[yoyodyne]

Well,

I tested the motors under load and I got more or less the same result. To load them I put the robot on a ramp that I covered with my wife's sticky yoga mat so the wheels would not break free and raised the angle until at a motor PWM setting of 255 the robot managed to move a couple of inches in 1 second. I then measured the how far the robot went (actually the shaft encoder ticks) down to a PWM value of 220 for 6 trials and the average performance (sum of encoder ticks) for each PWM value was basically equal so the motors do seem to top out in both speed and torque around a positive PWM setting of 215. So I am applying the following linearization lookup:

DESIRED -> OUTPUT
255 232
254 232
253 223
252 217
251 215
250 214
249 214
248 213
247 213
246 212
245 212
244 211
243 211
242 210
241 208
240 206
239 204
238 203
237 202
236 200
235 199
234 197
233 196
232 195
231 194
230 193
229 192
228 191
227 189
226 188
225 186
224 185
223 184
222 183
221 182
220 181
219 180
218 179
217 178
216 177
215 177
214 176
213 176
212 175
211 174
210 173
209 172
208 172
207 171
206 171
205 170
204 170
203 169
202 168
201 168
200 168
199 167
198 167
197 166
196 166
195 165
194 165
193 164
192 164
191 163
190 163
189 163
188 162
187 162
186 161
185 161
184 160
183 160
182 160
181 159
180 159
179 158
178 158
177 158
176 157
175 157
174 157
173 156
172 156
171 156
170 156
169 155
168 155
167 154
166 154
165 154
164 154
163 153
162 153
161 153
160 153
159 152
158 152
157 152
156 152
155 151
154 151
153 151
152 150
151 150
150 149
149 149
148 149
147 149
146 148
145 148
144 148
143 148
142 148
141 148
140 147
139 147
138 147
137 147
136 147
135 146
134 146
133 146
132 146
131 146
130 145
129 145
128 145
127 127

With this applied the resulting motor speed is as shown in R LIN, L LIN lines on the attached graph.