The parts JUST got here, and I am starting assembly now. I’ll take pictures when I am done, but I don’t have a host right now.
Mike
Edit:
I ran into a slight snag. I purchased servos from a different supplier (for higher powered servos) and they are a bit taller than “standard”, apparently. Because of this, I will not be able to actually get this thing finished until I can figure out some way of adding a spacer in between the servo and the servo brackets. Anyone have any ideas?
Well- things are progressing pretty well, except for a few minor issues.
I came home from school to find my box waiting at my front door. Seeing that made my day 
.
So I take it inside and start opening it. Let me just say that whoever is in charge of packing and shipping things over at LynxMotion really deserves a raise. UPS could’ve drug this thing down the highway after running it over a few times, and I think everything inside would still be fine. I was really impressed with the packaging. Not only was it a really good quality box, but everything was surrounded in packing peanuts, individually wrapped, and then wrapped again inside larger bags. Very nice.
So after opening it all up and sorting out the various pieces into piles based on their soon to be locations, I pulled up the assembly guides on the LynxMotion website and went to work. This is about the time I noticed the quality of the brackets. The metal is thicker than I had originally thought it would be, which is a good thing. Most of the brackets I could not bend with my hands. The few parts that I could were on small/thin pieces that will be supported by other means, and not rely solely on the strength of the bracket (such as the prongs that hold the actual servo to the bracket). Once again, I was pleasantly surprised.
So I pull out my toolkit and start to assemble a leg. This is where I hit my first problem. The nuts and screws that hold the various brackets together are TINY. Holding these things steady requires the hands of a surgeon. Jim- I think you’re asking a lot to expect a college educated Mensan to have some manual dexterity. Right guys? Guys? Hello? Hmmm. Seems kinda quiet in here. I guess I’ll go get some cheese to go with my whining, then. So- because I had some difficulty putting the little tiny nuts on the little tiny screws, I ended up cross threading and/or stripping the screw on a few of them. Not a terribly big deal, as I think I have figured out a way to fix this issue.
There was once or twice that the instructions were not quite as clear as they could have been. Offhand, I don’t recall what exactly it was, but it was pretty minor. Especially with the pictures, the assembly instructions were rather good. It might have helped if I had read them. Yes, they did say lock washer. Yes, there were lock washers in the bag. No, I didn’t put the lock washer on. Instead, I put a regular washer on. Why? I don’t know. It was in the same bag as the screws I needed for the previous step, so I guess I just assumed. Should have spent an extra three seconds and looked at all the bags a bit more, I guess. Jim, I think you need to put a big orange warning label on the bag, something to the affect of “newly acquired robot parts affect seratonin levels in the brain. SLOW DOWN AND STOP BEING AN IDIOT” would probably be sufficient 
.
So once I finished a leg, I tried to put the servos in. This is where I hit my first serious snag. The servos I ordered (from a different supplier) do not fit in the LynxMotion brackets. Apparently the knuckleheads who designed these so-called “standard” sized servos forgot to measure them. So, now I have eighteen servos that sit about an eighth of an inch above the prongs they are supposed to attach to. That is made even worse when you add in the nut that holds on the bearings. So now my servos sit about 7/32" higher than they should, and I have a gap preventing me from attaching the servos to the brackets. That also means the included LynxMotion screws are too short to mount them (but the servos came with longer ones, so that isn’t too big of a deal). What really concerns me about this, however, is that the C brackets have to bend outward just a bit to accommodate the increased height of these servos. I’m concerned what that will do to the strength of the bracket long-term, and also the accuracy, strength, and durability of the servo itself. I’m betting that I will get premature wear on the gears because of this. Another problem with these servos is that the servo horn has holes that are spaced just a little bit differently than the Hitec ones the brackets are designed for. This means that only 1 of the 4 holes will accept a screw. I’ll either have to find new servo horns, make new ones, or maybe just epoxy the ones that are there now and drill new ones. Compared to the other issues caused by these servos, this is minor, but an issue nonetheless.
