Need advice for building KHR-2hv
Need advice for building KHR-2hv
by triscope
Mon Sep 17, 2007 12:38 am
Hello, my name is Eric and I am looking into building myself a bot such as khr-2hv. The only problem for me right now is the cost involved. I really really want to have one of these but I will have to go down the cheap route. The servo's seem to be the only costly parts in these kits.
I have done research for the best servo's for my budget and have found that the towerpro MG995 are some of the cheapest ones with the best performance (I could find anyway). On paper, they provide better speed and torque than the krs-788hv. I found someone on ebay who is selling 20 of them for 100$ plus shipping. I also plan to buy a 10.8v battery pack.
Now I know you have some experience with these servos and I know they arent the greatest in terms of reliability, however I do need something cheap, and for starters this would be fine for me. I am very handy and can fix many things, so if something breaks, hopefully ill be able to fix it or modify it slightly.
And finally, I would like to know if it would be possible to purchase the khr-2hv (or khr-1) kit wihtout the servos or battery pack. Also will RCB-3J board be able to work properly with these servos? The standard KRS-788HV motors run at like 10v correct? Will I have to modify the supply voltage? And also is the mounting for the mg995 compatible with the KHR brackets or will I have to modify?
Anyways, im looking at building this robot at under 400$ for my budget. If I could find the kit without the servos and battery, that should cut down the costs quite significantly right?
So let me know what you guys think, I would greatly appreciate any of your advice and opinions. Thank you so much for your time.
Eric
I have done research for the best servo's for my budget and have found that the towerpro MG995 are some of the cheapest ones with the best performance (I could find anyway). On paper, they provide better speed and torque than the krs-788hv. I found someone on ebay who is selling 20 of them for 100$ plus shipping. I also plan to buy a 10.8v battery pack.
Now I know you have some experience with these servos and I know they arent the greatest in terms of reliability, however I do need something cheap, and for starters this would be fine for me. I am very handy and can fix many things, so if something breaks, hopefully ill be able to fix it or modify it slightly.
And finally, I would like to know if it would be possible to purchase the khr-2hv (or khr-1) kit wihtout the servos or battery pack. Also will RCB-3J board be able to work properly with these servos? The standard KRS-788HV motors run at like 10v correct? Will I have to modify the supply voltage? And also is the mounting for the mg995 compatible with the KHR brackets or will I have to modify?
Anyways, im looking at building this robot at under 400$ for my budget. If I could find the kit without the servos and battery, that should cut down the costs quite significantly right?
So let me know what you guys think, I would greatly appreciate any of your advice and opinions. Thank you so much for your time.
Eric
by AI-Bot
Mon Sep 17, 2007 8:07 am
Hi Eric
What ever you do, don't buy MG995.
25% of the servo I get are broken before I even get the change to use it.
There is NO QC for any of those servo.
The one that works, they are noisy, weak...(don't trust the spec) and they tend to vibrate alot, and can't get back to proper neutral positiion.
Trust me 788 is alot stronger than the MG.
(don't belive the spec they give to you)
MG only 6V, but you can push to 7.2.
But if you push to 10.8V, I believe you will get smoke coming out of them wihin a few mintues... The curcuit of MG was designed for only 6V they are not HV servo.
You are better off with Hitec MG 645. I know they cost a bit $30 each, but you are better off.
You can buy RCB3J separately for $400.
But if you are going to use MG or Hitec servo with RCB3J, make sure your power source input is no more than 7.2V. Otherwise you will burn your servo.
Make sure you power source can handle at least 1.5 A.
If you are trying to build a humnoid $400, I sugggest you use different micro servo controller, because RCB3J cost too much already.
You can get different board for under $100 which is easier to program.
$100 micro servo controller.
$100 for metals...
$150 for servo
$50 misc.
It is going to be hard to get 20 servo for under $150.
To be honest with you... I think you are better off with Hitec 475 than TowerPro servo.
I hope that help.
If you have any more questions, you can PM or post it here, I am sure a lot of people here can help you.
What ever you do, don't buy MG995.
25% of the servo I get are broken before I even get the change to use it.
