Asked — Edited

Powerfull Robot .Safety Features

At present I am working on a Motorised Wheelchair Base unit using the original Motors,these are pretty powerful and can inflict a lot of damage if great care is not taken. Using my EZ-B to control its movement ,although it operates quit well, but for example if I loose connection for any reason the Robot can now be a monster out of control. To provide a safety feature to remove power from the motors one could use a micro switch on front & rear and once it meets an object it will stop. Good idea ,small problem it may be travelling at speed and you could sustain a serious injury if you happen to be that object.

My solution under construction at present, is use a Car Parking Radar which is stand alone and is not dependent on Ez-b or pc connection . To put it simply if an object is say within 10 ins of Robot ,power is cut off to motors. Then it can be reset through EZ-B if necessary

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Now that's a cool idea! I was worried about the same thing. I have had several instances when the robot decided to take off on his own while using EZ-B control. Don't know how because I did not click on the forward movement arrow. It just came on all by itself. eek

Could be an glitch caused by electrical noise I suppose. Yes we must all be aware how dangerous these things can be and strive to do our best to make them safe whatever it takes. I was thinking about putting bumper switches on him but was dreading it because of how it might look. I am also planning a remote controlled PANIC switch to cut power to the motors. You have spawned a more modern option. I will pursue it when I save up enough money. First I am ordering those IR Beacons we spoke of in the other thread.

So much to little time....

BTW please feel free to call me Rex


The digital ports will go OFF (negative) when the connection is dropped. I would connect a relay to a digital port via a switching transistor that controls the power to the motor controller.

When the connection drops, the motors will lose power.

Also, if you're using an 4 wire HBridge (not a serial/i2c motor controller), than you won't need to worry about it because the ports will turn off when the connection drops and the robot will stop.


Thanks DJ. Didn't know that about the Digital Ports. Then I can use an R/C controlled relay like the "Battle Switch" which can be controlled by a digital port directly.

I am already using one Battle Switch for the circuit I built that lets you electrically select between one of two dip switch settings. It works great. It is hooked to the Aux channel on my R/C receiver.

See thread

Dip Switch Configurator


Thanks Dj & Rex for your contributions I should have mentioned that I am controlling the original motor controller joystick with two servo motors, also I am using a servo motor from EZ-B to put pressure on a toutch pad to switch on and off controller.

Dj , you have recommended in a previous post to use a Sabertooth Motor controller of course you are right, but I like to use the original components.

So my issue is really when I loose power and say for example the robot is moving forward the servo will not return so it will keep going forward, and I cannot switch off controller also.

My solution to the problem Radar sensor now works independently of the EZ-B monitoring the distance to front & rear. That is connected to a relay that switches two pins on the XLR Charging connector,normally open, when closed power is shut to the motors .

Thought of using a relay between controller and motors but afraid it may damage the controller in the long term.

will upload diagram when complete to assist anyone thinking of incorporating similiar Pat


Bravia, I have the same dilemma. I am building a B9, also with wheelchair motors. I too, want to use the original controller from the wheelchair. I have the manual for the wheelchair, and it warns of possible radio interference causing a runaway. I like the radar idea. I might consider that myself, but I am going to install a final failsafe. The fictional robot had a power pack that would shut him down when pulled out. I am going to wire all of the motor power through that like a bus fuse. I am leery about depending on anything electronic, remote control, etc. I am sure that you could incorporate a panic switch that would be discreet, or disguised as something else, and then just stay within arms length when maneuvering in tight quarters, or around people.

A footnote.

I am also considering a second power pack, that when plugged in, will allow power to everything except his drive motors. I could use that, for instance, if he were outside giving out candy on Halloween, surrounded by children, or any other circumstance where I want to eliminate any possibility of him deciding to take a little stroll.


@Danger Well done thats a fantastic B9 Robot you are working on Yes I have personally had similiar instances where I attempted to hit a panic button , but all logic goes at that point.

having researched all my options Relays on motors ets I have decided that I would not place any cut off device between controller & Motors ( Relays especiallly may cause damage to the controller circuitry )

To this end I have discovered my controller charger is connected by an XLR 3 pin plug Once this is plugged into controller it shut off power to motors and disables controller safely. Remember the charger is not even connected to the mains input at this point.

On investigation I found two pins on the XLR plug are shorted out . Thats where I intend placing my Relay controlled by my limit Switch,Panic button and Ultrasonic Radar.

My proposal is to use possibly a card with say 5 relays the outputs connected in series to switch the XLR pins

1 :Panic Button 2: Ultrasonic radar 3: Front Limit Switch 4: Rear Limit Switch 5: Monitor connection from Ezb

Terms & Conditions 1 : This circuit would operate independently of the EZ-B ,although it would monitor its connection state. 2: It could be reset by the EZ-B but not overidden

Ps .if one has a similiar controller and is not familiar with charging circuits ets (the shorted pin in XLR PLUG is a safety device ) if you plug in the charger with the short removed ,you may not have a controller or battery to recharge. Pat


Yup ezb > switching Darlington transistor > relay like pictured here... User-inserted image

User-inserted image

It works very very well. Just remember the transistor opens to ground.


Yes possibly not sure current rating required must do a test hoping its milliamps

this is what I hope to use

User-inserted image


Did a test on switching off current on wheelchair controller only 1.3ma So Now I can loop a number of relays to shut down the motors in an emergency. big plus not switching high current also these relays have opto couplers for isolation


I agree with the idea and love the setup. I didn't go that deep for my bot. I just used to cheap big red E-stop button on it.. But that only works when some one is there. But this was my first scratch build so it wasn't running on its own. The one I am starting on now with some of the parts of the old one will move later so I am going to add your ideas into (if you don't mind, thanks)..


you are more than welcome to use also once I have circuit complete I will upload a schematic Pat


Pat That would be great. Thank you for the hard work.


Thanks for the compliments on my robot. Have you got any pictures of your robot yet? I would enjoy seeing it. That is interesting about the charging circuit for your wheelchair. My wheelchair has an onboard charger. I will have to look into that. It may have a similar setup. I wouldn't want to be pulling the power pack on a regular basis, but I do want to have a last resort method to stop him if he gets any crazy ideas. (Anyone who saw the first episode of "Lost in Space" will understand). Incidentally, I got the same relays for mine, except the "16" size. I haven't done anything with them yet. Be aware that when you power up the board they all flip. The controller de-energizes each relay on command. This isn't a huge issue. Because they are SPDT; you can wire them to either side, but they do draw power when they are in the "rest" position. You also have to plan around it for startup and shut down. Dave Shulpius bought some and pointed this out to me.