I’ve been thinking about the Burrell gearing for some time. Calculating the overall ratio, estimating the maximum torque and speed of the traction engine.
Looking online a Mamod TE1a traction engine flywheel speed is between 2000rpm and 2500rpm.
1st stage engine to layshaft is 4:1 reduction
2nd stage layshaft to rear wheels is 4:1 reduction
This spring belt drive system gives an overall speed reduction of: 16:1
The rear wheels are 75mm in diameter.
Approximately 1.1 to 1.4mph.
The Live Steam Models 4″ scale SCC Burrell has two gear ratios of 7.6:1 and 6.3:1 overall.
1861 Locomotive Act, which regulated the use of steam locomotives and traction engines on the open road. It set a maximum speed of 10mph in open country and 5mph in towns, with fines of £10 for speeding (a term that has to be used loosely when the limit is 5mph).
Not so fast – roads.org.uk
1/20th Scale Burrell
Based on this my plan is to run with an overall ratio of 10:1. This feels like a sensible compromise. At 1000rpm on the engine this will give me a top speed of 1.1mph (Note: these calculations have been done with the excel Workshop Calculator – free to download).
This is equal to 0.5m/s and when you think in those terms that feels quite reasonable if you are running this engine on a table top.
Tractive Effort Check
12mm bore at 60psi is ~45N on the conrod
14mm stroke means ~0.32Nm of torque at the flywheel
hence 3.2Nm at the wheel (with a 10:1 gear ratio)
the drive wheels are 97mm OD and so hence 32N of tractive effort and the engine will be around 1.8 to 2kg
Also, I’m likely to run at a pressure of 45psi mostly and so I think around ~24N
That should be fine