There is NO QC for any of those servo.
The one that works, they are noisy, weak...(don't trust the spec) and they tend to vibrate alot, and can't get back to proper neutral positiion.
Trust me 788 is alot stronger than the MG.
(don't belive the spec they give to you)
MG only 6V, but you can push to 7.2.
But if you push to 10.8V, I believe you will get smoke coming out of them wihin a few mintues... The curcuit of MG was designed for only 6V they are not HV servo.
You are better off with Hitec MG 645. I know they cost a bit $30 each, but you are better off.
You can buy RCB3J separately for $400.
But if you are going to use MG or Hitec servo with RCB3J, make sure your power source input is no more than 7.2V. Otherwise you will burn your servo.
Make sure you power source can handle at least 1.5 A.
If you are trying to build a humnoid $400, I sugggest you use different micro servo controller, because RCB3J cost too much already.
You can get different board for under $100 which is easier to program.
$100 micro servo controller.
$100 for metals...
$150 for servo
$50 misc.
It is going to be hard to get 20 servo for under $150.
To be honest with you... I think you are better off with Hitec 475 than TowerPro servo.
I hope that help.
If you have any more questions, you can PM or post it here, I am sure a lot of people here can help you.
by Robo1
Mon Sep 17, 2007 10:24 am
Have a look over at openservo.com There have a lot of info on cheap digital servos.
As far a the brackets go you can buy them on there own. I would go for the khr-1 brackets as there better quality and metal. If I was you get some brackets and cheap servos 2-3 and get a decent controller for them the RCB isn't that good and will only properly work with KONDO servo's. Have a look on the WWW for servo control boards or go gumstix and digital servo's.
Just my 50 cent.
Bren
As far a the brackets go you can buy them on there own. I would go for the khr-1 brackets as there better quality and metal. If I was you get some brackets and cheap servos 2-3 and get a decent controller for them the RCB isn't that good and will only properly work with KONDO servo's. Have a look on the WWW for servo control boards or go gumstix and digital servo's.
Just my 50 cent.
Bren
by Ray
Mon Sep 17, 2007 2:33 pm
Hi Eric,
perhap the following points would support why you are better use RBS788HV
1) The Body frame is designed using the dimension of 788HV and the
servo arm is designed for the insertion of the servo head of RBS 788HV
if you use other servos, you may need to re-design or re-work the
body frame.
2) RCB3J provide power of 11V, It will burn 6V servos unless you provided
a suitable high power supply to it. (may be around 10W)
3) No more Teaching function you can use.
4) Usually, Servo not designed for Robot only have rotation angle of
120 degree, it limit your motion.
(you may rework your servo if you can change the resistor value)
5) RCB3J cannot make suitable compensation and linearity for your
unknow servo and many important servo characteristic variable cannot
be done for say, changing high torque with low or high speed, stiffness etc.
6) You need to make the free horm portion at the other side of the servo in order to make the axle complete. you should rework you servo using, say a screw, nut, as well as drilling.
Believe me, unless you are a experienced robot hobby, you cannot easily get a satisfactory result.
I suggest you to buy a 2nd hand KHR2HV, once, you got used to it, you may know more.
Ray.
perhap the following points would support why you are better use RBS788HV
1) The Body frame is designed using the dimension of 788HV and the
servo arm is designed for the insertion of the servo head of RBS 788HV
if you use other servos, you may need to re-design or re-work the
body frame.
2) RCB3J provide power of 11V, It will burn 6V servos unless you provided
a suitable high power supply to it. (may be around 10W)
3) No more Teaching function you can use.
4) Usually, Servo not designed for Robot only have rotation angle of
120 degree, it limit your motion.
(you may rework your servo if you can change the resistor value)
5) RCB3J cannot make suitable compensation and linearity for your
unknow servo and many important servo characteristic variable cannot
be done for say, changing high torque with low or high speed, stiffness etc.
6) You need to make the free horm portion at the other side of the servo in order to make the axle complete. you should rework you servo using, say a screw, nut, as well as drilling.
Believe me, unless you are a experienced robot hobby, you cannot easily get a satisfactory result.
