DARPA style RC car... sorta

Heya
I'm turning an RC car into an autonomous vehicle, and I have a leetle question. I'm planning to go cheap and use the BOE bot that I already have to be my controller.
My question is whether or not it would be safe/possible to hook up my RC car's speed controller to the BOE bot. It has PWM inputs, so it hook up fine, no hacking there. The worry that I have is that the RC radio doesn't have it's own battery, it just uses the one from the speed control. Would there be any risk hooking up the speed controller to the BOE bot? Programming comes second, it's the mechanical I gotta figure out first...

[sciguy125]

First off, you need to figure out what is powering what.

I presume that since the radio reciever is powered from the speed controller, it outputs voltage on the PWM cable. However, you should verify this first. Connect a cable to the speed controller and turn it on. See if there's voltage between power and ground (red and black, respectively) on the cable. If there is NOT voltage, you shouldn't have any problems with just plugging it in. If there IS voltage, I see two options.

1.) Somehow disconnect the red wire when you connect the two devices. It's generally not good to connect two seperate power supplies together, hence, you don't connect them. But, as long as they have a common ground (black wire), they should still play together nicely.

2.) Run the BOE bot controller off of the speed controller's supply. This is the better option. I'm not personally familiar with the controller, but you should be able to find a way to run it off of the power coming in on the PWM cable. Depencing on how it's designed however, you might need to splice some wires. Before you do this, however, make sure that it's giving you the proper voltage.

Alright, so I hooked up my multimeter to the PWM coming off the speed controller. There is voltage coming out, about 7.2 volts of it (this makes sense, because that's the voltage of the battery I'm using). Anybody know if this would work keeping the PWM intact when I hook it up to the BOE bot?

[edit] this is, it turns out, the same voltage that the BOE bot uses. So in theory, I should be able to run the BOE bot off of the car's battery... Any ideas on how I could go about doing this? [/edit]

[sciguy125]

Originally Posted by 114ManualLabor

Anybody know if this would work keeping the PWM intact when I hook it up to the BOE bot?

In my own experiments, the R/C reciever outputs a 3V signal seemingly regardless of the supply voltage. Your controller will probably be putting out a 5V signal. It should be fine.

Originally Posted by 114ManualLabor

[edit] this is, it turns out, the same voltage that the BOE bot uses. So in theory, I should be able to run the BOE bot off of the car's battery... Any ideas on how I could go about doing this? [/edit]

You can connect the battery to both devices by using a Y connector. I'm not sure if you can buy one, so you'll probably have to make one.

See if the BOE bot's PWM output is connected to the supply. Check if there's continuity between the supply lines on the PWM cable and the battery terminal. (check for continuity between the red wire and + battery terminal, then check for continuity between the black wire and - terminal) If there is continuity to BOTH, you can just connect the BOE bot to the speed controller without any problems.

If there is NOT continuity, you'll have to separate the BOE bot outputs from the supply. On the speed controller end, the supply lines on the PWM cable are connected to the supply. So, you'll have to make sure that you DO NOT connect the red wire on the BOE bot side. Well, it doesn't really matter which side is disconnected, just make sure that the power line doesn't connect the two devices. Having ground connected shouldn't be bad, and may actually be better.

Thanks a ton, I'm gonna be trying this out soon, after I ask the electrical guru on our team.

I'm now realizing that I should have included this in my last post, but it's kinda too late to edit... ah well

so anywhoo...
I now know how to hook it all up and all that fun stuff. The only thing that I'm unsure of is how to get actual variable speeds with the motor. So far I can only make it go full out, and then not at all. Anyone know how I can program it so I can get variable speeds? I'm using a BS2, using Pbasic v 2.5.

[sciguy125]

Can you post some code?

I assume that if you've gotten it to work, you know what the signal looks like. 1ms for full reverse, 2ms for full forward, 1.5ms for neutral. If you want speeds in between, just change the length of the signal to be between the extremes. i.e. half speed forward would be 1.75ms.