Hello there,
I have little RC Ride On car which I`m trying to modify for my little son.I installed LED lights and added 3 extra batteries so the car goes about 5h now without need to charge. The car works perfectly on remote controller but i would like to get it to work over the phone. I already have schematic, mobile app, and code for arduino that i successfully tested with two small RC car that i was able to modify. Right now its time to get that logic in that big ride on car. I am trying to find the motor shield that will allow me to control 3 DC motors ( 2 for movement and one for direction) I tried to find what is the power of these motors but i couldn't find anything on them. So i measured the Amperage with car in motion while my son is driving. The amperage per motor is about 5A. So i am looking something that will handle that. Preferably H bridge which can run 3 DC each up to 10A.
Does anyone know where i can find that?
I have been goggling for few days now and i couldn't find anything good.
Any ideas?
Slavisha
The down and dirty way would be using a relay shield to drive the existing relays on the board. May cost you $8.00
You should find the stall current for the motors, motor controllers have to handle that
without exploding (usual failure mode), so its important.
The stall current just depends on the supply voltage and the resistance of the motor
which can be measured (although its usually a very small resistance and a 4-terminal
Kelvin measurement may be needed to get accuracy).
For smaller motors you can lock the rotor in place and measure the stall current
(note this gets dangerous or life-threatening with large motors, if unsure don't
attempt).
[ I should clarify its the MOSFETs in the motor controller that burst, not the whole thing! ]
Thank you all for quick response.
I havent try to measure the Amperage of the motor while rotor is blocked but i found small specs when i took motor out of housing. Please see attached pic.
What apears to be a model of this motor is SF550-C. It is 12v with 9000rpm. And i am not certain what other two number means.
Can this help?
I cant find this model number on google so i am wondering if its really model number of the motor.
Slav
Ok, so apparently two Relays 30A each has been used to drive this RC car. I have not worked with relays before so i have few questions.
-
Can relays be wired to control DC motor to spin in both direction? I think thats what they done it here originally is that correct?
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Since i cant find Arduino compatible 2 channel above 10A per channel, i am planing to buy 4 channel relay with 10A per channel and wire each motor independently, dedicating one relay to each motor. Would this be a problem?
-
The reason i am buying 4 channel relay is because i want those LEDs under the car to be controlled by it too since they require 12V which i couldn't get out of Arduino. Will this be smart idea?
Initially i will have 1st channel dedicated to right movement motor, 2nd channel to left movement motor, 3rd channel to direction motor and finally 4th channel to the LED lights. Channel 1 and 2 will be controlled always in same time so the car can be in motion by left and right motor in same time.
Will this idea work?
Heres the link for the relay
http://www.ebay.com/itm/5V-Four-4-Channel-Relay-Module-With-optocoupler-For-PIC-AVR-DSP-ARM-Arduino-8051-/310574401892
This is what I was refering to in my post. However I would simply hack in to the existing board and use the relay from the shield to drive the 30 amp relay. The existing relays are 30 amp for a reason. I have not found a cheap 30 amp spdt relay shield. so a relay driving a relay is the down and dirty way.
You can purchase a standard shield that stacks on to an arduino.
Yes you can use two spdt relays to run DC motors forward, reverse, and have a breaking function as well. i have included a link below.
Great,
thank you for your response Weldsmith. I think your suggestion to tap in to existing circuit might be easier so i can avoid all wiring and stuff again. When you said i can get standard shield to stack on top of the arduino, to which shield you were referring to?
I have Motor Shield from adafruit, version two, but i think you were having something else in mind.
Thank you again.
Slav
You are right I was not thinking of a motor shield at all. you are on the right track with the relay shield you have shared with us on your post, as far as I can tell this one will not mount on the arduino. look on ebay and you will find relay shields that will stack on to an arduino. This saves a little bit of wiring. just look in the description and make sure the pins are compatible to the arduino you are using.
Awesome. I will give it a try. Thank you so much.
