25mm DC motor seems strange/unbalanced, thoughts?

#1

Hi everybody,

I recently bought two Makeblock 25mm DC motors from a reseller in the Netherlands. Running them, there seems to be a big difference between them. I have read issues others have had, and can not yet comment on whether they stall or lack torque. But one of them does not run “smoothly”. I have a comparison in the following video:

Note that the first motor seems to be spot-on correct with regards to the specifications: 200mA free-run current, which is on the edge of the “<= 200mA” spec.
The second motor in the video seems to encounter extra friction on every revolution. You can hear it from the sound (pitch going up and down) and see it on the current meter (current rising to 300mA once per revolution). Note that the only thing mounted on the motors is the light parts from the Makeblock motor kit, which weigh almost nothing so this is not the cause (shown by the fact that the other motor operates with it fine).

Normally I would not be nitpicking on a bit of extra current, but this is for a student project that has very tight power requirements. I am worried the motor will consume too much power / get hot / not deliver the required torque because of this “friction issue”.

What are your thoughts? Has anyone seen this happen? Can I contact my reseller and/or Makeblock to replace it?

Thanks!

Kind regards,

Sander

#2

Hello Sander
I am really sorry about your problem of 25mm DC motor, I will notice my collague and give you a solution as soon as possible.

#4

Hi Sander,
Sorry for the incovenience, after checked, we have confirmed the problem came from the motor itself, please kindly send us your address in details, consignee and mobile number to my email box: pioneer@makeblock.cc, we will arrange one new 25mm DC motor to you.

#5

Hi Peter and Pioneer,

Thanks very much for your quick replies! I will send you an e-mail with my details, and those of the reseller. I appreciate it!

Kind regards,

Sander

#6

Did you get the new motor? Did it help?

#7

Directly connected to the battery pack that came with the kits here’s the results of the motors. Note the letter refers to the kit. The number to the 1st or 2nd motor in that kit.

1a:180ma
1b: 200ma
2a: 170ma
2b: 190ma
3a: 180ma
3b: 200ma

Note that 1b & 3b are the highest and at points for split seconds hit 210ma.

Note that the voltage of the pack was around 8.7v. Using a fresh 9v battery with a metered voltage of 9.2v all the amps above increased by 10ma respectively. This agrees with the posts where people upgraded the battery pack to a 12v to get better results.

#8