I suggest you to buy a 2nd hand KHR2HV, once, you got used to it, you may know more.
Ray.
by triscope
Mon Sep 17, 2007 11:21 pm
Thanks for all the great input guys!
So from what I'm reading my situation seems kinda bleak.
Heres what I came up with so far. I can find a MR-C3024 control board (same one that was used in robonova) for about 240$ instead of 400+ with the rcb3. Btw it was nearly impossible to find rcb3 boards for sale. So MR-C3024 are much more popular and work on 6-7.4V output, so it would work great with regular servos. It also has 24 outputs, and 64k memory atmel chip.
I tried looking some more, for cheap servo's and couldnt really find anything decent for under 10$. I found these other towerpro SG-5010 (i know lol) http://www.nitroplanes.com/41ghitoporac.html
They provide less torque than the mg995 but are slightly quicker however they have plastic gears and not metal (more prone to failure and breaking?)
And as for the body and metal brackets, i will have to find a place that sells all the brackets for khr-1 or 2hv for like 200$ or so.
But anyways, I can understand how awfull these towerpro motors are, but for 100$ for 20 servos, how can you beat that. I found nothing on the market for high performance servos under 10$ a peice. But lets just say I were to order these and rework and modify most of them. Would I have any chance of fixing or making the amp inside the servo more stable? I always beleive in the old saying, when theres a will, theres a way. However if you guys think I have absolutely no chance in hell with my plan and I will fail miserably, please let me know
I wont get my feelings hurt and it would allow me to not spend so much cash for nothing. Im poor, and I need to find a way to build this thing as cheaply as possible. I mean the khr series and other bots sell for about 1000$, how hard would it be to cut the costs in half? I know its not going to be easy, but im up for a challenge 
Thanks a lot guys for all your help!
Eric
So from what I'm reading my situation seems kinda bleak.
Heres what I came up with so far. I can find a MR-C3024 control board (same one that was used in robonova) for about 240$ instead of 400+ with the rcb3. Btw it was nearly impossible to find rcb3 boards for sale. So MR-C3024 are much more popular and work on 6-7.4V output, so it would work great with regular servos. It also has 24 outputs, and 64k memory atmel chip.
I tried looking some more, for cheap servo's and couldnt really find anything decent for under 10$. I found these other towerpro SG-5010 (i know lol) http://www.nitroplanes.com/41ghitoporac.html
They provide less torque than the mg995 but are slightly quicker however they have plastic gears and not metal (more prone to failure and breaking?)
And as for the body and metal brackets, i will have to find a place that sells all the brackets for khr-1 or 2hv for like 200$ or so.
But anyways, I can understand how awfull these towerpro motors are, but for 100$ for 20 servos, how can you beat that. I found nothing on the market for high performance servos under 10$ a peice. But lets just say I were to order these and rework and modify most of them. Would I have any chance of fixing or making the amp inside the servo more stable? I always beleive in the old saying, when theres a will, theres a way. However if you guys think I have absolutely no chance in hell with my plan and I will fail miserably, please let me know
I wont get my feelings hurt and it would allow me to not spend so much cash for nothing. Im poor, and I need to find a way to build this thing as cheaply as possible. I mean the khr series and other bots sell for about 1000$, how hard would it be to cut the costs in half? I know its not going to be easy, but im up for a challenge
Thanks a lot guys for all your help!
Eric
by triscope
Tue Sep 18, 2007 2:17 am
hey I just found this controler: Lynxmotion SSC-32 Servo Controller
http://www.robotshop.ca/home/suppliers/ ... oller.html
Is it a good deal for 50$?? or should i just go with the more expensive mr-3024?
http://www.robotshop.ca/home/suppliers/ ... oller.html
Is it a good deal for 50$?? or should i just go with the more expensive mr-3024?
by Robo1
Tue Sep 18, 2007 8:36 am
The SSC-32 is a go board. Some people here have changed the board in there KHR-2 to this board so some might say that it's better then the RCB. Have a look at this openservo this thread has some good input about cheap servo's.
