Running dual ESCs on a single battery?
02-10-2015, 05:28 AM
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Running dual ESCs on a single battery?
Hi guys,
First off, let me apologize if this isn't the right section. My question is about Emaxx components, so I felt like this is the right place to ask. If not, feel free to move this thread to somewhere more appropriate.
Anyway, I am designing a vehicle for a mechanical engineering design competition that my college is hosting. For a variety of reasons, I decided that a vehicle with tracks would be the best option. Think of a tank with a flat chassis in the center. In order to make this work, I am going to try to run one motor powering each track.
This is where my question comes into play: I am given a very tight budget. I can find 2 Emaxx ESCs and Titan 550 motors that fit into my budget easily, and I am certain they will provide more than enough power to throw the 5lb vehicle around. The tricky part is that we are penalized for power consumption of our vehicles, so I need to keep the battery power as low as possible. I feel pretty sure that I can hook up each ESC to the receiver (using a decent grade Fubuta RX/TX) and run them individually, but this is going to require at least 1 7.2v battery running each motor. Would it be possible for me to solder up a harness that allowed both ESCs and motors to run off of 1 7.2v battery, or is this just going to kick the ESCs off because of some built in low voltage failsafe? Longevity is not really an issue: the competition only allows 3 minutes of run time max, and I suspect it will take a well-built vehicle about half that time to run the course.
Thank you all for the help!
First off, let me apologize if this isn't the right section. My question is about Emaxx components, so I felt like this is the right place to ask. If not, feel free to move this thread to somewhere more appropriate.
Anyway, I am designing a vehicle for a mechanical engineering design competition that my college is hosting. For a variety of reasons, I decided that a vehicle with tracks would be the best option. Think of a tank with a flat chassis in the center. In order to make this work, I am going to try to run one motor powering each track.
This is where my question comes into play: I am given a very tight budget. I can find 2 Emaxx ESCs and Titan 550 motors that fit into my budget easily, and I am certain they will provide more than enough power to throw the 5lb vehicle around. The tricky part is that we are penalized for power consumption of our vehicles, so I need to keep the battery power as low as possible. I feel pretty sure that I can hook up each ESC to the receiver (using a decent grade Fubuta RX/TX) and run them individually, but this is going to require at least 1 7.2v battery running each motor. Would it be possible for me to solder up a harness that allowed both ESCs and motors to run off of 1 7.2v battery, or is this just going to kick the ESCs off because of some built in low voltage failsafe? Longevity is not really an issue: the competition only allows 3 minutes of run time max, and I suspect it will take a well-built vehicle about half that time to run the course.
Thank you all for the help!
02-10-2015, 06:31 PM
#2
The EMaxx EVX esc is designed for two 7.2v batteries and the esc makes a serial connection inside the esc. So a single battery isn't going to work with this esc. The EMaxx Titan 550 motors are 21t and can be run on up to 16.8v while the other Titan 550 (Rustler, Slash, etc) is a 12t and is for up to 8.4v. The 21t Titan can be run on 7.2v if desired. Either way you need to ditch the idea of running the EVX esc off a single 7.2v battery, staying with Traxxas, the XL5 would be more appropriate.
As for running two esc's off of one 7.2v battery, yes it can be done. You obviously know about voltage drop and are concerned there will be too much voltage drop with two esc's. The low voltage cutoff you refer to is something most modern esc's are equipped with to protect Lipo batreries from going to low. Generally the esc cuts power to 50% when the voltage threshold is reached and only cuts power completely if you continue running and the voltage drops further. This feature can be disabled on all the esc's I know off (sometimes called NiMh mode) so it won't shut down the esc's.
Edit: I recommend doing some math and figuring out what battery combination will result in the lowest penalty. If the penalty is less for dual 7.2v 2500mah batteries than the penalty for a single 7.2v 5000mah battery then I'd go with the dual battery option. a separate power source for each esc would be better plus it has the option for a serial connection for higher voltage.
