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Asked — Edited

Bosch Motors With Integral Potentiometer

As I have now sent quite a few Bosh motors to friends here on the forum (Steve, yours are on their way) and also after reading Dave's well written review, I thought it would be good to give more information on these motors to the group.

Without modification the motors have 100 degree of movement, once you cut off the actuator arm (to get the 6mm spindle) the motor will rotate 360 degrees there are no internal stops. The internal pot is only active for the 100 degrees.

I needed 180 degrees turn on the EZ:1 and EZ:2 head pan smart servo (shown below) and I achieved this by modifying the smart servo firmware so that when the smart servo controller gets 2 to 99 it accurately moves through the whole 100 degrees and if I send 1 or 100 then the controller sends the motor 40 degrees past the 100 degrees in both directions. Centering the servo (back to 50) always accurately re-syncs the motor position as it is half way into the pots travel.

User-inserted image

To get the original actuator arm off, very carefully with a hacksaw blade cut down one side of the actuator to reveal one side of the spindle, once this is clear then with a gentle prying from below the actuator the arm usually just pulls off.

Here are the 6mm hubs that fit the motor spindle.


Here is the plastic box that holds the smart servo PCB.


Here is more info on the motor drives


Hope this is of use.


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Tony, are you still selling these to people on the forum? If so how much? I may be interested in a couple...



I heard there was a retailer in the U.S. but I can't seem to find it. Anyone know if you could buy them here?


@Herr Ball

Search for Heater A/C Air Flap Control Motor - 4B1 820 511 K 98-05 Audi A6 S6 RS6 Allroad

also see


The part number is 4B1 820 511 K. This is the same part number as the one Tony uses. I have seen other motors available with letters on the end of the part number other than K but I don't know if they would operate with the same torque. So be careful when searching. I have seen prices for used motors from $14.29 to $24.95. I found one site that sells new ones and they cost around $172! sick


Thank you for sharing that information Tony and rgordon!


Interesting.... So this is actually designed as a car part. That explains the unwillingness of Bosch to distribute to the hobbyist market in the US. In addition to eBay, we might be able to find used ones at car junk yards, or new ones from Audi dealers or auto-parts stores (assuming that the US version of the 98-05 Audi A6 uses the same part or one that is functionally equivalent).


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New from Audi is likely to cost a small fortune, as pointed out by Rex.


"New from Audi is likely to cost a small fortune, as pointed out by Rex."

True that, but at least a possible source if you just have to have one and don't trust used...



Thanks Tony for posting this info. After working with these motors I felt they needed a thread of their own here

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Thanks Dave, for the additional information.

For those on the group that may have not seen these Bosch motors in action, here is a video of the EZ:1 5DOF arm in action.

Each smart servo has a blue LED status/debug indicator and they do relay a lot of information on what is happening with the servo itself.

I would like some feedback from the group on these LEDs, do you think they currently look too much (like a Christmas tree) or do you think they look ok? I am wondering about reducing the flashing or using duller colours that do not stand out so much. Thanks in advance to anyone who gives their opinion!



Keep the lights just as they are. People love lights. It make the bot look functional, processing information and ties it into what people expect from robots. All the classic robots from the past has blinking lights. ;)

Duller lights are a matter of taste. I love lights but don't like them to blind. Sometimes less is more. Anyway, can you add a user controlled dimmer? That totally puts the decision in the hands of the end user.

You should give your bot a British accent. You guys over there sound so cool when you talk. The ladies sound sexy. I have my GPS in the car set to a female British voice. It sounds just like Claudia Black in Farscape.

Sorry for going off subject but Claudia flips my switch. :D


But isn't she Australian? She sounds Australian to me.


Agree with dschulpius ... my thoughts exactly.


Aussies are cool also. That's another accident I love. The Scots got it going also but it's hard for me to understand that one.


Australian ! Close enough

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Dave, your comments are interesting about the English accent, I went out of my way to give the EZ:1 and EZ:2 robots American accents as I thought that would be the most preferred! I had no idea people would want English accents on their robots in the US, but now coming to think of it on a few of my US business trips people have said to us "I just love your Australian accent" so people in the US must think I sound Australian too! I have trouble with understanding the Scottish accent as well.

Glad you like the LED's. its was one of our design team that said "it looks like a Christmas tree" and that got me thinking that maybe the flashing was too much. I might just reduce the scan flashing so it only flashes debug info.



Tony, I like the LED lights, especially if they are relaying useful information. That makes them more valuable then just having displays for show, they are functional and purpose generated. I guess a dimmer or toggle switch option would be nice, if not too pricey. I would just leave mine on. Can I order my female robot with a slight British accent? That still amazes me how an arm that long can lift that beverage so well and quietly. Thank You, Steve S


I agree with Dave and Steve! Keep the lights but maybe offer an option to turn them off.....My robot FRED has the voice Lawrence from Cepstral and a few others..But yeah british accents sound to me James Bondish? British butler?... and just foreign enough!


The British accent was the whole reason I chose Lawrence from Cepstral.com. I also mixed it with the "old robot"sound effect. I think British accents are the coolest.