I've been reading about various components that are attached to the ISS and occasionally see references to "remotely controlled bolts". That makes sense, but I've barely been able to find more than a reference to them with a basic Google search.

What do these bolts look like? Is it basically a standard bolt with a servo wrapped around it?


Maybe this cross section is more what you are looking for?

enter image description here

From here.

  • 1
    $\begingroup$ thanks- that shows it well. I'm looking forward to reading through that mechanisms doc. $\endgroup$ – tedder42 Apr 27 '16 at 20:39

Their name seems to be "Motorized Bolt Assembly", this is what they look like:


The servo is in the rectangular box marked BMA, the bolt extends through the fine guide cone.

More about the BMA (PDF page 89-102):

The Moog Space Station Bolt Motor Actuator (BMA) is a rotary actuator comprised of a brushless DC motor, controller, and 120V DC-DC power supply coupled to a four-pass planetary gear system and containing a manual override (MO) system. This paper discusses the new technologies developed and lessons learned during the BMA development. These include the use of a relatively new material, Pyrowear 675, a new Vapor Deposition coating, WC/C, and a hard-on-hard (HOH) worm drive system delivering 135.6 N,m (1200 in.lb) of torque (the primary focus of this paper).

The BMA is a rotary actuator comprised of a brushless DC motor, controller, and 120V DC-DC power supply coupled to a four-pass planetary gear system. The motor runs at approximately 3400 rpm, which results in 4.1 rpm at the BMA output (a 25.4-mm 16/32 female spline) at the end of the 833:1 gear train. Dual input electrical connectors allow powered operation from either of two independent Bolt Bus Controllers (BBC's). The electrical connectors supply power (120VDC), direction logic signal, redundant heater current, redundant RTD based temperature feedback, and limit switch pigtail pass-through lines. The limit switches are part of a customer-controlled mating assembly. The RTD's are customer-supplied (Boeing Part Number 1F08041-1) and the heaters are Kapton® 1 encased, inconel element, thermal foil heaters supplying approximately 28 watts per circuit. These devices were needed to maintain the electronics at or above -42.8°C (-45°F) while on orbit.

The brushless DC controller and DC-DC power supply were totally contained inside the unit on two independent multi-layered circuit boards. The dual power line inputs were Y'd internal to the unit and opto isolated at the board level. All electronics were designated "S" class or equivalent and rated for -53.9°C (-65°F) operation or colder. All precautions were taken to minimize ESD susceptibility, including the incorporation of soft EMI gaskets at the side cover interfaces. The brushless motor was designed and built by Moog Inc. and had a 51mm (2.0 in) OD by ~15mm (.6 in) stack length. The motor is capable of providing more than 3 times the required torque, but is current clipped by the controller electronics at about 1.5 times the required torque. Manual Override capability is supplied in the event of a power failure via a dual input, 10-mm (3/8 in), recess square drives. The dual input allows equal operation from two opposite sides of the BMA, meeting the requirement of a single unit to fit into one of four possible positions at the final level assembly in different orientations. The basic MO input of 50 rpm and up to 30.5 N-m (270 in°lb) of torque supply the same functionality at the BMA output as the powered main drive system. The effective gear ratio of the MO mechanism is 12.17:1. The MO utilized a unique worm drive arrangement to be able to function even with the motor through the third stage gear set jammed, and to meet the overall package size constraints. While the maindrive is running, the MO drive is held stationary via a "no-back-drive" device. Similarly, while the MO runs, the main drive must remain stationary from the third stage planetary output (fourth stage sun gear) to the first stage input (motor shaft). There was insufficient cogging torque in the base motor design to guarantee no rotation would be allowed during MO operation. This deficiency was overcome by adding a passive magnetic "cogging" unit onto the top of the motor. The cogging unit supplies -170 mN°m (24 in°oz) of torque statically, while only requiring 40 mA of driving force (or loss) during motor operation.

The PDF also contains photos, but unfortunately the PDF is a low-quality scan and the photos are nothing more than black smudges.

  • $\begingroup$ thanks! I see the "guide cup/cone" but is the bolt itself not shown? $\endgroup$ – tedder42 Apr 27 '16 at 16:44
  • $\begingroup$ Pretty sure that's just the fine guides, not the actual bolts. $\endgroup$ – Nathan Tuggy Apr 27 '16 at 20:27
  • $\begingroup$ @tedder42: thebolt is in the middle of the fine guide cone; see page 25 of the document Hobbes linked for a crossection with the cone and cup mated and the bolt engaged. $\endgroup$ – SF. Apr 27 '16 at 20:30
  • $\begingroup$ that's a great document- I assume the bolt was just hidden in the cone/not exposed in that picture. I'm going to accept the other answer but it's really a combination of these answers that provides the overall picture. $\endgroup$ – tedder42 Apr 27 '16 at 20:37
  • $\begingroup$ wow- just saw the update. great information. $\endgroup$ – tedder42 Apr 28 '16 at 17:26

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