As for running two esc's off of one 7.2v battery, yes it can be done. You obviously know about voltage drop and are concerned there will be too much voltage drop with two esc's. The low voltage cutoff you refer to is something most modern esc's are equipped with to protect Lipo batreries from going to low. Generally the esc cuts power to 50% when the voltage threshold is reached and only cuts power completely if you continue running and the voltage drops further. This feature can be disabled on all the esc's I know off (sometimes called NiMh mode) so it won't shut down the esc's.
Edit: I recommend doing some math and figuring out what battery combination will result in the lowest penalty. If the penalty is less for dual 7.2v 2500mah batteries than the penalty for a single 7.2v 5000mah battery then I'd go with the dual battery option. a separate power source for each esc would be better plus it has the option for a serial connection for higher voltage.
Last edited by Maj_Overdrive; 02-10-2015 at 06:39 PM.
02-10-2015, 06:56 PM
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The EMaxx EVX esc is designed for two 7.2v batteries and the esc makes a serial connection inside the esc. So a single battery isn't going to work with this esc. The EMaxx Titan 550 motors are 21t and can be run on up to 16.8v while the other Titan 550 (Rustler, Slash, etc) is a 12t and is for up to 8.4v. The 21t Titan can be run on 7.2v if desired. Either way you need to ditch the idea of running the EVX esc off a single 7.2v battery, staying with Traxxas, the XL5 would be more appropriate.
As for running two esc's off of one 7.2v battery, yes it can be done. You obviously know about voltage drop and are concerned there will be too much voltage drop with two esc's. The low voltage cutoff you refer to is something most modern esc's are equipped with to protect Lipo batreries from going to low. Generally the esc cuts power to 50% when the voltage threshold is reached and only cuts power completely if you continue running and the voltage drops further. This feature can be disabled on all the esc's I know off (sometimes called NiMh mode) so it won't shut down the esc's.
Edit: I recommend doing some math and figuring out what battery combination will result in the lowest penalty. If the penalty is less for dual 7.2v 2500mah batteries than the penalty for a single 7.2v 5000mah battery then I'd go with the dual battery option. a separate power source for each esc would be better plus it has the option for a serial connection for higher voltage.
As for running two esc's off of one 7.2v battery, yes it can be done. You obviously know about voltage drop and are concerned there will be too much voltage drop with two esc's. The low voltage cutoff you refer to is something most modern esc's are equipped with to protect Lipo batreries from going to low. Generally the esc cuts power to 50% when the voltage threshold is reached and only cuts power completely if you continue running and the voltage drops further. This feature can be disabled on all the esc's I know off (sometimes called NiMh mode) so it won't shut down the esc's.
Edit: I recommend doing some math and figuring out what battery combination will result in the lowest penalty. If the penalty is less for dual 7.2v 2500mah batteries than the penalty for a single 7.2v 5000mah battery then I'd go with the dual battery option. a separate power source for each esc would be better plus it has the option for a serial connection for higher voltage.
My mistake on the ESCs... I knew that the Emaxx had the ability to run dual batteries, but I was not aware that it was required. It looks like the Rustler XL5 ESC is roughly the same price, so I have no problems going with that option instead. You are correct, I was concerned the voltage drop from the dual ESCs setup with only 1 battery.Great info on the NiMh mode as well, that is a large burden off of my shoulders for certain. I will also look into changing this setting on the XL5 ESC.
As far as the penalty for power goes, here is the equation that our scores are calculated off of: Score = Payload/(time*(voltage*mAh)). Running 2 7.2v 2500mAh batteries would reduce my score the same amount as running 1 7.2v 5000mAh battery assuming I dropped the same payload in the same amount of time for both runs. The problem is this is still an enormous reduction my score... 1/36000 to be exact. I think I will try to find a cheap 1800mAh battery from Tower, and run that seeing as that would only be a reduction of 1/12960.
Thanks again!
