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matterest
01-23-2010, 03:56 PM
do i need to get the hs 645 servo upgrade or is there an alternitive

Nishi
01-23-2010, 04:04 PM
what do you mean by alternative?.. You don't need to get the upgrade at all in my opinion. Not until you know you need them.

matterest
01-23-2010, 04:07 PM
even with camera gun and battery

Nishi
01-23-2010, 04:11 PM
then yeah I expect you would, and I'm even more convinced a bunch of other people are about to shut me down even further and say you definitely do. If you want a build a complete fighting mech buy the best Servos you can. You'll get what you pay for.

lnxfergy
01-23-2010, 04:20 PM
I'm not sure anyone can say you *need* the 645s, and there are certainly those of the opinion that you don't.

Personally, I'd rather have more power than I need -- than have less power than I need -- in the first case, you can be bit more sloppy about payload, in the second case, you'll be buying new servos.

-Fergs

matterest
01-23-2010, 05:28 PM
yeah but will it be able to walk at all you think?!?

MikeG
01-23-2010, 05:58 PM
Considering the leg segments are fixed and your payload is known (to you only), you should be able to estimate the minimum joint torque required for your project.

matterest
01-23-2010, 06:26 PM
Considering the leg segments are fixed and your payload is known (to you only), you should be able to estimate the minimum joint torque required for your project.


my robot hasnt come in yet though and when it does how can i calculate this?!?:confused::confused::confused::confused::co nfused::confused::confused::confused::confused::co nfused::veryhappy::veryhappy::veryhappy:

zoomkat
01-23-2010, 07:06 PM
If you have already ordered your brat with the standard servos, then why don't you put it together and load it with your added weight and see how well it works? I think there may be examples on the lynxmotion board (if this is the "brat" you are talking about) that have guns and stuff on them. Look and see what they use.

matterest
01-23-2010, 07:56 PM
yeah but i am still waiting for it to arrive

matterest
01-23-2010, 08:06 PM
ok this is what i am trying to do http://www.lynxmotion.com/images/html/build156.htm
do i need those servos ? i didnt see anything!

MikeG
01-23-2010, 08:26 PM
Torque is Force * Distance; ft-lbs, oz-in, kg-cm... Motor manufacturers display this specification so folks can determine if the motor will fit their needs.

Consider a 10cm wrench and a bolt. When a 1kg force (@90 degrees) is applied to the wrench handle the bolt feels (moment) 10cm * 1kg of twisting force or 10 cm.kg. If the wrench is 5 cm long and you want the same torque applied to the bolt, you must apply 2kg of force. ie. 5 cm * 2kg = 10 kg.cm.

The HS-645 specs is 9.6 kg.cm.

lnxfergy
01-23-2010, 08:31 PM
I believe most of the Brat-Mechs are using 645s. Whether you *need* them, I'm not sure, but I'm pretty certain performance would be better with the 645s. You might ask in the Lynxmotion forums, as the Brat-Mech users are more active over there, and only visit TRC every so often.

-Fergs

lnxfergy
01-23-2010, 08:33 PM
Torque is Force * Distance; ft-lbs, oz-in, kg-cm... Motor manufacturers display this specification so folks can determine if the motor will fit their needs.

Consider a 10cm wrench and a bolt. When a 1kg force (@90 degrees) is applied to the wrench handle the bolt feels (moment) 10cm * 1kg of twisting force or 10 cm.kg. If the wrench is 5 cm long and you want the same torque applied to the bolt, you must apply 2kg of force. ie. 5 cm * 2kg = 10 kg.cm.

The HS-645 specs is 9.6 kg.cm.

Mike, I'm pretty certain the original video of the Brat-Mech used HS-475s, so it's not that they are completely overloaded on torque... I think the bigger question is how much of a safety margin is needed -- in other words, how close can we get to max torque usage before performance degrades. Either way, easiest solution for the OP is to ask Lynxmotion, they've done testing with the 475s and the 645s and should be able to give an answer.

-Fergs

EDIT: I did do a quick search of the lynx forums, but can't seem to find any definitive answer that warns users to steer clear of 475/485 servos. However, they are recommending a 645 for the turret pan servo, which makes me think the legs should be at least 645s as well....

MikeG
01-23-2010, 08:45 PM
lnxfergy, I'm getting a little more grouchy as the years go on... and these kind of questions... well

The point I was trying to make... do your homework and make an educated decision.

Nishi
01-23-2010, 09:44 PM
if you ordered as is then your getting 422's which really are a minimum and are described to "work well" with a minimum payload. I'd do what someone else has said and wait to see in practice whether or not you personally require more power, if your hoping to compete in some kind of tech ware for I expect you may with final payload.

