Motor Test Station (MTS)

Using Arduino Motors, Mechanics, Power and CNC
41

OK, I rebuilt the Motor Test Station.

First I turned the base board, there were too many holes.
And to avoid the base board from moving as in the end of last video, I used nails in the corners to fixate the base board on the desk (click on the photos to see more details):

Here you can see the replacement for the safety glas surrounding.
I hope that the4 fixing brackets will avoid bullet plus motor to go throug the wall from now on:

This is top view from Raspberry camera, which normally takes the 90fps videos:

Finally I replaced the wooden motor mountings with plastic.
I hope that it has same behavior as wood wrt vibrations, but is more stable than wood:

Test runs would be too loud now at night here, will do tomorrow,

Hermann.

42

I did a further modification to MTS, added a peephole for third Raspberry NoIR camera to take horizontal video for bump analysis. More details in forum posting 1ms shutter speed 90fps slowmo dark – not with NoIR camera!

I started like most others with aluminum outrunner motor mounts, but with what I do I always break these:

Next step was to use self made mounts of wood, but they splittered:

Next was to use self made motor mounts from plastic, a really bad idea. At least the plastic I used was too brittle and quickly just broke:

Next I tried to go back to my roots. Normally I do (nearly) everything with superglue, and so I did here as well, I superglued A2212 outrunner motor to beaverboard ...

... and then superglued beaverboard to robot wooden beam:

I had to cut a center hole into beaverboard because of the outrunner motor moving parts. In order to do minimal stress to beaverboard, I created the hole with soldering iron:

This is the final robot motor wheel connection:

I have already done many runs with the new superglued outrunner motors in motor test station, now its really reliably, and the robot ends a run as he did start, with all wheels and motors attached :wink: My explanation for this is that the (metal) base area of A2212, even without the round center moving part is so big, that supergluing that whole area to beaverboard is much better than 4 screws:

Last, but not least, some 90fps slowmo video action :wink:
Click the animated .gifs to see in 640x480 size.

From peephole 90fps slowmo video: Robot starts with spinning wheels, bumpy, but goes smooth later. Animation is slowed down by factor of 10:

https://stamm-wilbrandt.de/en/forum/out3.anim.gif(image larger than 4 MB)

And a reminder to myself: "Don't forget safety glas cover on Motor Test Station!"
Wheel lost at 52km/h hits wall, then goes up out of MTS, near miss of top camera!!
(1 frame of 90fps slowmo video per second, slowdown factor 90)

Hermann.

43

Two days ago I did a further run, but that run was different, robot did go wild. The Arduino sketch should run the robot for 10 seconds and then stop, letting robot roll out to stand still. For yet unknown reason the robot repowered again and again, starting the 10s cycle without stop. Speed was far to high to stop robot by hand. Had to wait for 5 minutes until robot stood still so that I could cut power. In the end the digital voltmeter on robot showed less than 9V under motor load. It shows 12.1V without load, so the 3S 11.1V LiPo was not empty. During the whole run the robot smelled like some cables roasted, after the end I was able to locate the smell on mini breadboard where all the cables are connected:

Yesterday I unscrambled mini breadboard cables and uncovered a reason for last run bad smell, the blue, 2nd ESC GND cable got burned, too many amps:

Further unscranbling of mini breadboard cables revealed, that mini breadboard does not like too many amps either :wink:
[left and right column, bottom 3 connections]

Time for recabling and not using breadboard nor breadboard cables for links that get several amps, and to use a real power on/off switch,

Hermann.

P.S:
At fastest run the robot did 18.77/1.28=14.66rps or 880rpm. Vertically mounted Arduino Uno had no problems to operate at 14.66rps, and I suspect the not perfectly plugged in AWG power cable to be the reason for robot going wild and not the Uno.

44

I did all the MTS rps/rpm determination with 90fps videos because I did not know that Raspberry cameras can be talked into doing much higher framerate videos (up to 750fps with 6$ v1 China clone 5MP camera, up to 1007fps with 30$ v2 8MP camera)!

