Looks like I need at least
Looks like I need at least five layers, which made the axle just thick enough to touch the wheel bearing when the band is added. So the wheel gets turned one way by the band and the other way by direct contact with the axle. Time to remount the motor a little further away.
Back where I started…
The extra tension in the right motor band makes it turn slower than the left motor when under load. I can try moving the left motor so it is equally spaced as the right, which should add some tension and slow the left motor.
BTW, I’ve accidently made a cliff detector. The right motor does turn under load, just not as fast as the left. So placing the bot on a white box under a lamp has it scooting around making slow right turns, and then turning off the right motor when it detects a cliff for a hard right turn. Pretty cute, even though it is not what I’m trying to accomplish.
Trying a version of the
Trying a version of the spurtbot with a reflectance sensors. Thanks to Spurt for all the advice. Here’s the idea:
Plans started with this version:
http://goo.gl/UzT1h with this schematic: http://goo.gl/V9Ann
Except:
- 3 V (instead of 6)
- LED resistor lower, just as needed
- Remove transistor for left motor, and just run it directly from 3V.
- First (and now single) transistor is bc337
- Right hand motor shaft thickened
Having trouble sourcing some CNY70 sensors. I can get them, but shipping costs are silly compared to the cost for the parts. I’ve requested some samples from the manufacturer, but I haven’t heard back yet.
However, I had a QRD1114, which is quite similar. I breadboarded the circuit, and it seems to be working well with a 3V Jency motor (ST-130). Just need to try a build with this setup.
Motor turns too fast, I think
Ignoblegnome, the mobile can keep its track only if the speed is not too high: let’s say about 1 ft per second would be fine. So I think you need motors which turn with about 2,500 rpm at 3 V. ST130 turns with 12,500. That could be pretty too much. And it might be that the transistor will not have enough current gain for this motor.
Might be those motors could be worth a try: http://goo.gl/gpri0 or http://goo.gl/Vm6Yk
This model may be viable.
This model may be viable. The QRD1114 seems to work OK. I did need 3 widths of 3/4 inch electrical tape to make the track, otherwise the spurtbot doesn’t react quickly enough and jumps the track.
Also the batteries (2xAA alkalines) seem to have run down pretty quickly.
Thanks. Actually the motor
Thanks. Actually the motor referenced turns at 5200 rpm at 3V under no load.
I took a look at the motors you referenced. They might be good. Maybe I’ll order a couple each and try them out.
Thanks again for all of your help!
Oh yes, you are right, this
Oh yes, you are right, this motor might work pretty good. 2600 rpm with load sounds reasonable.Current could be a bit less but at least it should work if you have a transistor with enough gain. Congratulations, now I am keen to see a video.
There is no big difference between QRD-1114 and CNY70, so you can use each as well.
33 Ohm for R1 seems to be fairly risky, you will get a froward diode current of about 50mA, which is the limit already. Might be you could consider a higher value for this resistor.
Don’t you think that R2 and R3 could be dropped? Or have they a beneficial effect?
I might be operating a bit
I might be operating a bit close to max current on the IR emitter. I may try to increase the value of that resistor.
I tried the circut without the 1.2k ohm resistor at the base of the transistor, and it did work OK. It seems slightly less reliable and responsive to the white/black transistions.
Maybe I’ll breadboard another copy of the circuit and see how it works if I eliminate those two resistors and increase the current limitiing resistor.
Thanks again for all the feedback. I did shoot some video yesterday, so I’ll get it posted soon.
As a very slight
As a very slight modification you eventually might consider to connect R1 to pin 4 (instead of pin 3)? This way you could connect pin 1 and pin 3 directly at the QRD 
If you look at my build
If you look at my build diagram, you will see that I route the ground from the emitter of the bc337 to pin 4 of the QRD, and then to one side of R3 for the pull-down resistor.
If I eliminate the 10k pull-down, your suggestion makes sense. If I keep it, it is actually convenient to route the way I have it.
I need to order some more parts so I can test out the alternatives you suggested (removing R3 and R2).
The TIP120 transistor seems
The TIP120 transistor seems to be a good choice, this way you have enough gain and don’t need too much LED current.
I’m much happier with my
I’m much happier with my QRD1114 based design, which happens to use the bc337 transistor. It would probably work with the TIP120 just fine too, but I haven’t tried it.
All seems to be fine now:
All seems to be fine now: When your Motor FK-260SA-10400 has enough torque with 3 V then you got it: reasonable costs, shaft long enough for the belts, not too much current for longer battery use, low enough speed to remain controlled - that’s all you need.
I hope so. I’ve ordered
I hope so. I’ve ordered enough parts to make 50 SpurtBots. It will be fun building them with people at MakerFaire.
Thanks for all of your advice!
One surprise I got was that
One surprise I got was that I didn’t have to thicken the shaft of the right motor on the version with the FK-260SA-10400. It happened to pull slightly to the left anyway. Maybe I just lucked out with some variation in the motors.
I added one layer of heat shrink, just to be sure. I guess some individual tuning may be needed, as you told me in an email.
Thanks a lot for your nice
Thanks a lot for your nice video. I wish you a lot of success at the MakerFaire. By the way - concerning the track I prefer to let the robot run counterclockwise at the outside of the track. Maybe it’s a psychological effect, but I find it a little bit more exciting to see the robot being this way attracted from outside (instead of feeling to be “caged” within the track). And if you put the track on a desk near the edges it might also be exciting to see that the robot does not fall down but unweary keeps to follow its track.
I’ll try that out. My test
I’ll try that out. My test track was small with raised edges, so it was better to have it inside so it didn’t hit the raised edge. At MakerFaire we’ll have a bigger, flat track, so it will be possible to use the outside track.
Very nice and well
Very nice and well documented as always Andrew. Thanks for sharing and way to go
See you at the Maker Faire
If you get the Mabuchi motors in time for the Maker Faire, I’ll be one of the earliest people in line to make my first robot. If not, and you end up with a surfeit of them, I’ll be happy to buy a set of parts from you for at least twice what you pay for them plus shipping.
Parts should arrive in time.
Parts should arrive in time. See you there!
