Gearbox and Transmission

This work-in-progress gearbox and transmission is for a model of a Churchill tank.


Hello Luka, I would like to help you with your impressive transmission project. We met at the SELMEC meeting but I did not ask for your contact details.

Thank you for getting in touch. It was great to meet you and the other SELMEC members and I have decided to join.

There are a couple of things in my model that I would like to ask your advice on and I shall follow up with an email.

I look forward to showing the club what I have come up with in the next meeting.

Hi Luka,

I am glad that you are making progress with your model. As I was unable to help at the meeting, I researched the Merritt-Brown transmission at home having studied and modelled Cletrac and double differential gearboxes previously. I have to admit that your model re-kindled my interest in the subject and decided that the best way to investigate it’s principles of operation was to model it myself. After quite a lot of work a model materialised. If you are interested, I could send you some images and description on receipt of your email address.

Hi again Luka,

I took some photos of your model and have studied them. My observations are: (1) The diff. , half shafts are geared to the steering epicyclic annuli (Ring gears)? They should be geared to the Brake drum/Sun gears of the steering epicyclics.

(2) The steering epicyclic planet carriers should be connected to the track drive sprockets. (3) Both steering epicyclic annuli (Ring Gears) should be connected together, carrying the gearbox output gear 57t (27a). (4) The planet pinions must be journaled to run freely on rigid pivot pins lock nutted to the planet carrier bush wheels. This is because all the gears must run free without any tendency to tilt, otherwise the drive will jamb. (5) The annuli must be concentric with their axis of rotation, otherwise the sun and planet pinions will bind. (6) Mounting the ring gears on couplings (63) makes it exceedingly difficult to maintain proper alignment and concentricity. This is because the tapped and clearance holes in couplings (63) are notoriously out of alignment. (7) Better to mount the ring gears onto face plates (109), loose on four lock nutted bolts.

Hope this helps.

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