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Sienna
Joined: 20 Jan 2008
Posts: 4
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 Posted: Wed Mar 26, 2008 11:03 am Post subject: Hobbico CS-170 |
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[go check Tower for the specs, as I can't link]
Has anyone used an open servo in the really high torque servo cases? The CS170 appears to be a HSR5990TG (based on the heatsink in the case). The 5990 is rated to stall at 4.2A @ 6V.
Can the Openservo withstand those currents? Does anyone know if it fits in that case?
I bought some 5990s with the hope of using the HMI protocol for feedback, but it appears as more information comes out HMI actually disrupts servo operation. So now I am looking at alternate control methods.
Thanks! |
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kbb
Joined: 01 Jun 2007
Posts: 180
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| Posted: Wed Mar 26, 2008 11:59 pm Post subject: Re: Hobbico CS-170 |
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| Sienna wrote: | [go check Tower for the specs, as I can't link]
Has anyone used an open servo in the really high torque servo cases? The CS170 appears to be a HSR5990TG (based on the heatsink in the case). The 5990 is rated to stall at 4.2A @ 6V.
Can the Openservo withstand those currents? Does anyone know if it fits in that case?
I bought some 5990s with the hope of using the HMI protocol for feedback, but it appears as more information comes out HMI actually disrupts servo operation. So now I am looking at alternate control methods.
Thanks! |
Click here for someone else’s comment about the CS170 that may be useful.
The OpenServo V3 boards that Jay sent me have FDS9934C FETs, so I think you could theoretically get up to 5A through them (max continuous current for “Q2”). However, the implementation of the OpenServo board means that there would be a big problem with heat dissipation. I have added heat sinks to mine (click here to see commentary/pics and other links about that). I have managed to push around 3A thu one without it blowing, but it wasn’t left running that way for long.
Using the V3 boards with higher currents would necessitate changing two of the resistors as the on-board current measurement in the standard design is scaled for a maximum of 2A plus R2 may need to be changed for higher currents to remove the risk of it burning out (click here to read about this). A similar issue about the onboard battery voltage measurement is also discussed near there.
I haven't yet finished cabling up my robot, once that is done I will be in a better position to report what happens during “real use”.
I don't know whether the OpenServo boards will fit inside either a CS170 or a HSR599XTG. If you happen to come across some pictures showing the “electronics bay”, that might help us guess. A small amount of cutting and trimming was involved in mounting them inside the MG995- which seems to be about the same as most standard servos in terms of available space inside. But bare in mind that heat sinking would need to be accommodated because of the higher currents.
It would be well worth fully testing the combination before committing!
Kevin. |
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Sienna
Joined: 20 Jan 2008
Posts: 4
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| Posted: Thu Mar 27, 2008 2:50 am Post subject: |
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I like your heatsinks! (and the bipod!) I wanna know how it does when you get it all wired up!
On the CS170, that is a good link, that we are not sure if it uses a cheaper cored motor or not. I am almost tempted to buy one just to investigate.
I actually took apart one of my HSR5990TGs today, and got a couple of macro photos of the circuit board, both sides. The key difference in the 5990 design, and a normal servo, is that the 5990 places the circuit board right under the plastic end piece. So, if I were to use your heat sink design, that would stick out farther. When my webserver is up again, I will post the photos.
Now, as to the voltage / current measuring... Did those changes get made in V3? Or do they need to be done still by hand? I didn't get a firm sense either way from reading the thread.
Thanks again,
Caitlyn |
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kbb
Joined: 01 Jun 2007
Posts: 180
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| Posted: Thu Mar 27, 2008 8:51 am Post subject: |
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| Sienna wrote: | | Now, as to the voltage / current measuring... Did those changes get made in V3? Or do they need to be done still by hand? I didn't get a firm sense either way from reading the thread. |
On the early pre-built boards I got from Jay he seems to have changed R2 and R3 to .022 and 7.50K as described in one of those links (as far as I can tell: the 0.022 is too small a value to be testable with my multimeter and is not labeled). That makes for a maximum practical current of 2.75A-assuming sufficient heat dissipation.
The voltage and back-EMF resistors were as specified in the schematic, so I changed those by hand.
If you are going to get one for testing, etc., you could email Jay or Barry and ask what they are shipping them with at the moment or whether you can get a “special order”.
See here for info: Buy OpenServo
Kevin. |
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bren
Joined: 01 Jul 2007
Posts: 79
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| Posted: Thu Mar 27, 2008 11:16 pm Post subject: |
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I will add my two cents.
I have KONDO 766 which people say that stall at 3A but I have been using them for 1.5 years and converted them to openservo. Over this time I have never seen them go over 1A even when stalled with me trying to make them move. So I would say that the openservo would be alright for your purpose. I would buy one board and convert one servo. It's quit fun and gave me some good knowledge about the sevo and how they work.
Bren |
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