You can get all the brackets from robosavvy. have a look at This. I'm in the process of replacing all the plastic brackets with these metal one's.
My advise would be get the controller and some servo's 2-4 and some brackets and have a play. You don't want to buy 20 servo's realise the crap then have to buy new one. it would make more sense to buy a couple and work from there. Also note that different servo's will take different forces. So expensive ones for the legs and you can get away with cheap ones for the arms.
Bren
You can get all the brackets from robosavvy. have a look at This. I'm in the process of replacing all the plastic brackets with these metal one's.
My advise would be get the controller and some servo's 2-4 and some brackets and have a play. You don't want to buy 20 servo's realise the crap then have to buy new one. it would make more sense to buy a couple and work from there. Also note that different servo's will take different forces. So expensive ones for the legs and you can get away with cheap ones for the arms.
Bren
by triscope
Tue Sep 18, 2007 11:04 pm
Ok, I read up on the ssc32 and it really looks like a good simple board that is very flexible. I already have 24lc256 eeprom chips at home in case of future upgrades, i already have all the rs232 serial cables.
I can buy those mg995's from united hobies for 150$(16 of them) including shipping http://www.unitedhobbies.com./UNITEDHOB ... dProduct=2
I found some people who acctually modified and played with these servos to perform acceptably. First they removed the casing and cleaned all the metal gears, then applied certain capacitance on the motor and the pots (something like 30ųf or something) and got them to work great. without too much overshoot and problems centering and the reseting issues.
I can get a 7.2v NiMH (6 cell ) 2600mAh so it should give more than enough power to the ic and servos to last a long time. I think it will fit...
http://cgi.ebay.com/7-2V-2600mA-BATTERY ... dZViewItem
So in total I have 150$ for the servo's, 40$ for the controler, 35$ for the battery, so that leaves me 175$ for all the backets screws and mounting plates. Can anyone help me with a round up of all the needed mounting accessories? I looked on the link you gave me and I can only find a few parts that I need.
What do you guys think so far. Am I an idiot for doing this? Or do you think it might be a good idea?
I can buy those mg995's from united hobies for 150$(16 of them) including shipping http://www.unitedhobbies.com./UNITEDHOB ... dProduct=2
I found some people who acctually modified and played with these servos to perform acceptably. First they removed the casing and cleaned all the metal gears, then applied certain capacitance on the motor and the pots (something like 30ųf or something) and got them to work great. without too much overshoot and problems centering and the reseting issues.
I can get a 7.2v NiMH (6 cell ) 2600mAh so it should give more than enough power to the ic and servos to last a long time. I think it will fit...
http://cgi.ebay.com/7-2V-2600mA-BATTERY ... dZViewItem
So in total I have 150$ for the servo's, 40$ for the controler, 35$ for the battery, so that leaves me 175$ for all the backets screws and mounting plates. Can anyone help me with a round up of all the needed mounting accessories? I looked on the link you gave me and I can only find a few parts that I need.
What do you guys think so far. Am I an idiot for doing this? Or do you think it might be a good idea?
by Robo1
Wed Sep 19, 2007 5:15 pm
I thin it's not a bad idea. I still think that you should buy a couple of servo's and test them out before you get 16. the battery will give you a longer life but will weigh more so I normally have a small 1000 mha battery and hook it up to a power supply most of the time. When people come around them you can just use the battery.
The Brackets. You need two feet platesand the side pieces couldn't see them n this site but have a look around and the arm brackets that are the same as the leg peices that are Here
If you look at the bottom of the last link theres also the free horn and the servo horns that go with the brackets.
Bren
The Brackets. You need two feet platesand the side pieces couldn't see them n this site but have a look around and the arm brackets that are the same as the leg peices that are Here
If you look at the bottom of the last link theres also the free horn and the servo horns that go with the brackets.