I decided to take a shot at assembling the body (I purchased the lexan body kit to save money, and also because it will have a lower center of gravity than the SES body) to make sure that the servos did not cause a problem there as well. Unfortunately, they do, so I’ll also have to find a solution to this little problem. I also noticed what I originally believed to be a missing part, a 3/8" nylon spacer. What I now think happened is that the parts underwent a minor change and the assembly guide does not reflect this, as I measured the spacers (metal) that were included with the kit, and they are equal to the combined length of the spacers described in the assembly guide. However, if Jim still makes the smaller spaces, I will need them to make my servos fit. Also included in the body kit are some small nylon spacers that might just work to make my servos work with the standard servo brackets. Hopefully tomorrow I’ll be able to take a dremel to them and see what I can come up with.
I have not completed assembly yet (obviously), but these are my thoughts so far. I like the kit, the products seem to be great, and the packaging, shipping, and customer service I have received thus far has been superb. I couldn’t ask for anything more. Really. I would suggest to anyone else who is looking to a supplier other than LynxMotion for other parts of their robot (particularly servos) to make ABSOLUTELY SURE that they will fit before purchasing them. I spent several hundred dollars on higher-powered servos, but I am paying for that extra power with convenience of assembly, and possibly longevity of the servos in the long run.
I’ll keep everyone posted as things progress.
Mike
I will be adding to the Servo Erector Set a list of non compatible servos. Right now I know for sure anything made by Bluebird Servos are oversized. I suspect any standard size servo from GWS are also oversized, but I have not tested all of them. I worked with Bluebird for several weeks trying to find a solution, but the language barrier made it impossible. They sent me several of their powerful servos for evaluation and I am not impressed. I imediately connected the 620 (I think) to a servo controller and powered it up. Sent it a command to move, and it went Zip… Click… Whirrrr… Crap! The crap sound was actually made by me. 
So with every hitec servo I have ever used, taking it to the extreme left or right position will result in a humming sound, and some heat being generated, but never damage! The servo self destructed in like a nano second. The servos are strong, but they are not designed strong enough to prevent self destruction if commanded too close to, or beyond their physical limit. My heart goes out to you Mike, because I know the slippery road you are on is likely to cause you more headaches than you may realize. For example depending on how you power up your electronics, it’s a matter of time till the servo controller or whatever electronics you are using will inevitably send out the incorrect pulses and… welll… Zip… Click… Whirrr… x 18. 
Unfortunately the old saying caveat emptor - let the buyer beware, holds true for super powerful, super cheap servos…
As for the missing components. You are correct in assuming the two nylon standoffs were used to make a part as long as the current aluminum part is. You were looking at an older (version 1) of the assembly guide.
lynxmotion.com/images/html/build042.htm
But if you look at the current (version 2) you will see it has been updated.
lynxmotion.com/images/html/build42a.htm
We really try to keep up on that sort of thing. Anyway, good luck with the project!
Jim,
Thanks for the replies, both here and in the numerous e-mails we’ve sent back and forth. You’ve been more than helpful during this entire process, and since long before I ever purchassed anything from you. I really can’t say enough good things about your customer service.
The few minor issues I have had with construction so far are certainly NOT in any way your fault, but you have gone out of your way to help me fix them. For that, I am very grateful.
I have not experimented with my servos much (as discussed via e-mail, they are manufactured by Blue Bird), but I have not yet had the problem you speak of, and I have commanded them past their ranges at full speed. In fact, the first servo I ordered had faulty electronics (I believe), and would sometimes snap to a full clockwise position, and require a reset before it would move again. Eventually, I will be pulling the standard electronics and putting in boards from www.openservo.com, so I was not too upset by this. There should be a thread or two on here from when I was having these problems a few months ago.
Your assembly guides (even though I was reading the wrong one) are great. I should have read it a bit more thoroughly on one or two steps, but all went well. I now have everything assembled (with the exception of the servos, of course), and will post pictures as soon as I can find a solution to my not so standard “standard size” servo problem. Had I known this would be an issue, I never would have bought servos from anyone but you, and I certainly won’t in the future. You and your products have earned all my business from now on.
Mike
Quick status update:
I have three legs fully assembled now. I haven’t had nearly the time I would like to work on it. Midterms are over now, and spring break is only a day away though, so that should change soon. The build process has been slowed down considerably by my oversized servos. I tried several methods before settling on the method I finally decided to go with. That method has taken me a while, because I’ve had ot cut and drill spacers for every servo, as well as modifying the servo cases themselves. Hopefully I’ll have time to finish assembling it tomorrow.
The good news is that I got a new table, and have transferred all my tools and parts to it, and off of my computer desk. For the first time in about a month, I can see my desk again. It’s a nice feeling, and I think I’ll be more productive this way.
I also started putting together a website sometime last week or so, which I will be tracking my progress with. This should be a bit more convenient for me, as it will save me from having to type things twice, and it should also save Jim’s bandwidth, as I intend to post a lot of pictures, code, and anything else that is relevant. I’ll post abstracts here for those of you who don’t have the time (or desire) to read the full posts. I’ve still got a bit of work to do on it before it is ready, so the link won’t be added to my profile for another day or two, if not more.
Mike
So do you have any pictures to post on your progress yet?
Pete
The battery on my camera ran out while I was taking pictures of how to modify a Blue Bird servo to fit the LynxMotion brackets (details available on my website). Unfortunately, that is when I found out my charger no longer worked. A new one is on its way to me now, but will not be here for another week, so I don’t have any pictures of the completed robot yet.
My development diary can be found on my website, mike-winters.com.
I am still having power issues. I know what the problem is (servos draw so much current that the volts drop out), but I have not yet been able to solve it. It has been suggested that I look into using 18 large capacitors, one for each servo, to fix this problem. Anyone have any comments or ideas?
Thanks,
Mike
Well, the power snag has turned into a pretty serious issue. Nothing I have tried is getting all 18 servos to move rapidly in groups, as they will need to do for it to walk.
I am out of ideas at this point. I don’t know very much about electronics (very little, in fact), so I am totally at a loss as to what to do to fix this problem. For development and testing, I need to be able to power them off a wall supply. If my 250W computer PSU (discussed here) won’t cut it, what will?
More importantly, however, I need to ensure that whatever workaround or solution I go with now will also work when I start running this thing off batteries. Currently, the best batts I have been able to find are these. I plan to do as Andy has done, and step them down to 6v/5v. I figure I can fit at least 2, and possibly as many as 3 or 4 of these on my robot. The problem is that I am pretty much broke at this point, having just purchassed the parts for the hex, as well as the servos, so I won’t be able to afford these batteries and the associated charger, etc for at least a few months.
I really need help at this point. I am not a hardware guy, my focus is software. I need to get the hardware issues solved so I can start writing code. I’m out of my element here, and out of ideas. Any help you guys can provide will be greatly appreciated.
Thanks,
Mike
Hello Mike,
i am not sure if you found that thread. there is some discussion about power supplies as well. it might be of help…
However: i am just at the same problem as you: i fused my 5V PSU from an old computer PSU with (4amps, i think) and plan to use this for development. However: i am still waiting for my parts (and servos) to give it a try.
as for autonomous action, i have recently bought a 7.2V 3000mAH NiMH battery pack. hopefully, this is enough…
regards
Yes, I read that thread a while back.
My problem is that I am past the point of thinking/hoping something will work. I have now hit the point where what I have DOES NOT work, and I am about out of ideas on how to fix it. As suggested by someone doing a similar project, I am going to try picking up some 1000uF capacitors today and see if they will be enough to prevent these brownouts from occuring.
Mike
Read your other thread, Mike.
Hey Mike, I’m not sure why you are still having trouble. I routinely control 18 HS-475 servos form a little bitty six cell “AA” NiMH pack. The pack is good for 1600mAh and I can run an EH3-R for over 20 minutes walking continuously. And this is without the separate 9vdc battery for the electronics. There is absolutely no reason you can’t control 18 servos from this battery packs big brother. Our 7.2vdc 2800mAh pack should control those servos with no trouble. If a PC powersupply is not capable of controlling these servos then you have another problem. I suspect wiring. What guage of wire are you using? It has to be 18 or 16 guage to carry the current. Also connections have to be solid. No wire twisted together, or little clip connectors. Think heavy duty here… I sense the frustration in your posts. Send images to me, or the forum showing your setup. We want to help…
Jim,
I’m wishing I had just purchassed it all from you to begin with. You were right when you said those initial problems I had with the Blue Bird servos were just the tip of the iceberg.
I’m using 18ga wire, and the connectors are two pin molex style connectors I purchased from Radio Shack. The wires are crimped and soldered into them.
