New Robot Application

Community General Discussions
1

Hello, all.  I am designing a speciality robot based on using electric wheelchair components.  One major difference is I want to have the robot wired to a simple joystick with a pretty long cable to the robot.  This cannot use RC because the robot will be in water, thus the need for a long cable to the joystick. 

My questions are as follows:  1)  Can I use a 100 ft. cable from the joystick to the robot? I have been told by a knowledgeable wheelchair mechanic that this is doable.  2) I only need the motors to go forward and reverse, nothing else, so will the regular joystick work?  3) Can I use some type of electrical converter or whatever to supply the needed DC to the motors through a cable or do I have to use batteries only at the bot?  4) Will the ECU (?) from the wheelchair still work with this configuration?  5) Are there any other components needed to make the basic unit work?  I can handle the water issues, just need to know that the idea for the wheelchair components will work.  Thanks for  your patience with the newbie questions.  Any and all help needed and appreciated.

2

Essentially an ROV

It sounds like you’re essentially creating an ROV. Although it might not have onboard intelligence, you’ll still likely be using most of the techniques employed. Blue Robotics makes a lot of accessories which you can use: https://www.robotshop.com/en/bluerobotics.html

Notice how they use a waterproof tether which is connected to a motor controller which controls the direction of the motor. This is a more involved approached, but there are reasons why it’s not direct connection. Almost all smaller ROVs have onboard power because of the losses in such a long cable. If you choose a good cable with low resistance which can provide 5V at the right current, you can use a DPDT relay to control direction. Ex: https://www.robotshop.com/en/12-vdc-dpdt-relay.html

It sounds like you’ll have some experiementation to do either way. Looking forward to other’s insights.

1)  Can I use a 100 ft. cable from the joystick to the robot?

Depends on the cable and if it’s carrying a signal or power.

2) I only need the motors to go forward and reverse, nothing else, so will the regular joystick work? 

Mos joysticks are analog - it sounds like you need a digital joystick, or a DPDT switch.

3) Can I use some type of electrical converter or whatever to supply the needed DC to the motors through a cable or do I have to use batteries only at the bot? 

Over a shorter length, sending power via wires would be OK, but you’ll likely encounter issues if with 100 feet of cable.

4) Will the ECU (?) from the wheelchair still work with this configuration? 

Where will you have it? If it’s on the ROV, then it should, provided it doesn’t get wet, and it receives the correct signal (which will be full speed since there’s no more analog)

5) Are there any other components needed to make the basic unit work? 

It sounds like your ideal would be to simply run a longer wire between the joysrick and the controller unit. Test some lengths and see if it works. Ethernet cable usually has low resistance.

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Reply

Cbenson,

Thanks for the input. Your input is most helpful. If I use agm batteries on board, underwater, in a waterproof case, should I reasonably expect 6-8 hours of life on a 150 lb. robot moving slowly on the bottom?  It sound like an ethernet cable to the bot controller (properly waterproofed) and a digital joystick would work.  Does it matter if the controller is at the bot or up near the joystick if I am only wanting forward and reverse on each motor (plus speed control)? Thanks again.

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The battery life depends on the capacity and total current draw. Water provides a lot more resistance than air (static and moving). 6-8 hours for most robots even on land is really high. You’d need an idea of the current draw of your system in motion in order to determine what capacity you need for a given period of time. For example if your system draws 15 Amps, and you wanted to operate for 8 hours, the battery’s capacity will (at minimum) need to be 15 x 8 = 120 Amp hours. Regarding where the controller is placed, it’s best to have it closer to the motors themselves, and ensure the signals being sent can reach the board (low current), rather than having wires carrying high current over a long length.