With Motor Test Station rpm always was in 3-digit range and 90fps was more than enough. Recently I successfully determined the rpm of RC airplane with 1007fps video as 20140rpm. Just wanted to post here in case others need/want to visually determine fast rotational speed. This is 640x75 video recorded at 1007fps, played at 1fps:
https://www.raspberrypi.org/forums/viewtopic.php?f=43&t=190407&p=1319617#p1319617

Very high framerate means low shutter time, so very bright light is needed, I used 5000lm led here:

2560×1920 587 KB

47

I created a 2nd version of caterpillar robot platform last year, "raspcatbot" because there is a Raspberry Pi 3A+ onboard controlling the motors and analyzing the 320x240@204fps Arducam monochrome global shutter video stream for automatic high speed line following. I paused that project last June after having achieved acceleration from stand still to 2.55m/s followed by full speed reverse powering braking on 4.5m long hardboard inside room. Because I had not written the line following code, I superglued two M3 nuts below robot front and back and made it a cable car. The visual real time end of black line detection and then full brake algorithm did work though:

Jacked up robot free running speed is quite high (1774rpm), with 65mm wheel diameter that was 6.04m/s free running (I did superglue small stripes of red foam rubber to endless track in order to increase friction for very short area full braking):

692×519 175 KB

I did restart raspcatbot work in June and had to ask to unlock the aged thread on Raspberry forum, as well as today this thread on Arduino forum.

I did place a big screw in my garage floor center and added 2mm ⌀ steel wire cord to raspcatbot in order to see maximal speed achievable. After seeing only 66% of theoretical speed I identified the cause, I used Pi3A+ 3.3V pin to control 5V logic level L298N motor drivers. I increased makeagif.com playback speed of 2.8m/s run with 1.150g raspcatbot by factor 1.5 in order to see how 4.2m/s speed will look like after adding logic level shifters between Pi3A+ and L298N -- looking at this makes me feel giddy:

Target is to run 1kg raspcatbot (with only one 4S 1.3Ah 95C lipo instead of two) with 5m/s in garage. on 1.25m radius. The steel wire chord seems to be able to deal with computed 20 kg*m/s² centripetal force. I computed kinetic energy for that scenario as well as 12.5 Joule(!).

Then I remembered the outrunner motor high speed record run in this thread, where "outrunner motor+Lego wheel+bullet" (72g in total) did cut loose at 18.77m/s speed and destroyed MTS front safety glass. I was totally surprised that this small pack had even bigger kinetic enery (12.68J) than raspcatbot at 5m/s will have:
https://www.raspberrypi.org/forums/viewtopic.php?f=37&t=267999&p=1887701#p1887701
Just wanted to add this kinetic energy computation for the incident from 4 years ago, becuase it belongs here:

P.S:
Wow, I did not add the computation of centripetal force for 72g pack in the other thread. But just saw that the big wooden bar was a must in order to deal with 122.25 kgm/s² centripetal force (mv²/r -- in comment 40 diameter was 41.5cm):

$ bc -ql
0.072*18.77^2/0.2075
122.24833156626506024096

Likely the big wooden bar between 72g pack and rotation center will add centripetal force to total centripetal force one arm of circular robot has to handle.

48

Hi, @HermannSW :+1: :+1: :+1:

Thanks for the update.
I am surprised at the speed you can get from the tracks.
Still using L298N, it would be interesting what you could attain using a more efficient motor driver.

Tom.. :smiley: :+1: :coffee: :australia:

1 Like
49

Still using L298N, it would be interesting what you could attain using a more efficient motor driver.

Even after more than 4 years I am still more the experimental guy trying things out before really understanding them.

I learned that the (150g weight) 4S 1.3Ah 95C (monster) lipo I use to power the robot can continuously deliver 1.3*95=123.5 amps. When buying 3 of those I bought a lipo safety bag for charging those lipos for the very first time.

Regarding the motors, I think you will not like what I will do after adding voltage level shifters. Fully loaded the lipo has 16.8V, and because of my 3.3V vs 5V logic mistake the L298N motor drivers maximally did put 16.8*2/3=11.2V onto the 12V 1500rpm gear motors I have replaced the original robot platforms 330rpm 12V motors with (surprising that the 12V 1500rpm motors shows 1774rpm free running when only powered with 11.2V). I will have to see how the gear motors will react when powered with more than 12V ...

The L298N module(s) I use seem to be an additional bottleneck, while able to deliver more than 30V and up to 2A per channel, they only provide 25W (per channel?). That is no problem when powering with 11.2V erronously as I did, but 25W/16.8V is only 1.5625A.

What motor driver alternatives do exist (I have no data how much amps the 12V 1500rpm gear motors draw)?

P.S:
The maximal speed for 1kg raspcatbot in garage I captured real on video was 3.2m/s or 11.52km/h sofar. I hope to be able to add 50% using level shifters for getting 4.8m/s (17.3km/h).

50

Hi, mate.
Pololu have a good selection and data table.

Tom... :smiley: :+1: :coffee: :australia:
PS, Keep up the experimenting. :+1: :+1: :+1: :+1: :+1: