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Old Nov 20, 2012, 07:50 AM
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Hi, everyone
I have been following this thread for quite a while and Ive got to thank everyone for all information provided.
I ordered the UG-1 basic kit to build my own aluminium frame gimbal. Im right now in the proccess of gathering all components together. I shall use a heavy camera -5d mkII- on the gimbal (I know Ill have to build a new board for the camera since that from the kit is designed for smaller cameras)
Ive got a question:
Is there any special reason why a 2.81 ratio should be used in your projects instead of a 4 ratio ( 4:1) -in the way cinestar or photohigher are doing ?. Is it just this 4:1 reduction is aimed to heavier payloads-cameras?
I really appreciate your help
regards
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Old Nov 20, 2012, 11:26 AM
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Quote:
Originally Posted by jmhz View Post
Hi, everyone
I have been following this thread for quite a while and Ive got to thank everyone for all information provided.
I ordered the UG-1 basic kit to build my own aluminium frame gimbal. Im right now in the proccess of gathering all components together. I shall use a heavy camera -5d mkII- on the gimbal (I know Ill have to build a new board for the camera since that from the kit is designed for smaller cameras)
Ive got a question:
Is there any special reason why a 2.81 ratio should be used in your projects instead of a 4 ratio ( 4:1) -in the way cinestar or photohigher are doing ?. Is it just this 4:1 reduction is aimed to heavier payloads-cameras?
I really appreciate your help
regards
You lose travel volume from the servos when you use a high ratio. So the 2.8 to 1 is just a compromise like everything else in life.

Using an external pot is not the cure all. It is a good compromise to get some travel volume back from the servo but you also lose resolution and speed.

Cinestar is using 4 to 1 because they use a very fast lower torque servo. If you plan to use a heavy camera you may consider the Cinestar route. You can buy the 4 to 1 ratio belt and pulleys. Please noticed that Cinestar uses a very light weight large pulley.
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Old Nov 20, 2012, 11:32 AM
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Originally Posted by SeismicCWave View Post
>>If the MI pot is just an analog signal, you could remove it, and wire in an external pot as normal. Of course now you lose all the benefits of MI, and the question becomes, why didn't you just buy this instead?

http://www.hobbyking.com/hobbyking/s...dProduct=22611<<

....because you said it is pretty "rough".
Good point. But the thing is, we have not yet established if the performance of that servos is considered "normal" for most servos, and maybe it's just the brushed MI's that are really good.

Or if it is low performance, is it because of the pot, or the BLS motor? Or is it due to the gearing?

I got a PM from a guy who bought one of the $80 HV MI BLS servos, and he says that it is notchy when it moves. So maybe it's the BLS motor. Or maybe he got a slow one.

I guess we're sort of stuck, because HK does not sell a Lontair servo with a real pot, but brushed motor. If I had some extra money, I'd order a normal pot, HV BLS servo that is fast (maybe the 0.06 sec one) and see if it's smoother.

The problem is we have a lot of permutations:

MI or Pot
High Gearing or Low
BLS or Brushed

I haven't figured it out yet. I just know that the 0.03 sec HV MI servo is butter smooth, and the 0.10 ones are pretty good too. I definitely thing you could use the 0.03 servo in a direct application with no jitter.

Then I have the 0.20 sec HV BLS servo, which is not smooth.

Really need to investigate taking the MI "pot" out of a HV MI Brushed servo. That could work very well.
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Old Nov 20, 2012, 11:55 AM
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>>Or if it is low performance, is it because of the pot, or the BLS motor? Or is it due to the gearing?

I got a PM from a guy who bought one of the $80 HV MI BLS servos, and he says that it is notchy when it moves. So maybe it's the BLS motor. Or maybe he got a slow one.<<

We don't know if it feels and sounds notchy on the bench or in the air. I tested the 70460 MIBL and it does sound more loud and not smooth but I need to put it up in the air and try.
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Old Nov 20, 2012, 12:08 PM
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Well, if in a belted application, it works well in the air, then I'm back to my original question, why not use the non-MI, BLS HV servo if you're going external pot?
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Old Nov 20, 2012, 02:49 PM
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OK guys, I took my MIBL servo apart.
On the board there's a chip about 7x7mm.
Above that is the magnet and is secured to the top cover with a screw so it wont touch the chip.

When I turn the magnet by hand and let go it comes back to spot where the magnetic force keeps it there. In another words if I try to center the servo I have to use some CA to keep it there, if I let go it will swing back to that spot.

The output gear does not have a stopper like the other servos do, I took the pot off and the servo spins 360.

I just wanted to see if it will work. It will as a 360 servo but not with external pot
unless R_Lebervre has some ideas to throw my way.


Just wanted to throw that your way.

Cheers


PS here's a photo from the Lntair website and I circled the pot and the magnet.
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Old Nov 20, 2012, 04:12 PM
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How many wires do you have going from the "pot" to the main control board? Mine only had 3. You could simply extend those wires, and move the whole thing external.
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Old Nov 20, 2012, 07:24 PM
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Quote:
Originally Posted by bcollydas View Post
OK guys, I took my MIBL servo apart.
On the board there's a chip about 7x7mm.
Above that is the magnet and is secured to the top cover with a screw so it wont touch the chip.

When I turn the magnet by hand and let go it comes back to spot where the magnetic force keeps it there. In another words if I try to center the servo I have to use some CA to keep it there, if I let go it will swing back to that spot.

The output gear does not have a stopper like the other servos do, I took the pot off and the servo spins 360.

I just wanted to see if it will work. It will as a 360 servo but not with external pot
unless R_Lebervre has some ideas to throw my way.


Just wanted to throw that your way.

Cheers


PS here's a photo from the Lntair website and I circled the pot and the magnet.
Is yours like the picture? Can the entire MI assembly be removed from the servo by unplugging the six pin connector?
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Old Nov 20, 2012, 08:04 PM
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Quote:
Originally Posted by R_Lefebvre View Post
How many wires do you have going from the "pot" to the main control board? Mine only had 3. You could simply extend those wires, and move the whole thing external.
You can't, the chip is SMD to the board. I didn't pay too much attention but I think the chip has 10 legs 5 on each side. No three wires


Quote:
Is yours like the picture? Can the entire MI assembly be removed from the servo by unplugging the six pin connector?
No, the MI chip is soldered to the board, I wont dare try to take it off

Look at these pics. The MI so they call is only a round magnet about 8mm on a shaft, then themagnet gets attached to the board on top of the chip.

Also the BL Motor has alot more pins to connect to the board.


Tomorrow I will take mine apart again and take a closer look at it and report.

Cheers
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Old Nov 20, 2012, 08:31 PM
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They must have changed the design. Look at the picture I posted a few weeks ago:



And now in fact I can confirm they have changed the design. I bought a bunch of the 47 series last year, including the HK47291TM. I am using 3 of those on the swashplate of my 600 heli. Anyway, one of those if sounding a bit crunchy after a number of crashes (no fault of the servo, it's taken quite a few hits). So I decided to replace it. I ordered another one, same thing HK47291TM. It arrived today, and it is different. The case is not the same as the originals, it has the new case with the two screws on top. It's a very attractive servo.

The performance, just based on the "feel" on the bench is the same as the older ones. The ultra fast one I have on the tail, the HK47902TM, if I rated it an A+ for how it feels on the bench, I'd give the 47291 an A or A-. Compare to the HK84601 which is the BLS Pot servo, which I grade as a B-.

For a little objective data, the deadband on the 47291 appears to be 5uS. The 84601 is 6uS. The 47902 is an amazing 2uS, maybe even 1. I also have a 47179 which is a 0.06 sec servo, and it's 2uS.

But really, none of them can compare with the 47902. It is SO smooth.
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Old Nov 20, 2012, 08:48 PM
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I just opened up the HK84601.

These new servos from Lontair are really very, very good. Features I notice:

- 2 screws on top reinforce geartrain
- non-output gear axles ride in drilled bronze bushings molded into the case
- completely O-ring sealed. The output shaft, top and bottom covers, and even the main 4 screws.
- confirm the BLS motor is not just 3 wires, there are something like 8, so it must be sensored.
- aluminum block is nicely made, as are the new top and bottom covers.
- visible solder quality is not the best. I can't say it's bad, but I've seen better
- almost the entire circuit board is epoxy potted. It's probably quite water resistant, and very vibration resistant.
- bottom cover has a patch of 2-sided foam tape. This makes it hard to disassemble. Also helps vibration resistance.
- motor appears to be glued in, pot is inaccessible. I don't think you can 360 mod these. On the other hand, nothing can move. Very vibration resistant overall.



So, not mod-able, sorry guys. But they're excellent servos for the price. Well, I think they're excellent at any price.

I really really want to try a 47902 on a direct drive camera gimbal. I'd also really like to see a video of one of the fast HV MI BLS servos on a servo tester, just to get an idea what it "feels" like.
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Old Nov 20, 2012, 08:57 PM
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Originally Posted by R_Lefebvre View Post
Well, if in a belted application, it works well in the air, then I'm back to my original question, why not use the non-MI, BLS HV servo if you're going external pot?
Absolutely no reason. However I am not planning to use it on tilt with an external pot though.
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Old Nov 20, 2012, 09:06 PM
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Yeah, it's a real bummer these seem to be practically non-modifiable.

Still, an MI servo with a custom firmware for 270 rotation would be AMAZING.

Oh, btw, all of these respond to a 900-2100 uS pulse, I'd say the range is about 100.
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Old Nov 20, 2012, 09:50 PM
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wow gimbal mechanics is pretty cool. Hung my gimbal under a set of tall jakub legs for a static test with multiwii. Did some tweaking and things are looking good Finished dialing it in by bumping up the cc ubec a couple of tenths of volt and it seems pretty good. Now all I have to do is add the stuff that makes it fly
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Old Nov 20, 2012, 10:43 PM
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Originally Posted by pug398 View Post
wow gimbal mechanics is pretty cool. Hung my gimbal under a set of tall jakub legs for a static test with multiwii. Did some tweaking and things are looking good Finished dialing it in by bumping up the cc ubec a couple of tenths of volt and it seems pretty good. Now all I have to do is add the stuff that makes it fly
That sure looks really good. I like that abbreviated look! Now we are waiting for some test flights and video.

I finally get a break tomorrow and I am going to finish up a couple of gimbals I started.

I am also making a gimbal for my tripod and 55' pole. I went back to my original 16mm carbon tube setup since weight is really not a big concern. I am not flying it. I changed the roll axis into a pan axis with continuous servo and 7 to 1 gear ratio. I am using a Servo City servo gear box. Will get some pictures and post them up as soon as I take some.
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