Unfortunately, my digital camera has a dead battery, and the charger stopped working (power issues are plaguing me, it seems ). I have a new charger on the way, but it won’t be here until the end of the week.
I’m going to try the capacitors later today, and will post my results.
Thanks,
Mike
Edit: Jim, I also don’t know why I’m still having problems. I figured the computer PSU would be plenty. I may look in to getting another supply, in the event that this one is faulty or simply inadequate (it was pretty cheap).
I just did another test. After carefully putting each servo to center one by one, I put it on the table (it was supported during the centering process), and the voltage dropped from ~5.3 to ~4.75v. Lifting one leg dropped it down to ~4.6v (one leg in the air, five on the ground). Trying to lift a second leg caused it to get twitchy again. I wasn’t metering it when it happened, so I don’t know what the drop was, but whatever it was, it was large enough to cause the servos to act up.
I’m off to try to find some capacitors now. We’ll see what I can come up with.
Mike
Mike, are you talking about continuously holding the voltage at 4.6 volts, or just it dipped down to that while the leg was moving? If the voltage is holding steady while under load then it is unlikely the capacitors will entirely solve your problem. They will help with spikes or surges of current by, in effect, buffering it out some but if you are sustaining the 4.6 volts under load the problem is probably not spikes. They might buy you some margin before you start seeing flaky behavior though, particularly if the voltage is dragged down and then you start moving a leg.
Question: Where did you take the voltage measurement? If not AT the pack then is it possible to measure the voltage AT the pack when loaded like this? I am asking to determine if the drop in voltage is from the packs internal resistance or the wiring between the pack and the servos. Also if you could actually measure the current coming from the pack when under this load it may be helpful to know as well. I am looking to see how hard you are drawing off the pack. Be aware this could easily be upwards of 10A with 18 servos under load so don’t pop the fuse in your meter, maybe start by supporting the robot and observe as you place it on its feet, and remember that the current meter will drop a small amount of voltage itself so flaky might happen sooner with it in place.
It was holding pretty steady. Small fluctuations, but only a few millivolts or so.
I measured the voltage directly off wires attached to the molex connector, and observed the same results. Generally, I am measuring off the screws on the SSC-32 terminal, because that is easier, and appears to be yielding the exact same numbers with everything I have tested so far.
I tested the current draw a few days ago under several conditions, and I think the number was about 3.5 amps for 6 servos. The meter did affect the performance, however, as the servos got twitchy at times when doing this, but when the meter was not connected in series to measure the current, the servos perfromed as they should.
I just got back from picking up a few caps, and I am about to wire them up now. Hopefully they help to solve the problem. If not, I don’t know what I am going to do.
Mike
From what I just read the power supply is not working correctly. Capacitors will not help this.
You’re right again, Jim. The capacitors didn’t seem to help, although I only tried a few of them.
After that, I tried a 7.2v 2000mAh battery pack, and it seems to be more along the lines of what I’ll need. With this, the robot was able to stand on 6 legs, then pick 3 up and stand on the other 3, while keeping the 3 hovering legs in motion. The computer PSU could not handle standing on 3 legs with the other 3 in the air.
I did some slow moves (macro walking gait tests) and everything seemed to be working fine. Unfortunately, I think I may have cooked two of the servos. One happened earlier on, the second happened sometime during the move tests, but I am not sure when. I’m about to go to bed, and will have to figure out what the story is on those two servos tomorrow.
So, in addition to all the other problems associated with Blue Bird servos, it seems they are not as tolerant of over volting as HiTecs are. Hopefully tomorrow I will be able to figure out exactly what happened, and possibly even fix it (although I doubt it).
Mike
After ordering two Hitec 645MG servos to replace the cooked BMS servos, I have made another small update to my website, now with pictures of the assembled robot.
I’ll probably be focusing my time in the near future on the control software side of things. I have a lot of work to do on the sequencers and customizeable GUI before that is ready for release and beta testing.
Mike
I checked out your site. I stumbled onto the images of the blue bird servos. The image below I found interesting.
mike-winters.com/Servo%20Photos/BMS%20660MG%20hexagon%20drilled%20close-up.jpg
I’m the reason the hex part was put into the mold. We tried to get a workable solution to the size problem, but they fumbled the servo horn part, and I could never get them to address the self destruct feature of the servos.
