah that's a crap chassis, gfpo.

I also found that those "tyres" (or "tires", depending on where you live) are very slippery although they look tready. They're quite hard and shiny. Maybe try a bunch of rubber bands to increase the traction?

JimboZA: Yeah that's a crap chassis, gfpo.

I also found that those "tyres" (or "tires", depending on where you live) are very slippery although they look tready. They're quite hard and shiny. Maybe try a bunch of rubber bands to increase the traction?

Hmm, yeah, I'll try the rubber band idea.

BTW, what does "gfpo" stand for ?!

Good For Parts Only 8) The little screws and spacers are nice, and the laser cut plastic with all those holes and slots might by handy.

Apparently a code in the margin of patients’ charts among the medical fraternity.

JimboZA:
Good For Parts Only

Ahhh!
And there was I thinking it was a new expletive acronym I hadn’t heard of :roll_eyes:

Mind like a sewer.

NewHobbyist:

MarkT: How are you powering the motors and motor controller? Which motor controller?

Hi MarkT, I'm using an Arduino Uno, and the official Arduino Motor Shield.

I'm aware the L298 is a voltage sponge, I've got 4 AA batteries (6 Volts) and the voltage going to the motors via the L298 is about 4 Volts. So I rigged up a test and forced 6 volts to the motors to do a quick test to see if the extra voltage would give the motors more power (then the plan was to purchase a voltage regulator), but still the motors got stuck.

Ah well, I was wondering if the 2V or so lost across the L298 might have been the issue..

The two things you have to get right with sizing motors is enough torque to overcome losses (gearing, friction) and still move the chassis up slopes, and enough power to do so fast enough... A lack of torque can be cured by more reduction gearing, a lack of power cannot.

It's 2v (1.8 iirc) at no load, rising to almost 5 iirc, under heavy load, which you might get at a stall.