motor sequencing from 74xx chips...

motor sequencing from 74xx chips...

Postby techhobbit » Mon Nov 05, 2012 3:12 pm

((This has been answered by Alex's recent update/repost.))

Hello everyone,
I had this post on a previous 7400 Competition project (Alex's Most Useless Machine - nice job Alex!!), and was afraid it would never be seen...

techhobbit says:
November 2, 2012 at 5:48 pm

Hi DP, and Alex…
I like this! I’ve sequenced motors like this but didn’t use logic gates… I’m just curious as to the control… is the schematic available? …or a simple explanation of the control? Are those servos or just motor/gearheads with a lot of limit switches?? Is Alex still around?
I’d be glad to hear whatever anyone else would like to add…
If servos, then logic gates would have to trigger, or generate, the servo pulse signals...
or a series of sequential flip-flops could drive each step...

Can/would anyone please assist?
Thanks.

If anyone is interested, my project – Most Useless Robot Ever, is here:
Oops, I can't put link in here 'cuz I'm a newby....just look up Most Useless Robot Ever on youtube.
(I know… its got some minor jitter problems due to weight/small motor mismatch…I did this motor sequencing with nothing but motor/gearheads and limit switches, and a DPDT switch.)

Thanks,
techhobbit
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Re: motor sequencing from 74xx chips...

Postby Alex555 » Mon Nov 05, 2012 11:25 pm

Thank you. I guess I kind of left out some very important information. I currently do not have a schematic, as I made this circuit on a wire wrap board with no planning because my breadboards were all taken up, but I can make one if you would like. I did use four servos, and a 555 circuit, which is the only part of the circuit that I got from online, because my original circuit did not work, but that was because of a wiring error, which I later proved because my design worked on a breadboard. I just used a 74hc4514 to switch power (through diodes) to resistors. The resistors are connected to the 555 circuit, and their value determines the position of the servo. The circuitry to sequence through the resistors is made of a 555 and a '161. This allows me 16 sequences, of which thirteen I used. To control which servo drives, I have 4x '151 multiplexers selecting data from four eight bit dipswitches. This is then fed into a '138 demux with the enable tied to the servo control output. One very important detail is that since I have the resistors driven through a diode, I have the 4514 that drives it at 5.6v, the rest of the circuitry is at 5v. I just used a diode to drop 5.6 to 5v. It will not work properly without the voltage difference. The attatched file is the servo control circuit, but the values I used are different. I will do some reverse engineering and create a complete schematic.
schem.docx
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Re: motor sequencing from 74xx chips...

Postby techhobbit » Tue Nov 06, 2012 3:08 pm

Thanks for the reply. I understand the -161 1-of-16 used as a sequence stepper. And I think you just gave me the part I needed to see - the servo driver. I understand the signal (1-2msec pulse train)to drive servos... but not sure how you integrated the two - if it is explained above, and I didn't catch it - sorry... I will look it over again and crack open my ref materials. If you get a chance, and still want to do a schematic, I'd love to see it. I think if I saw just one channel, from output of -161 to a servo, I'd be able to do the rest. I am especially interested in being able to sequence servos - exactly what you are doing - whether its TTL/CMOS or something else, doesn't matter so much. I know these days there is a strong advocacy for learning microcontrollers; I've dabbled with them, but I'm more old school...
Thanks.
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Re: motor sequencing from 74xx chips...

Postby Alex555 » Tue Nov 06, 2012 6:55 pm

I know what you mean. I rarely use microcontrollers on projects. Come to think of it, I never have. I will have a schematic of just controlling one servo. would you like one for controlling multiple servos as well?
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Re: motor sequencing from 74xx chips...

Postby Alex555 » Tue Nov 06, 2012 9:25 pm

Here is the part of the schematic that sequences one motor. After several attempts converting the schematic to an image (curse you, demo version!) and printing to virtual printers (who calls something an 'image writer' when it only works for text?) I finally hit the print screen button that few people know what it does, and cropped it in word. Also, if your robot (which is quite cool, I must add) is having jitter problems, use counter weights or springs. My useless machine has a spring to keep a servo from hurting itself driving too far, a spring for keeping the side door shut, and a spring to hold up the arm while the servo is not driving. It even reduced power consumption. You can also bend springs if you have pliers to the exact shape you need and they still work. I would also recommend reading the writing in the schematic before anyone attempts to build it.
servo sequencer 1.doc
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