Slav
4 10A relays in parallel will not switch 40A, they will switch 10A. Mechanical relays
will operate at slightly different times so the first to make contact will be the one that
welds shut(*), the last to open will get all the arcing from the inductive load of the motor.
All you do is waste 3 relays
(*) 4 times the current is 16 times the heating power.
Tried searching for 11V Brushed ESC's in the 100 to 400A range? RC ESCs are
probably the cheapest option for a controller, but make sure its for brushed motors,
and reversible.
Hi Mark,
I was not trying to switch 40A. What i was trying to do is to use 1 relay to initiate let say left motor to drive in on direction, and second relay will drive the motor in opposite direction. Both of these relay will never be on in same time. Car will go ether forward or backward depending of the state of these two relays. Now, i purchased this relay below that is compatible with Arduino. What i am going to do is use 4 relays on left to drive 2 motion DC's and 2 relays on right to drive direction DC. And i will use one of the two renaming relays to control LED light.
So the plan is this:
Relay 1 - Left Motion Motor forward
Relay 2 - Left Motion Motor backwards
Relay 3 - Right Motion Motor forward
Relay 4 - Right Motion Motor backwards
Relay 5 - Direction Motor to turn left
Relay 6 - Direction Motor to turn right
Relay 7 - To control the LED lights
Relay 8 - spare to connect anything else.
If i try to move the car straight forward, Relay 1 and Relay 3 will be turned on and both motor will use less then 5A per relay to drive the car.
If try to move the car forward and to left Arduino will engage Relay 1+ Relay 3+ Relay 5. Each relay will handle less than 5A in this case but they will do this in same time.
Do you see any problem with this?
Thanks for all your advises.
Slav
Slav, You missed what MarkT was trying to tell you. These relays are not rated for the amperage that you need.I suggested that you simply use one of the relays to drive the existing (30 amp)relay. So for each relay that is in use on the car you will need another to drive it, or you can find a motor controller that will handle the motors (kinda spendy).
How is the car physically steered. this part of your project description has been left out until now. In your last post it shows you intend to use a motor to turn the front wheels. do you have a picture of that system? Is it another relay board?
I apologize for confusion guys.
The direction of the car is also managed by RC controller right now. So my confusion was how did they managed to control 2 DC motion motors and 1 direction motor with two relays? But now when you mentioned it might be that another relay is somewhere else in the car. I will try to take the car apart and see if there is one.
Slav
There are setups that use a DPDT relay to control direction, and a MOSFET to handle the PWM speed control. In these setups the MOSFET is off anytime the relay poles are being changed to prevent arcing.
Ok, i opened up the car and i could not find 2rd relay anywhere. But please take a look the image of the Remote control receiver that is connected to the board with two Relays i showed in one of earlier posts. Now, in order to go the route you suggested by using existing electronics, do you think i could just unsolder this receiver from V,B,-F,+R and L pin and to these pin connect Arduino with prepared Bluetooth and designated pins?
This way i am really just attaching arduino to existing mechanism and replacing small RC board with arduino.
I think yes. You need an arduino, Blue tooth shield and relay shield. The arduino will not run the existing relay with out going through another relay first. The output of the arduino does not have the right voltage or enough amperage to drive the relay.
Slavisha:
Here is what the car currently using for RC control.
When you say this - you mean the ride-on vehicle?
If so - then there should be a way to remove the R/C portion of that circuit (which is likely the vertical component "daughterboard" on that relay controller you show), and control the relays with the Arduino, using a standard transistor/mosfet drive on the coils. If you've already modified some small R/C cars to do this, it shouldn't be a big stretch for you to reverse engineer that relay board.
Alternatively, you could get a couple of 30/40 amp SPDT automotive relays - wire those in an h-bridge fashion to control the motor; speed control would be a different matter (cheapo way is an n-channel mosfet on the low side between the relay h-bridge and ground, with the fet rated for the current).
Lastly - look up the "modified powerwheels" forum - plenty of threads there dealing with -exactly- what you are trying to do.
One relay to switch both drive motors, one for the steering? A DPDT relay or switch is
equivalent to an H-bridge.