Gears

Yeah, this is a rarely used type of high ratio reducer. There has been a challenge last yeah, where few people presented similar gearbox designs (but for a much lower power). I have been one of them. It has been fun to animate the motion of the parts!

Grabcad model

Grundfos Challenge - Dual Cycloidal Gearbox

This model represents my solution for the Grundfos Challenge. All necessary information can be found in the folder "documents" - Technical presentation - BOM - Section drawing - STEP model Searching for a compact high ratio gearbox I came up with the idea to use 2 cycloidal gearstages. In my opin...

This is hardly a new type of gearbox. I’ve been using them on machinery for over 40 years and have no doubt they've been around much longer than that.

They are not rare. You can achieve high gear ratios in a small space with this design. They have much higher efficiency than worm gear sets and can transmit much higher torque in a smaller space. The reason is the torque is transmitted using most all the teeth simultaneously rather than just a few and it’s a rolling rather than sliding contact. Lubrication is often just grease so mounting position does not matter and no vent is required. The design naturally has very very little backlash and that’s why they’re so popular in robotics but they great anywhere torque reverses. The only downside is typically they are only available in odd gear ratios. 5:1, 7:1, 11:1, 15:1 etc. Bearings are not spaced very far apart on the output shaft so you must also avoid excessive overhung loads.

in the Grundfos challenge, none of the entrys that used a worm gear reduction would have achieved the Design parameters of the challenge because of the low efficiency of a a worm drive. I did the calculations! On the other hand a cycloidal drive was an excellent method of achieving the high ratio and high efficiency. I did several designs using several methods but had other projects and just couldn’t meet the deadline.

Is is well known from 1920's. It is time to reveal new type. Does anybody hear about PRECESSION GEAR REDUCER?

It could has up to 1.000.000 gear ratio in a single stage, using common bevel gears.

It seems that you have some experience with robotic gearboxes?

What a pity you could not participate at the Grundfos challenge, sure your model wuould be great!

What I menat by saying "rare" is that you do not learn anything about cycloidal gearboxes in the studies and there is also not a lot of information about them in the classic literature...

Therefore also the Grundfos jury called it a "novel type of gearbox". I'm not happy about those words because cycloidal gearboxes aren't novel at all! I also agree with you that worm gears won't achieve the parameters because of the efficiency! Actually this was the keyword in the challenge, since the gearbox' ratios should be very high to fulfil the requierements!

Cheers,

Alex

I don’t have a lot of experience with robotics but I understand how cycloidal reducers can be easy to incorporate due to their inherent low backlash and high torque capabilities. Most of my experience has been in conveyor applications. Some of which used brake and clutch systems with high actuation forces. The cyclodial reducers took a lot of abuse and just never gave any problems.

I had done a lot of the preliminary engineering calculations for the Grundfos challenge. I looked at standard gearing, worm gears, and cycloidal gearing. Worm gearing just couldn’t meet the design parameters due to even the best efficiencies possible. Standard gearing had the most promise but was going to be very difficult to fit within the size constraints. Cycloidal gearing appeared to be the best choice. Unfortunately there’s very little engineering data available for actually designing cycloidal reducers. I couldn’t find any off-the-shelf cycloidal reducers that would fit the requirements of the challenge and I wasn’t comfortable trying to engineer something from scratch. I had too many other irons in the fire at the time to spend too much time on something that I probably lacked the skills to successfully complete. Although looking at the results of the competition I might not have done too bad!

I was disappointed that many of the challenge entries obviously didn’t take worm drive efficiency into consideration. When your dealing with high gear ratios, inefficiency can rob a very large percentage of the calculated torque. There were some beautiful designs that were destined to fail because they just hadn’t done their homework.

In the end I developed an appreciation for why Grundfos started the challenge to begin with. The challenge probably wasn’t impossible but was going to require a unique solution that pushed the envelope a little bit.