;)

Robot Dude
01-25-2010, 02:08 PM
Yeah most BRAT builders for Mech Warfare are using 645 servos. Although I did see a youtube video of a BRAT based Mech sporting guns and using 422 servos! It's actually walking around and everything. lol


http://www.youtube.com/watch?v=mqpRSWYTyc4

Nishi
01-26-2010, 12:02 AM
Thing stands on one leg for a while too, it is impressive.. @RobotDude My Brat Arrives today via UPS.. Woooo!

4mem8
01-26-2010, 12:37 AM
Personally i would use 645's on the brat, but that is just me. My scout ed209 has HSR 5990ST's but that is a different mech and designed for higher loads.

matterest
01-26-2010, 02:25 PM
Yeah most BRAT builders for Mech Warfare are using 645 servos. Although I did see a youtube video of a BRAT based Mech sporting guns and using 422 servos! It's actually walking around and everything. lol


http://www.youtube.com/watch?v=mqpRSWYTyc4

Ok are you sure those are hs 422 servos

DresnerRobotics
01-26-2010, 05:00 PM
Ok are you sure those are hs 422 servos

I would highly suggest that you slow down a bit and wait until you actually receive your BRAT kit. Follow the very detailed build instructions on Lynxmotion's site and get it built, and get it walking via the sample demos. This will teach you a considerable amount about how the robot works.

Next, you can follow their BRAT Mech tutorial (also very detailed) and use that as a guide towards building a Mech, if you so choose.

Your BRAT Mech may very depending upon what you put on it and/or how you build it. HS-422s might work for you, or you might need to upgrade to HS-645s. This is all part of the learning process, and part of learning robotics.

A lot of your answers can easily be answered with a combination of you actually going through the process of building the robot, and doing your own research/homework on things as you go. One step at a time. :)

Robot Dude
01-27-2010, 12:00 PM
Ok are you sure those are hs 422 servos

In this post on my forum. http://www.lynxmotion.net/viewtopic.php?p=58031#p58031

He announces the release of this video. He states he plans to upgrade to 645 but has not done so yet.


http://www.youtube.com/watch?v=mbeW3TmTxP0

But later he posted this video stating it was fully configured. So This last video may in fact be using 645 servos. Sorry for the assumption. Really need to here back from robonoob to know for sure.


http://www.youtube.com/watch?v=mqpRSWYTyc4

This just may be a good illustration of the difference between 422 and 645 servos. lol ;)

RandomFish
01-27-2010, 07:33 PM
The second you have a bot, you want better servos, always keep that in mind when making purchases. The second you have better servos you better ones. The fun thing is once you've gone through this cycle a few times you have a lot of leftover servos to start another project. And I've always felt fine running 422s at 7.2v(and know a few other people who frequently do) and haven't lost any. They are however the only servos that I even consider doing this too and for my own sake I don't recommend this.

Nishi
01-27-2010, 09:07 PM
The second you have a bot, you want better servos, always keep that in mind when making purchases. The second you have better servos you better ones. The fun thing is once you've gone through this cycle a few times you have a lot of leftover servos to start another project. And I've always felt fine running 422s at 7.2v(and know a few other people who frequently do) and haven't lost any. They are however the only servos that I even consider doing this too and for my own sake I don't recommend this.

Pardon me RandomFish, but that's interesting can you elaborate on why you wouldn't run 7.2 through say a 645, what damage is caused and why?

Also has anyone else noticed the original guy hasn't commented for a while.

DresnerRobotics
01-28-2010, 09:20 AM
Pardon me RandomFish, but that's interesting can you elaborate on why you wouldn't run 7.2 through say a 645, what damage is caused and why?

Also has anyone else noticed the original guy hasn't commented for a while.

I found that 645s get a bit (sometimes to the point of seizures) twitchy at 7.2v, though I haven't blown any out in my testing. I've heard of a few people running 422s at 7.2 with success though. That said: It will void your warranty, proceed at your own risk, etc.

And hopefully the OP has taken my advice and is currently building away and learning from hands on experience :p

RandomFish
01-28-2010, 12:05 PM
645s are only rated to handle up to 6v, while this is also true of the 422s it really isn't worth the risk with anything more expensive unless you"re forking out money for 5980s or 5990s which are made to handle 7.2v. As a general rule of thumb, save yourself money, don't push the envelope.

Noog
01-28-2010, 01:34 PM
As a general rule of thumb, save yourself money, don't push the envelope.

While there is wisdom behind those words, I do have to ask where your sense of adventure went?!

=)

Noog

Nishi
01-28-2010, 03:51 PM
In his defence he did say "general" rule. :o

That's great explanation tho thank you Fish and Tye :)

Robot Dude
01-29-2010, 02:16 PM
I'm one of those guys who uses 422's with 7.2vdc. I don't know why, but they so seam to handle the voltage in stride. The 645 on the other hand does get a bit on the jittery side at 7.2vdc.