Go Down

Topic: New robot:battery drainage advice, mechanical design improvement (Read 3 times) previous topic - next topic

supercap

Heres some more info:
speed (noload)=24000
speed (load) =18000

1.98 is max current w/load. Part # 273-256.
So I should use gears? What would you recommend? Is there a gear kit??

cr0sh


Heres some more info:
speed (noload)=24000
speed (load) =18000

1.98 is max current w/load. Part # 273-256.
So I should use gears? What would you recommend? Is there a gear kit??


1.98 amps - definitely won't get that out of a 9V battery for long!

Gears would be ideal, but unless you have some mechanical fabrication skills (or even if you do!) it won't be a cakewalk to design and build a gearbox, due to the tolerances needed so that the geartrain doesn't bind or generate excess friction. This is why I was recommending using pulleys and rubberbands or similar; much more forgiving of misalignment and errors.

Honestly, the best kits to get for small robotics use are the Tamiya gearboxes (see http://www.tamiya.com/english/products/list/educational/kit70001.htm); most can be found or ordered thru well-stocked hobby shops.

If you wanted to try your hand at designing your own gearbox, you might pick up something like:

http://www.allelectronics.com/make-a-store/item/GR-5/SET-OF-5-GEARS-AND-BUSHINGS//1.html
http://www.allelectronics.com/make-a-store/item/GR-86/4-GEAR-SET//1.html

I think Tamiya also sells a gear assortment (?). Just make sure you buy two sets (one for each motor/wheel).

The only advice I could give for homebrewing a gearbox would be to layout the gears and shafts using cardboard templates and toothpicks or similar for the shafts; then transfer the design to metal or plastic and drill through both sides of the gearbox at once (make sure to use a drill press or keep your drill vertical and perpendicular to the material). Use metal or plastic shafting for the end version (play around with stuff here - you might find, for instance, that pieces of coathanger wire are perfect). Superglue or epoxy the glues and shafts together as needed. Add some light lubricant once assembled (petroleum jelly is OK, or if you have it, silicone-based SuperLube is nice).

Good luck!

:)
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

supercap

Ok so I found some gear motors i had lying around. They opperate somewhere around 60-70rpm. I attached them to a new quasi-chasis structure w/4AA batteries. They worked very well so the original problems i had have been solved. However when i inserted them into the actual circuit i started experiencing some rather unusual problems (i had had no actual problems with the circuit with the other motors).
Perhaps i should first explain in alitte more detail what iam doing .
An analoginput on the arduino is connnected to a 38khz ir photoreciever module. The reciever picks up the transmitter, a homemade dual-555 (one 555 for carrier 38khz, the other for modulating the carrier). The signal is demodulated in the reciever and the modulating waveform goes into the analogpin.
Basically all the arduino is doing right now is interpretting the pulse width of the signal and writing the output accordingly. The hightime(0 - period) is mapped from 0 - 255 (pwm of one motor). The lowtime (0 - period) is mapped from 0 - 255 ( pwm of other motor). The pwm values are also written to two leds that act simply as indicators.
The first problem that im having is that one of the geared motors seems to "overpower" the other. That is to say that once i turn on the "superior" motor i am unable to switch back to the "inferior" motor. Could this be because of the motors inductance and that it is pulling current away from the other motor? This is what i thought but then i saw that the indicator leds were also biased in this way. How is this possible if the leds are a completely separate circuit from the motors. Could the problem be magnetic interference? I looked through a scope and saw a lot of interference whenevr the motors were connected.
I also noticed (from looking at the indicator leds) that the transition from one motor to another when the pot was turned slowly was not smooth. Im pretty sure that this is related to the first problem .

I may upload some pics/vids if they would be helpful.
Sorry if my questions are getting annoying. And for the wordiness of my reply.
Any ideas would be welcome.

supercap

#13
Mar 20, 2011, 04:19 am Last Edit: Mar 20, 2011, 05:34 am by supercap Reason: 1
just tested the gearmotors again (with no load) and they seem to be working fine with the arduino program (smooth transition, no "overpowering" motor). I dunno maybe it's chronic...
--------
just a note, i didnt use any ir protocol, just modulated the carrier.

cr0sh

If you're getting noise, you'll want to put some small value non-polarized (ceramic disc is fine) caps across the terminals of the motors, and perhaps even from the terminals to the case of the motor; you might need to go so far as to isolate the motor driver from the Arduino using optocouplers. I'm not sure if noise was causing your issue (though you say it went away?), but it certainly can't hurt to try to eliminate or reduce it if you can.
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

Go Up