Bren
by triscope
Wed Sep 19, 2007 8:40 pm
Ok so I compiled a list of parts that I would need from this site's store. I didnt find everything. Btw how many servo arms do I need?? Because on the site they sell them for 15$ a pair, but I think I need like 14 pairs of these. That would cost me 200$ just in servo arms. Thats a bit rediculous. Is there no way to order all the brackets as a kit?? And btw what is the difference between the free hone and the servo hone. Do I need both?
hands 14.49
top cover 14.49
body frame 24.15
frame unit 38.64
Servo bracket B 14.49
Servo arm 14.49
foot unit 19.32
servo bracket C 14.49
Foot sole 14.49
Servo horn(x12) 14.49
Board Cover 33.81
screws 3.87
Arm support 5.79
total 227$USD
I know im missing stuff, but I just dont know where to find the rest of it. Any ideas??
edit: btw those were all KHR-1 parts. Is there a big difference between those and the khr-2hv? And which are better?
hands 14.49
top cover 14.49
body frame 24.15
frame unit 38.64
Servo bracket B 14.49
Servo arm 14.49
foot unit 19.32
servo bracket C 14.49
Foot sole 14.49
Servo horn(x12) 14.49
Board Cover 33.81
screws 3.87
Arm support 5.79
total 227$USD
I know im missing stuff, but I just dont know where to find the rest of it. Any ideas??
edit: btw those were all KHR-1 parts. Is there a big difference between those and the khr-2hv? And which are better?
by tempusmaster
Thu Sep 20, 2007 9:13 am
triscope wrote:Ok so I compiled a list of parts that I would need from this site's store. I didnt find everything. Btw how many servo arms do I need?? Because on the site they sell them for 15$ a pair, but I think I need like 14 pairs of these. That would cost me 200$ just in servo arms. Thats a bit rediculous. Is there no way to order all the brackets as a kit?? And btw what is the difference between the free hone and the servo hone. Do I need both?
hands 14.49
top cover 14.49
body frame 24.15
frame unit 38.64
Servo bracket B 14.49
Servo arm 14.49
foot unit 19.32
servo bracket C 14.49
Foot sole 14.49
Servo horn(x12) 14.49
Board Cover 33.81
screws 3.87
Arm support 5.79
total 227$USD
I know im missing stuff, but I just dont know where to find the rest of it. Any ideas??
edit: btw those were all KHR-1 parts. Is there a big difference between those and the khr-2hv? And which are better?
Before you go too far down the KHR-1 path, you should send a PM to Limor and find out if the parts are still available. The original KHR-1 is being phased out, and some people on this forum have reported not being able to locate some older parts they wanted.
Yes, there is a difference between the servo and free horns. Studying the photos in the manuals should give you a good idea of how they differ. It's important, especially if you plan to modify/hack your design at all.
As Robo1 mentioned, some of the KHR-2 brackets are plastic, and like most plastic parts, they will break if overstressed. Sometimes the builder puts too much torque on the locking screw and compresses the plastic which causes internal stresses and potential cracks. The locking screw is only intended to keep the two mating parts in place, so torquing it down on it doesn't make it any more secure, but can contribute to problems.
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by limor
Sat Sep 22, 2007 4:37 pm
The parts we advertise at our online store are still in production.
Sometimes it will take a few weeks to de-list a part that has been phased out by Kondo. If a part is not available at our UK warehouse, it can be sourced from Japan.
send an email to sales@robosavvy.com with the list of parts you are interested in.
Sometimes it will take a few weeks to de-list a part that has been phased out by Kondo. If a part is not available at our UK warehouse, it can be sourced from Japan.
send an email to sales@robosavvy.com with the list of parts you are interested in.
by limor
Sat Sep 22, 2007 4:41 pm
btw: you can see the full content of the store on a single xml page.
http://robosavvy.com/store/feeds/edgeio_feed.xml
this is experimental and in the future it will look prettier (evenly sized images prices, add-to-cart buttons..)
http://robosavvy.com/store/feeds/edgeio_feed.xml
this is experimental and in the future it will look prettier (evenly sized images prices, add-to-cart buttons..)
by RoBotX
Wed Oct 24, 2007 7:45 pm
SO how is it going with this project? I'm interested in doing something similar and the big question is: the servos from unitedhobbies work or not? If not, please describe the problems. I am also considering getting these servos: http://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=2 or these: http://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=3743
Thank you verry much.
Thank you verry much.