I have a hard time to get 2 HS-422 move at the same speed…
I have an idea but don’t know if it is possible to do. Easily
I have a small RC ESC witch i want to connect to the two motor. But that will give me only Forward and Reverse.
That when my idea came, can i hook 2 small relay to the BotBoard (bap28) and switch off one of the relay to turn.
(1 relay by wheel)
Anyone have try relay on BAP28 BotBoard ?
Tanks a lot !
If you are using an esc, you may want to bypass the servo control board inside the servo altogether. The ESC should be able to run the motors directly.
As for using relays, you will need to use a driving circuit to run the relay. Relays require a bit of power to switch which means your average micro can’t do it directly. You could use two BasicMicro Power Switchs which is probably over kill or two BasicMicro Bit Switchs. Both types are controlled via asyncronous serial commands and plug straight into the servo connector headers on the BotBoard.
Tanks a lot for the infos.
But at 19$ each (Need 2) i think the best is to buy a dual HBridge ? (many for 20$).
Or maybe there is a way to make the 2 HS-422 turn at the same speed… !
It’s for that project:
http://farm6.static.flickr.com/5258/5540669586_f2d8cf325d.jpg
Each servo is going to be different in that if you simply send 2000 to each, they will rotate at slightly different speeds. Just like 1500 isn’t exactly centered, you will need to offset the values you are sending to each servo. You shouldn’t need relays, motor controllers, or whatever to control the servos at the same speed.
Ok
But will it have good repetability ?
Yup. Once you find the offset, let’s say for example +37, you can always send 1537 to stop that servo.
Tanks a lot,
I will try that tonight. Will test how much offset i need to go strait… 
First off we need to properly define the problem. You are intending to “accurately” control a couple DC motors with no feedback. If we first agree it’s impossible, we can go into how to fail in the best way. lol The thought of sending both motors the same voltage from a single motor controller will not help as both motors/gear trains will have their own unique friction and looses. By using the two motors with their own built in motor controllers you will at least be able to give them their own speed command. Then it’s a matter of trial and error. Keep in mind the battery voltage will impact the rpm of the motors. The temperature will also effect it. Try to let the servos warm up a bit before trying to match the two motors speeds. Good luck!
Yes… i am in early stage…
I will include sensors to know the environement…!
Just want to start somewhere…
I understand that there is many things that can impact the speed they turn.
the typical R/C servos have a very small motor, but perhaps you could control them with the RoboClaw?
I’m currently modifying R/C servos to drive the motors directly, and power with an L293 dual H-bridge.
A BasicATOM Nano Driver Board (BM) or a Arduino motor control shield (board) will get you that. Or wire it up yourself!
I’ve even seen a little “secret” board that one of the vendors have that puts an L293D inside the R/C servo case!
http://www.solarbotics.com/assets/images/k_smd/ksmd_ps.jpg
These bridges driven by the uP take the pulse-width command and the pulse-stretching analog (?) circuitry out of the control loop.
If you then add wheel encoders (some bolt right up to the R/C servos), then control with a PID or PD control loop in the uP, you’ve got it!
RoboClaw does PID for you!
Alan KM6VV
