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.



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).



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


Here's are most of the parts Tony is pointing to that are cheaper and available from The Robot Shop here in the USA and other countries:

Large 6mm Set Screw Hub

Small 6mm Set Screw Hub

Aluminum Large "C" Servo Bracket

Aluminum Long "C" Servo Bracket

0.770" Clamping Hubs

0.625" Aluminum Clamping Hubs