Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: Kagi on January 13, 2008, 11:39:26 PM
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Long story short I ordered the servo's for the $50 robot from servocity. To my surprise they are unlike the ones described in the tutorial. I managed to get them to work and figured I'd post my findings and how I modified them. The changes are mostly the pot which you need to fix in position is now molded plastic, and affixed to the casing. I found that superglue didn't hold it in place, even after being left overnight. Finally I grabbed an old ruined soldering iron and ran to my poor man's fume hood (over the stove microwave with venting). You can probably guess what I did already, but I melted the plastic a bit to lock it into position. Worked like a charm for me. (don't breathe the fumes...)
On to the second part of the modification. The gear which attaches to the pot is now a solid piece of plastic which does not have a removable slot for the pot head to fit into. In order to fix this part I bored out the hole so as the square was now a circle shape. If you don't have a drill i'm sure you can just do this with a phillips screwdriver as the plastic is somewhat soft. Make sure you do this away from the rest of the motor as you don't want to drop all the shavings into the casing.
Now when trying to put everything back together you might have to smooth out the superglued area (*cough* melted plastic *cough*). A nail file works great for this. Don't let the shavings get into the casing. Reassemble and tada you're done. Plug it into your control board and make sure that it spins freely. If it seems like it spins roughly you might need to open up the casing and file some more edges down. I had this happen with one of mine.
The only other modification which i've made to my bot is I breadboarded it. I'll try to get some pictures up so anyone who is interested can see how I laid mine out. I used a 400 contact A-J, 1-30 board. Like 2 bucks from allelectronics.com. I also used some pickup rollers out of an old printer as wheels. I can't even begin to explain how happy I am with them. Plus they were free. I'm sure just about anyone can get their hands on an old hp deskjet. Tear that sucker apart and grab the ~2" rollers out of it. I think the one I used was from the late 90's. (Don't tear apart your mom's printer kids).
Anyways, I tried to check if there was a post about the servo's already up but I couldn't find anything with the search button. Most likely user error on my part though. So apologies if i'm restating that which has already been discussed. Feel free to ask questions if you are stuck and have the same issues I have. I'll try to get you all pics soon.
Oh also, the cable on my avr programmer was reversed :/ Yes Pin1 was on the red strip, but the connector was on backwards. If you are unsure and having issues like I was, I recommend using a small flat head, pop the connector apart and look for yourself which pin is located on what hole. It actually explained a lot to me as I was unaware how those little guys worked. Happy building folks.
Kagi
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thanks man that helps. please post the pictures when you can!
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yea pictures would be very good :)
do u have pictures of you modifying the servo? or a video? :P cuz i'm probably going to buy the same servos soon :) (they are sooo cheap thats why :D)
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what do you mean the programmer cable was reversed i built the $50 robot and the programmer cable was fine? also in the part about drilling the square the second paragraph you should be able to take the slot out by removing the ring that holds it in place.
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There is no ring holding the slot in place now. It's one solid piece of plastic. As for the ribbon cable, the connector was reversed on it from the position described. I"ll post a pic of it as soon as i get some time. Apologies, i've been working too much this past few days and haven't had time.
Kagi
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yea i ordered a set of two of them and they didnt look too like the ones in the totorial...
hope to see pics soon.
~smash
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;DHA HA you beat me to it, i just modified mine last night was going to write about it too
@ Trump, as i work in a production engineering workshop i am guessing that the newer servos (if yours is older or older stock) are now made as a solid injection mold unit its called cutting down on costs and and production time. Good for manufacture, bad for u if it brakes as you then have to buy a hole new one and not just the socket. its the same with most things these days if a part of something breaks brakes you got to buy a whole new unit
Although i got all the machinery (CNC mills, drills lathes) at work to do a professional job i didnt want to wait till Monday, My first servo i used my soldering iron to melt it round (messy and sticky) the second i also used a star screw driver twisting it round to make a cone shaped hole then a flat one to get it round, this was a lot better.
WARNING when you snip off the little stop on the shaft be careful my gear teeth cracked around that area ???, good thing i ordered 3 will use that one for my IR as there is still bit of the stop left. will post some pics in a minute, react it out lol.
Whats the best way to post a video clip,i guess a pic will do.
Good luck ;D
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my servos are brand new and they had a little ring inside the main gear that held in a slot for the potentiometer shaft to fit into. i did get better quality servos so maybe thats why.
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I modifed my hs-311's last night. I found that for boring out the gear that a sanding bit on a dremel tool worked better than a drilling bit. also when i clipped the stops on one of them, part of the upper area of the gear teeth went with it! hope it still works ok. if not ill buy another and use this one for the IR in the future.
also i used superglue and let it sit over night. ill check when i get home from work what happened as its all plastic now. might have to melt it down with the solder iron and sand it smooth as well.
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pomprocker, I broke mine in the same way two weeks ago. I tried but superglue didn't work . . .
Since it was a $30 servo, I just bought a gear replacement set.
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The HS-422 and 425 are much easier to modify and are still less than $15.
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i clipped off a tiny bit of my servo gear, it still works fine. My servo has karbonite gears so it might be able to hold up better than nylon gears.