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        Discussion Help me figure something out, anyone used a servo driver to control an ESC?

#1 Scott_NJ Oct 11, 2012 02:10 PM

Help me figure something out, anyone used a servo driver to control an ESC?
 
Hey guys, bit of an odd question and thought someone here might be able to help. I'm modifying a power wheels ride on toy and looking to replace the on off switch for power with a car esc.

The motors are not brushless and I think a pretty stock mabuchi style 540???

My thought is to use a brused ESC connected to a servo driver and then replace the dial on the servo driver with a horn of some kind linked to the gas pedal in the car.

Anyone know if this will work, and can anyone suggest what ESC might work? I would be powering with 3 6V sealed power supply batteries in series, so 18V, and then its driving two motors with a Y connector. I expect the AMPS to be in the 30-40 range max.

-Scott

#2 wparsons Oct 11, 2012 02:20 PM

Any servo tester should work, as for ESC I'm not sure what would handle the voltage and load.

#3 Jeremy Kamutzki Oct 11, 2012 03:45 PM

there's this
http://www.ebay.com/itm/Motor-Speed-...item1e6c4c52bf

but you'd need a separate BEC because input voltage is only up to 17v. I just googled 50A brushed car esc and got lots of results.

#4 Scott_NJ Oct 11, 2012 06:45 PM

Jeremy thanks, yea something like that would work I think. I am thinking if I can make up a control horn on the pot, then I can mod it for a second pedal. Gas from neutral forward, and then a brake / reverse pedal to the other side of the horn to put brakes on and back up.

As for voltage, since I am feeding really with three 6V's, I can just tap off two of them for 12V input into the ESC.

Any reason a servo tester should drive the ESC?

And thanks guys!

#5 wparsons Oct 11, 2012 08:23 PM

What pot are you planning on hooking up a control horn to?

A servo tester sends the signal to the servo to make it move just like a receiver would. An ESC runs off that exact same signal, so a servo tester will do the same thing with an ESC.

I'm a little confused by how you plan to power it with three 6v packs, but only put two of them into the ESC? If you want to run 18v, all 18v need to go through the ESC. You can't send half the power through the ESC and just add in more between the ESC and motor.

#6 Scott_NJ Oct 12, 2012 08:46 AM

WParson, a servo controller uses a potentiometer to let you travel the servo that is hooked up to it. So it sits at neutral and then you can cycle it left or right.

My thought is in theory on an ESC you can sit at neutral and then cycle towards forward, and then towards brake / reverse. Instead of turning that pot by hand, I would try to hard mount it below the pedal. I probably need to rig up some sort of spring on it though like the old servo keepers to make sure that if my kid jumps on both pedals it doesnt just tear the thing out of its mount.

As for the voltage, I see what you are saying, I was thinking I could run all 18 into the power side of the ESC, but use 12V to power the servo tester instead of the output from the BEC circuit in the ESC. That might not work though...


Quote:

Originally Posted by wparsons (Post 22977256)
What pot are you planning on hooking up a control horn to?

A servo tester sends the signal to the servo to make it move just like a receiver would. An ESC runs off that exact same signal, so a servo tester will do the same thing with an ESC.

I'm a little confused by how you plan to power it with three 6v packs, but only put two of them into the ESC? If you want to run 18v, all 18v need to go through the ESC. You can't send half the power through the ESC and just add in more between the ESC and motor.


#7 wparsons Oct 12, 2012 03:27 PM

If the ESC can't handle the full 18v, it'll blow regardless of how you're powering the servo tester.

I was confused about the pot because it sounded like you were asking why to use a servo tester at all. I'm thinking something like a flexible pushrod from the pedal to the horn on the pot could work. That way if they jump on both pedals the cable will flex instead of braking anything off of mounts. You'll also need to "connect" it to the horn in such a way that turning the other way doesn't push the opposite pedal further out (kinda like the brakes/carb linkage on a nitro car)

How do you plan to handle reverse? Having a kid hit the brakes, then hit them again and go in reverse could give them quite the shock if they were just hoping to stay stopped.

#8 Scott_NJ Oct 24, 2012 07:33 AM

WParsons, thanks for the response, flexible cable like used on the planes could be a great idea to drive the servo tester, that way I can also mount it wherever I want.

On the reverse, that is a good question. The basic set-up of these cars uses a switch to change polarity on the motors so they stop, and then switch into reverse. It might be easier to keep that set-up and just use an ESC set up to apply brakes when you let off the gas.

Scott


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