go_away

Author Topic: What about Polulu?  (Read 1093 times)

0 Members and 1 Guest are viewing this topic.

Offline BotzorTopic starter

  • Jr. Member
  • **
  • Posts: 11
  • Helpful? 0
What about Polulu?
« on: July 15, 2013, 04:54:35 AM »
Are they selling high quality parts?

I'm primarily interested in their metal gear motor:
http://www.pololu.com/catalog/category/115

Anybody who checked if the rated performance on the motors seem correct?

Their stuff is kind of expensive, does anybody know a supplyer with similar motors but better prices?

Offline jwatte

  • Supreme Robot
  • *****
  • Posts: 1,343
  • Helpful? 81
Re: What about Polulu?
« Reply #1 on: July 15, 2013, 10:10:17 AM »
I love pololu. They test their stuff before they sell it, and they support it in their forums. I am a happy customer of theirs.

The reason they are not as cheap as the Chinese direct sellers, is that they actually do test their stuff, and they actually do support their stuff. That means they have to pay more salaries, which means they need a larger margin. I wouldn't call them "expensive" by any stretch of the imagination, though -- the same performance gear bought from a commercial motion control company would cost between 2x and 10x as much!

I've used their 37D gearmotors with encoders, and they perform as advertised. I've also used their micro metal gearmotors, and they also perform as advertised, although the warning about not soldering contacts for too long is not kidding -- the plastic melts easily and ruins the placement of the brush on the inside of that contact. (I found this out trying to de-solder from it.)

I also really like their pre-crimped wire/cable harnesses, and their switching voltage regulators, and their motor controllers (H bridges.)

Offline BotzorTopic starter

  • Jr. Member
  • **
  • Posts: 11
  • Helpful? 0
Re: What about Polulu?
« Reply #2 on: July 15, 2013, 05:06:29 PM »
That sounds great!

I thought they were some random far-east company when I just read the name, but now I saw that it was started by students from MIT.

Was it possible to overpower the 37D motor you think?

The 25D motor has almost the same stall torque as the significantly smaller micro-gear motors. I wonder if one of these two are under- or over their specification.

Offline waltr

  • Supreme Robot
  • *****
  • Posts: 1,944
  • Helpful? 98
Re: What about Polulu?
« Reply #3 on: July 15, 2013, 05:18:28 PM »
I also really like Pololu and their gear motors. I haven't used to ones you linked to but have used their small gear motors. These met and exceeded the published specs. Many times this is not the case for any China direct parts if there are any specs at all.

The prices for their stuff (gear motors included) I think are very reasonable. An equivalent gear motor from Micromo
http://www.micromo.com/
would start at a couple of hundred dollars.


Offline jwatte

  • Supreme Robot
  • *****
  • Posts: 1,343
  • Helpful? 81
Re: What about Polulu?
« Reply #4 on: July 15, 2013, 08:36:41 PM »
Quote
Was it possible to overpower the 37D motor you think?

What do you mean? I ran them at 16V, and they ran fine. I did not use very long durations, though, so I don't know about overheating. I'd expect you could easily overheat them with too long use at too high voltage, just like with any electric motor.

Note that with stall torque, you also have to look at RPM, and ability to remove heat from the package. Smaller motors can have lots of torque at low RPM (high gearing) and short duty cycles. Larger motors are more robust, and can have higher RPM (lower gearing) for longer runtimes.

If I remember right, some of their highest geared motors (250 - 1000 to 1) carry a warning saying that if you stall them, you'll ruin the gearbox.

Offline BotzorTopic starter

  • Jr. Member
  • **
  • Posts: 11
  • Helpful? 0
Re: What about Polulu?
« Reply #5 on: July 16, 2013, 06:43:40 AM »
Sounds good this. I ordered two 10:1 micro gear motor and some other stuff I need for a line follower now.  ;D

The torque from the 5:1 motor probably would have sufficed if driving it over stall current, but it felt better to run the motor at a higher speed at a current a bit lower than at stall.

Is my intuition correct? How warm do these motors get when running them at stall current?


Offline jwatte

  • Supreme Robot
  • *****
  • Posts: 1,343
  • Helpful? 81
Re: What about Polulu?
« Reply #6 on: July 16, 2013, 09:55:03 AM »
Quote
How warm do these motors get when running them at stall current?

Probably warm enough to overheat the motor if you do it enough. Typically, motors are not rated to run at stall current for long times.

Then again, if you solve a line following problem in 30 seconds, that might not count as "a long time" :-) Please let us know what you find!

Offline waltr

  • Supreme Robot
  • *****
  • Posts: 1,944
  • Helpful? 98
Re: What about Polulu?
« Reply #7 on: July 16, 2013, 05:39:09 PM »
Not not design to have any motor running at Stall for more than a few seconds.
The best design runs the motor at about half of stall and is where the motor runs at best efficiency and maximum output power.
Here is a link about motor:
http://www.micromo.com/dc-motor-tutorials.aspx

The Motor Calculations paper is very good as is how to select a motor.

One Bot I built uses the Pololu micro-gear motors with a 100:1 ratio. Works great.
I'll guess that you will find that the 10:1 motor, unless you add additional gearing, will be too fast for a line-follower.

Offline jwatte

  • Supreme Robot
  • *****
  • Posts: 1,343
  • Helpful? 81
Re: What about Polulu?
« Reply #8 on: July 16, 2013, 10:07:55 PM »
Quote
The best design runs the motor at about half of stall and is where the motor runs at best efficiency and maximum output power.

Actually, it's often much less than that. Good motors are rated for "continuous current" separate from "stall current."

Quote
10:1 may be too fast

That kind-of depends on how big his wheels are, and how fast he can make his sensors. If the goal is to dominate the line following competitions, that may be just the right way to do it :-)

I use the 35:1 micro metals in a Zumo treaded mini-rover, and they work fine as long as I don't solder too hotly/long to their connectors.


Offline BotzorTopic starter

  • Jr. Member
  • **
  • Posts: 11
  • Helpful? 0
Re: What about Polulu?
« Reply #9 on: July 17, 2013, 03:58:56 AM »
waltr: That was an informative page.

I've seen that the fastest the fastes line followers in Europe offically average around 2-3 m/s and got a peak speed slightly over that.

I don't know if it's realistic yet but I therefore aimed at a top speed of 5 m/s for a certain victory or at least a very  powerful crash  ;)

With my wheel size the 10:1 motor is reving a whooping 30 000 rpm when driving 5 m/s which must be rather extreme for a brushed motor.

However,  I dont even have a slight clue about possible mechanical losses from wheel friction etc. If those tend to eat more than a few mNm, the 10:1 was the one to go.




Offline waltr

  • Supreme Robot
  • *****
  • Posts: 1,944
  • Helpful? 98
Re: What about Polulu?
« Reply #10 on: July 17, 2013, 07:41:18 PM »
Ok. Please do keep us updated on how your project progresses.

 


Get Your Ad Here

data_list