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Topic: Cheap caterpillar robot platform restrained at custom office (Read 233 times) previous topic - next topic

HermannSW

I have done >200 China orders (mostly aliexpress.com, sometimes banggood.com) in the last two years, mostly with free shipping. I ordered microcontrollers, motors, electronic components, ... and all (but two) arrived without issues at my home. They contained a stamp "freed from customs clearance" because they were too cheap.

Last week I got mail notification that one of my orders was restrained at Heidelberg custom office. They did not believe the value mentioned on the parcel (8$), and the size of the parcel got their attention. On the phone they explained that often plagiarising products are sent this way from China, and those are prohibited.

They were right with the value, the caterpillar robot platform did cost 22.90$ (only), but that was less than the value where I would have to pay German VAT.

I should bring my bill with details and open the parcel in order to decide how to proceed.

On Friday morning I took train to Heidelberg, presented the detailed bill, opened the parcel, and had to pay nothing, but could just take the parcel home. Reason was it was no plagiarism, and below the VAT threshold, any VAT below 5€ will not be taken. In Germany we have 19% VAT, which means that any product cheaper than 25.31€ or 28.08$ does not need VAT to be paid.

So I went back home with train, adding 14.30$ train tickets to the 22.90$. I have many different robot platforms at home, but this was my first caterpillar one.

A first functional test without microprocessor with 4V turning on same location went well:
https://www.youtube.com/watch?v=9Ygm0Oxhf8c&feature=youtu.be


Today I did a second "straight" test, again with only 4V of a single 25C LiPo (motors can take 3-9V):
https://www.youtube.com/watch?v=yUcnWbPxAoE&feature=youtu.be


Counting the tiles and single steping youtube video time showed 1.05m/s with only 4V:
Code: [Select]
$ bc -lq
sqrt(9^2+1.25^2)*0.315/(38/14)
1.05449957813359675047



Hermann.

Cactusface

Hi Hermann,
                  Very nice but how and why are you using one of MY videos, of MY Pololu tracked bot!!

This one: https://www.youtube.com/edit?video_id=9Ygm0Oxhf8c That used a PIC in the days before I got in to the Arduino...

OK so I can help if you need it, perhaps.
Regards

Mel.
Open your mind! But not too far, your brains might fall out.
Also like Photography, model building and my 300+ Cacti and Succs.

HermannSW

Hi,

I corrected immediately after posting, both links above are correct since then.

HermannSW

I did add a 2nd Lipo and measured straight speed with 7.5V.
Single stepping youtube video shows 9 frames per second.
Here you can see that caterpillar robot does more than 2 tiles in 2 frames.


This shows that robot speed is greater than 2.8m/s or 10km/h:
Code: [Select]
$ bc -ql
sqrt(2^2+(1/8)^2)*0.315/(2/9)
2.84053171257711009556
sqrt(2^2+(1/8)^2)*0.315/(2/9)*3.6
10.22591416527759634401


The wall crash less than a second later should make me rethink whether to do more of these ...

Hermann.

P.S:
Doing 640x480@90fps slowmo video with Raspberry camera would reveal more details.

HermannSW

OK, I added an Arduino Uno with motorshield v1 to caterpillar robot platform. A first test did work, but the 7.5V from two Lipos in battery compartment got reduced too much (5.19V/5.36V from 7.5V by Arduino Uno and motor shield's L293D motor controller) for good speed.

I added a third Lipo, but battery compartment was already full by the other (bigger) Lipos. So I just piggybacked the 3rd Lipo:
https://www.youtube.com/watch?v=gj-LMJlrIm8&feature=youtu.be


There is still voltage reduction, down from 11.22 to 8.84V/8.70V for one of the motors (forward/backward). Not sure yet why the robot got slower at the end. Voltage dropped from 11.22V to 10.80V.

Hermann.

HermannSW

Yesterday I wanted to follow up on the slowdown at the end of the video.
I replaced the three lipos used with a single 900mAh 3S/11.1V 10.0Wh 25C lipo.


Again, after 20 seconds or so, caterpillars did not want to move.
I noticed that the L293D used for M3 and M4 got very hot.
Measurements showed that while 3S lipo had >12V, the motors got less than 1V at maximum.

So the motorshield v1 seems to be incapable of driving the platform motors, because it can deliver 600mA maximal per motor.

The caterpillar robot platform description does not say much on the motors (Motor model: 260). I found many "260" motor datasheets, and many may be the ones of that platform. A week ago I opened the platform and extracted one of the motors, but there is nothing printed on it that would identify the motor:


But all the different possible motor models have one feature in common, 1A or higher at maximum efficiency.

Will try motor shield v2 next, it has TB6612 MOSFET drivers with 1.2A per channel, and if that does not suffice, try the other 3 or 4 motor controller types I have at home.

Hermann.

P.S:
Good that I have L298N from image with caterpilar robot platform at home:
https://ae01.alicdn.com/kf/HTB17drxMVXXXXc2XVXXq6xXFXXXb/202035663/HTB17drxMVXXXXc2XVXXq6xXFXXXb.jpg?size=136667&height=1000&width=1000&hash=8522d51c237e26c9852e99c60752ef09

Its datasheet says that 2A can be delivered for DC operation (absolute maximum ratings).

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