I'm building a rotating lamp for a small DIY project to learn about motors and timing belts/pulleys. As I am learning, finding parts that are small enough, fit a stepper motor shaft and reasonable priced is difficult.

I am trying to find a way to turn a lazy Susan that has a slip ring through the center within a space of about 6-8 inches. The slip ring is so that I can get electricity on the top with it still being able to freely turn.

Timing belt Mechanism


  • What are the usual increments of timing belts? On Robotshop I found 8 in and 25in and that is it. To me this seems like a small range. Is this normal and have people found better supplies to offer a wide range of timing belts....in something like 1 in increments.

  • How much slop is in the timing belt? When attaching two timing pulleys do you usually have to add idlers or stretch out one of the wheels to get a good fit?

  • How close can timing pulleys be before there is not enough threads to move.

  • $\begingroup$ Welcome to Engineering! I edited your title to better represent what I understood to be most of your question. The edit also avoids the shopping question aspects, which are considered off-topic for this site. $\endgroup$
    – Wasabi
    Commented Feb 27, 2018 at 2:55
  • $\begingroup$ Similar here : engineering.stackexchange.com/q/6888/10902 $\endgroup$
    – Solar Mike
    Commented Feb 27, 2018 at 20:24

2 Answers 2


I tried both ways, idlers and slide, with and without additional spring.

A) Idler with spring tends to oscillate when load torque is not constant (it is rarely constant).

B) Sliding motor and spring is less sensitive to torque fluctuations due to non-zero friction in slide.

C) Idler without spring have some minor disadvantages: accurate and not-so-compact fixture and adjustment system and reverse bending of belt (not all belts are well suited for this).

D) Sliding motor withot spring is most rigid and precise system, but with drawback of no self-adjustment.

Thus I use idler+spring when I want to track torque by measurement of idler displacement (i.e. for emergency stop in a case of stuck) because this system is most responsive. And I use sliding motor without spring when I want precise and smooth rotation.

Sliding motor can be fixed in several vays. If one tighten it with screw in direction of belt stretching, he can adjust resulting tension by putting thin plates under motor. If tightening direction is perpendicular to stretching, one adjust tension by simple pulling and fix it with screw (with extra force to avoid slipping). Good idea is to use angular slide with one (adjustable) screw for stratching an other[s] for fixture in adjusted position.

There are different increments of timing belts, but not all of then are easy to order in retail quantities. One can think about 3d-printed or even lasercut custom belts for low-loaded drives. Reinforced DIY belts of free pitch and type can be mold with 3d-printed of lasercut circular gear-like trench template, filled by steel or glassfiber cord.

Pullyes can be very close, even intersect (with a slot or array of slots). Bu if they are too close, gears can be more useful.


The vendor McMaster has MXL timing belts at the following page: https://www.mcmaster.com/#timing-belts/=1bswega

Timings belts should have no or minimal slop. An easy way to remove slop is mount the motor using slots, position motor so belt is snug, and tighten screws holding motor in place.

I would try for 120 degree teeth engagement or more, but for a low load I don't thing the pulleys being close together will be an issue.


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